bronco944
Pro Bodybuilder
found this full text article last night for a school paper. looks interesting to me at least.
Contraceptive efficacy of testosterone-induced azoospermia in normal men.
Abstract: The goal of developing a safe, effective, reversible method of male contraception has been elusive. Only two methods of contraception are generally used by men: vasectomy, which is not reversible, and condoms, which are not fully effective. For two decades researchers have evaluated the ability of androgens (male hormones) to suppress sperm production, but they have not documented whether this results in effective contraception. The current study, conducted in 10 centers and 7 countries, assessed the efficacy of hormonally-induced azoospermia (lack of sperm) in 271 fertile men with regular partners. Once a week for 12 months each subject received an injection of 200 milligrams of testosterone enanthate, a long-acting form of testosterone, a naturally occurring male hormone. Testosterone enanthate proved to be efficacious in preventing conception; the results indicate that this method is comparable to injectable female contraceptives, more effective than birth control pills and intrauterine devices (IUDs), and substantially better than condoms in preventing pregnancy. One pregnancy occurred, but was described as ''possibly extramarital'', a potentially confounding factor in any study of male contraception. Although the male hormones are considered to be safe, the possibility of long-term side effects, such as cardiovascular and prostatic diseases, is unknown. Large-scale surveillance is needed to assess these risks. None of the men dropped out of the study because of serious side effects. Sixty-eight men were eliminated because azoospermia was not achieved within six months. The most common reasons cited by those who discontinued their participation were: difficulty complying with the weekly injection schedule, acne, separation or divorce from partner, and moving from the area. At the end of the study period, 230 men recovered normal sperm production within a median of 3.7 months. Although testosterone-induced azoospermia is an effective method of contraception, it may not be practical, at least with weekly injections. A second stage of this study will determine whether suppressing sperm production to a particular level results in effective contraception. (Consumer Summary produced by Reliance Medical Information, Inc.)
Full Text: COPYRIGHT 1990 The Lancet Ltd.
Contraceptive efficacy of testosterone-induced azoospermia in normal men A multicentre study (ten centres) in seven countries was done to assess the contraceptive efficacy of hormonally-induced azoospermia in 271 healthy fertile men. Each subject received 200 mg testosterone enanthate weekly by intramuscular injection. 157 men (cumulative rate at 6 months 65%) became azoospermic in three consecutive semen samples. These men entered a 12-month efficacy phase during which continuing testosterone injections were the only form of contraception. There was 1 pregnancy during 1486 months of the efficacy phase (0.8 conceptions [95% confidence interval 0.02-4.5] per 100 person-years). Discontinuations from the study were mainly because azoospermia was not achieved within 6 months and because of dislike of the injection schedule. The mean time to become azoospermic was 120 days (SD 40)> reappearance of spermatozoa was detected in 11 men and in no case led to discontinuation from the study or to pregnancy. After the testosterone injections had been stopped, the estimated median time from azoospermia to recovery (sperm concentration of at least 20 million/ml) was 3.7 months (3.6-3.9) and to the subject's mean baseline sperm concentration was 6.7 months (6.2-8.7). Hormonal regimens that induce azoospermia can provide highly effective, sustained, and reversible male contraception with minimum side-effects.
Introduction
The development of safe, effective, and reversible contraceptive methods for men is an important goal in expanding the choices available for couples to regulate family size. The shortcomings of the currently available methods are a major barrier to the greater involvement of men in family planning. Nonetheless, that nearly 60 million men have had a vasectomy [1] and nearly 40 million use condoms, [2] indicates that men already have a wide involvement in family planning.
A hormonal contraceptive method for men must reduce the production of viable spermatozoa consistently to cause temporary infertility. Studies over the past two decades have assessed whether androgens alone [3-5] or combined with progestagens [6] can induce azoospermia in healthy fertile men. Since the endpoint of these studies was sperm output and the couples used additional contraception, quantitative estimates of contraceptive efficacy attributable to suppression of spermatogenesis could not be derived. [7]
The present multicentre study was done to clarify whether induced azoospermia is sufficient for male contraception. For ethical reasons this question was split into two stages. The first stage was to see whether hormonally-induced azoospermia could be sustained and provide effective male contraception for up to 12 months. If the first stage was successful, the second stage would be to determine whether suppression to a defined level of oligozoospermia was also adequate. This report presents the results from the first stage of the first formal efficacy study of a hormonal male contraceptive.
Subjects and methods
The fertility of normal men made azoospermic by weekly injections of testosterone enanthate was studied over 12 months during which testosterone injections were the only form of contraception. Thus, the study tested the hypotheses that hormonally-induced azoospermia in healthy fertile men could be maintained consistently for up to 12 months after induction and also provide safe, effective, and reversible contraception. Despite the obvious impracticality of weekly injections of testosterone enanthate for wide-scale use, the hormonal regimen was selected because its safety, reversibility, and efficacy in making healthy fertile men azoospermic is well known. [3-5,8] The practicality of testosterone enanthate as a contraceptive method was not investigated.
Subjects
Healthy men between 21 and 45 years of age were eligible if they were in a stable relationship in which both partners wanted contraception> if they had no active or chronic medical (cardiac, hepatic, renal, or prostatic) disease> if their partners were not older than 35 years, had regular menses, and no history of pelvic inflammatory disease> and if the couple had no history of infertility (defined as failing to conceive after regular unprotected intercourse for more than a year). Volunteers also had routine medical examinations, including rectal palpation of the prostate and estimation of testicular size by orchiometer, except in the Seattle centre where calipers were used. The men provided two sets of semen and blood samples for assays of reproductive hormones (luteinising hormone [LH], follicle stimulating hormone [FSH], testosterone), full blood count (haemoglobin, leucocytes, platelets), liver function (serum aspartate aminotransferase, serum alanine aminotransferase, guanosine triphosphate), and cholesterol fractions (high-density lipoprotein and low-density lipoprotein). To be eligible for the study, both semen analyses had to have sperm concentrations exceeding 20 million/ml with greater than 50% normal forms and greater than 50% forward motility, and all biochemical variables had to be within the normal limits for that centre.
Study design
The protocol, which was designed by the Steering Committee of the World Health Organisation (WHO) Task Force on Methods for the Regulation of Male Fertility, was approved by the WHO Toxicology Group, Scientific and Ethical Review Group, and Secretariat Committee on Research Involving Human Subjects. The study was also approved by each local institutional human ethical review committee and national regulatory authority where required. The men and their partners had to provide witnessed written informed consent.
The study consisted of suppression, efficacy, and recovery phases. Eligible mean entered the suppression phase starting from the date of the first injection of testosterone enanthate (200 mg, intramuscular as 0.8 ml of 'Testoviron-Depot 250', Schering AG, Berlin or as 1.0 ml of 'Delatestryl', ER Squibb, Princeton, NJ for the US centre). Weekly testosterone injections were given by study personnel, except under exceptional circumstances (eg, travel, illness) when the administration of injections elsewhere was arranged. Subjects more than 2 days late for any injection were excluded from the study for protocol violation. Testosterone injections continued either until the man became azoospermic (defined as 3 consecutive azoospermic specimens at 2-week intervals) or until 6 months elapsed without azoospermia having been achieved (non-suppression). By 2 months into the suppression phase, all couples in which the female partner was using a hormonal contraceptive method were required to switch to a barrier method.
As soon as the man became azoospermic, the couple entered the 12-month efficacy phase starting from the date of the third azoospermic specimen. All other contraception was stopped and weekly testosterone injections were continued. Couples were free to withdraw from the study at any stage.
After the testosterone injections had stopped, men entered the recovery phase, which started from the date of the last injection. Men were to be followed at monthly intervals until spermatogenesis recovered--ie, a sperm concentration of 20 million/ml or their own baseline level. During the suppression and recovery phases the couples were advised to continue the use of other contraceptive methods, with the exception of planned pregnancies during recovery.
Monitoring
During the suppression phase, semen was collected at monthly intervals for the first 2 months and then every 2 weeks for the remainder of the suppression phase. During the efficacy phase, semen analyses were done every month> if any semen sample contained more than 1 million sperm in an ejaculate of at least 1.0 ml in volume, that man provided a repeat semen sample 2 weeks later. Men were excluded if there was a similar amount of spermatogenic rebound in the second sample. During the suppression and efficacy phases, couples kept a diary of menstrual bleeding and sexual activity. From the start of testosterone injections, men were examined by a physician every 3 months> the examination included rectal palpation of the prostate, and blood samples were taken for the measurement of routine biochemical and haematological indices and reproductive hormones as at the entry examination. Testosterone injections were to be stopped in the event of adverse drug reaction> serious intercurrent medical illness> persistent abnormalities of liver function or cholesterol> rise in blood pressure or packed cell volume> or if injections were not given within 2 days of schedule.
Laboratory methods
Semen samples were provided by masturbation and were analysed according to WHO methods. [9] LH, FSH, and testosterone were measured by radioimmunoassay at each center with WHO reagents and methods [10] or other standards [11-14] (two centres). Routine haematological and biochemical assays were done by the standard methods of each centre.
Data analysis
All information was recorded on specially designed forms which were collated at the data coordinating centre in Geneva. Two-way analysis of variance was used to adjust for between-centre differences when groups of subjects were compared. Sperm concentration was analysed after logarithmic transformation to reduce its skewness. Because of between-centre differences in routine laboratory methods, serial results were expressed as a percentage change from the subject's own baseline pretreatment levels. Discontinuations of injections were grouped according to the reason why they were stopped> rates were calculated with the use of lifetable methods [15] or as Pearl rates expressed as events per 100 person-years, with confidence intervals calculated from the Poisson distribution. [16] The exposure time for each subject was taken as the interval between the first and last injections. Body surface area (BSA, [m.sup.2] was calculated with the duBois formula [17] and body mass index (BMI, kg/[m.sup.2] as weight (kg) divided by the square of height (m). Data are expressed as mean and standard deviation unless otherwise indicated.
Results
Subjects
The men were broadly similar at entry (table I), apart from those in the Chinese centres who were smaller. The mean age of the partners of the men who entered the study was 29.2 years (4.1). Fertility had been established in that relationship in 228 (84%) of 271 couples--a median of 2 completed pregnancies and the most recent conception at a median of 24 months before entry to the study. Before entry couples were using female hormonal contraception (59, 22%), intrauterine devices (62, 23%), or barrier (117, 43%) or other (33, 12%) methods of contraception.
Suppression phase
A total of 157 men (58%) became azoospermic and 119 completed the efficacy phase as planned. 114 (42%) withdrew from the study during the suppression phase and 38 (14%) during the efficacy phase (table II). More than half the men who stopped having injections in the suppression phase (68/114) were for non-suppression, with a cumulative lifetable rate of 23%, within 6 months of the start of injections. The mean minimum sperm concentration among the non-suppressors was 3.0 million/ml (5.8). The 6-month cumulative lifetable rate of becoming azoospermic was 64.5% (SE 3.5%)> 70% of men who completed the suppression phase became azoospermic (table I). This rate varied significantly between centres (p=0.001)> the three Chinese centres had a higher rate (mean 91%) than the others (mean 60%). Among men who became azoospermic, the mean time from the first injection to the third consecutive azoospermic sample was 120 days (40.1). There were no significant differences between suppressors and non-suppressors (after adjustment for between-centre differences) in all the baseline indices--ie, age, height, weight, BSA, BMI, mean testis volume, or pretreatment sperm concentration or motility (table III).
After starting testosterone injections there were increases in body weight (3.7%), SE 0.3%), haemoglobin (5.7%, SE 0.5%), and testosterone (142%, SE 10%), and decreases in testicular volume (16.5%, SE 2.1%), plasma urea (8.4%, SE 1.6%), LH (66.7%, SE 2.1%), and FSH (62.5%, SE 2.1%)> these changes were similar in men who became azoospermic to those who did not. The values returned to baseline in the recovery period.
8 men stopped having injections because their partner became pregnant during the suppression phase (table II), despite the agreement to use other forms of contraception at this time. The overall compliance rate with this instruction is unknown. Additionally, a pregnancy in the partner of a man who had stopped having injections because of non-suppression was confirmed two weeks after the last injection> the estimated gestational age was 12 weeks. The outcome of these pregnancies was 5 terminations, 3 healthy live births, and 1 unknown.
Contraceptive efficacy
There was 1 pregnacy during the 1486 months of the efficacy phase (Pearl rate 0.8 [95% confidence interval 0.02-4.5] per 100 person-years). All semen samples in this subject, including those before and after the estimated date of conception, were asoospermic. The pregnancy was terminated. In the efficacy phase (ie, among men who were already azoospermic in at least 3 consecutive specimens), sperm were seen in 21 (1.4% of 1515 samples. These samples were from 11 men--median of 1 non-azoospermic sample per subject (range 1-8)> in no case were injections stopped for spermatogenic rebound, nor did any of the partners of these men become pregnant.
Discontinuations
2 men were discontinued from the study during the efficay phase for protocol violation since they were found on review not to satisfy the admission criteria (female partner aged 36 years, and pre-existing cor pulmonale). A total of 15 men discontinued during the suppression and efficacy phases because of difficulties associated with the injection (annual rate 7.5%)--ie, dislike of the frequency of injections (5), pain (6) or infection (1), at the injection site, or injections not given within the prescribed time interval (3). 52 men also stopped having injections for medical or personal reasons, with annual cumulative rates of 11.9% and 12.7%, respectively. The medical reason (27 men) were acne (9), increased aggressiveness and libido (3), weight gain (2), raised packed cell volume and haemoglobin (2), abnormal lipids (2), hypertension (1), depression (1), tiredness (1), aphthosis (1), acute prostatis (1), pneumonia (1), and Gilbert's syndrome (1)> 2 partners had dysmenorrhoea (1) and unspecified neurological illness (1). There were no discontinuations due to prostatic enlargement, abnormality of liver enzymes, or complaints of reduction in testicular size. Personal reasons (25 men) were unwillingness to continue with the study (10), separation or divorce from partner (9), moving away from the study site (4), or a planned pregnancy (2). 6 men were lost to follow-up, only 1 of whom had entered the efficacy phase.
Recovery
To date, recovery information is available for 230 men (85%)> the sperm concentration of 192 (84%) of these men has returned to 20 million/ml and 106 (46%) to their own baseline level. The median time to recovery to 20 million/ml was 3.7 months (95% CI, 3.6-3.9) in the men who had become azoospermic, 3.0 months (2.8-3.4) in non-suppressors, and 3.9 months (2.9-9.5) among men who discontinued testosterone infections for other reasons. Equivalent data for return to subject's own geometric mean baseline sperm concentration are 6.7 (6.2-8.7), 5.7 (4.0-12.9), and 9.0 (4.6-13.9) months, respectively.
Although only a few couples planned pregnancies after completion of this study, 11 conceptions have been recorded in the recovery phase to date (1 of which was known to be by a man other than the partner). There have been 2 terminations of pregnancy, 1 spontaneous abortion, and 4 normal live births. Partners of the 2 men who stopped receiving injections because the couple planned another pregnancy both became pregnant in the recovery phase.
Discussion
This study has shown that in healthy fertile men rendered azoospermic (as assessed by semen analysis with conventional methods) by weekly injections of testosterone enanthate, this regimen can maintain safe, stable, effective, and reversible contraception for at least 12 months. The contraceptive efficacy in this study was high> it is comparable with typical first-year failure rates of female injectable contraceptives (0.2-0.4 per 100 persons-years)> is better than that of female oral contraceptives (3 per 100 person-years) and IUDs, (6 per 100 person-years)> and is substantially better than of condoms (12 per 100 person-years)--the only available reversible male contraceptive. [18] If the 1 efficacy phase pregnancy (which was possibly "extramarial") was exluded from analysis, the upper 95% CI of the pregnancy rate would be lowered from 4.5 to 3.0 per 100 person-years. Such contraceptive failures are possible in a study of male contraception since the untreated partner becomes pregnant. By contrast, in studies of female contraception, any pregnancy can be directly identified as a contraceptive failure. Pregnancies in the suppression phase can be expected when fertile couples are instructed to change to barrier contraceptive methods. Other methods of inducing azoospermia by the suppression of gonadotropin secretion (eg, gonadotropin-releasing hormone antagonists [19]) might lead to similar patterns of contraceptive efficacy).
The overall safety of testosterone enanthate administration has already been well established during decades of widespread clinical use. [3-5,8] The low rates of discontinuation due to side-effects of the hormone and incidental medical conditions in this study confirms the safety and acceptability of such androgen administration found in studies with up to 18 months exposure. Moreover, the cumulative discontinuation rates for medical events was low and the compliance high in view of the prolonged and demanding nature of the study. The long-term theoretical hazards from the use of androgens might include risks of prostatic and cardiovascular disease. The real hazards remain uncertain and, although the present findings are reassuring in the short term, better quantitative monitoring methods are needed for large-scale surveillance, which would be required to quantify or exclude small risks. The possible long-term benefits from androgen use for bone, muscle, and blood metabolism will also need to be assessed before the nest risk-benefit effects of an androgen-containing regimen can be fully evaluated.
The two major limitations of this regimen are the frequency of injections and the inability uniformly to induce azoospermia. The injection schedule was a major cause for discontinuation, although there was a high rate of compliance by subjects remaining in the study. The maintenance of azoospermia and good contraceptive efficacy was not compromised by a tolerance of 2 days in timing of the weekly injections. The advent of long acting depot testosterone prepations, such as the new WHO-National Institutes of Child Health and Human Development ester 20-AET-1, [20,21] or other testosterone preparations [22,23] which allow androgen administration at intervals of at least 3-4 months would provide a more acceptable method of androgen replacement.
The pronounced heterogeneity in rates of azoospermia between centres is not explained by differences in body size of the men. The lack of a relation between body weight and the likelihood of becoming azoospermic is supported by studies which show that even 50% [24] or greater [8] increases in dose of testosterone enanthate do not cause azoospermia uniformly in Caucasian men. Thus, the use of a fixed androgen dose in centres where there were differences of up to 30% in body weight (20% in BSA) does not explain the different suppression rates. The similar effects of testosterone on body weight gain> rise in haemoglobin> and decrease in plasma urea, LH, and FSH in the suppressors and non-suppressors may indicate that azoospermia is a specific effect of testosterone on spermatogenesis and is not due to variations in testosterone levels, sensitivity to testosterone, or to suppression of gonadotropins. Differences in suppression rates are unlikely to be due to differential rates of compliance with treatment.
This study shows that the laboratory diagnosis of azoospermia corresponds with highly effective contraception, which is rarely followed by resumption of spermatogenesis when regular compliance with hormonal injections is guaranteed. The negligible risk of prenancy in this study implies either than fertile spermatozoa are absent or that those still present in the ejaculate are so few or have such depleted fertilising capacity that conception after intercourse is unlikely. Recent studies have suggested that residual sperm during incomplete suppression of spermatogenesis have decreased fertilising capacity as judged by their ability to penetrate zona-free hamster oocytes. [25,26] Thus, azoospermia many not be necessary for adequate inhibition of male fertility to provide effective contraception and this question is being addressed in the second stage of the study.
* Principal investigators and centres: Dr Zhang Gui-yuan, National Research Institute for Family Planning, Beijing China> Dr Li Guo-zhu, Family Planning Research Institute of Sichuan, chengdu, China> Dr F. C. W. Wu, Centre for Reproductive Biology, Edinburgh, UK> Dr H. W. G. Baker, Prince Henry's Institute of Medical Research, Melbourne, Australia> Dr Wang Xing-hai, Jiangsu Family Planning Institute, Nanjing, china> Dr J. C. Soufir, Universite Paris-Sud, Paris, France> Dr I Huhtaniemi, University of Turku, Turku, Finland> Dr C. A. Paulsen, University of Washington, Seattle, USA> Dr C. Gottlieb, Karolinska Hospital, Stockholm, Sweden> Dr D. J. Handelsman, University of Sydney, Sydney, Australia.
Study and data coordination: Dr T. M. M. Farley, Ms C. Hazelden, Mr A. Peregoudov, Dr G. M. H. Waites, Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organisation, Geneva, Switzerland.
Manuscript prepared by: Dr D. J. Handelsman, University of Sydney Sydney, Australia> Dr T. M. M. Farley, Dr G. M. H. Waites, Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organisation, GEneva, Switzerland.
Correspondence to Dr G. M. H. Waites, Special Programme of Research, Development and Research Training in Human Reproduction, World Health ORganisation, 1211 Geneva 27, Switzerland.
REFERENCES
[1.] Ross JA, Hong S, Huber DH. Voluntary sterilization: an international fact book. New York: Association for Voluntary Surgical Contraception, 1985.
[2.] Maudlin WP, Segal SJ. Prevalence of contraceptive use: trends and issues. Stud Fam Plan 1988> 19: 335-53.
[3.] Rowley MJ, Heller CG. Summary of studies utilizing androgens in the normal human male. Patanelli DJ, ed. Hormonal control of male fertility. US Department of Health, Education and Welfare, Publication No (NIH) 78-1097, 1978: 145-66.
[4.] Paulsen CA, Leonard JM, Burgess EC, Ospina LF. Male contraceptive development: re-examination of testosterone enanthate as an effective single agent. In: Patanelli DJ, ed. Hormonal control of male fertility. US Department of Health, Education and Welfare, Publication No (NIH) 78-1097, 1978: 17-36.
[5.] Swerdloff RS, Palacios A, McClure RD, Campfield RD, Brosman SA. Clinical evaluation of testosterone enanthate in the reversible suppression of spermatogenesis in the human male: efficacy, mechanism of action and adverse effects. In: Patanelli DJ, ed. Hormonal control of male fertility. US Department of Health, Education and Welfare, Publication No (NIH) 78-1097, 1978: 41-63.
[6.] Schearer SB, Alvarez-Sanchez F, Anselmo J, et al. Hormonal contraception for men. Int F Androl 1978> (suppl 2)> 680-712.
[7.] Barfield A, Melo J, Coutinho E, et al. Pregnancies associated with sperm concentrations below 10 million/ml in clinical studies of a potential male contraceptive method, depot medroxy progesterone acetate and testosterone esters. Contraception 1979> 20: 121-27.
[8.] Patanelli DJ. Hormonal control of male fertility. US Department of Health, Education and Welfare, Publication No (NIH) 78-1097, 1978.
[9.] World Health Organisation. Laboratory manual for the examination of human semen and semen-cervical mucus interaction. 2nd ed. Cambridge: Cambridge University Press, 1987.
[10.] Sufi SB, Donaldson A, Jeffcoate SL, eds. Programme for the provision of matched assay reagents for the radioimmunoassay of hormones in reproductive physiology. Method manual. 10th ed. Geneva: World Health Organization, 1986.
[11.] Hunter WM, Bernie JG. Reduction of non-specific serum responses in human pituitary gonadotrophin radioimmunoassays. F Endocrinol 1979> 80: 59O8.
[12.] Bremner WJ, Matsumoto AM, Sussman AM, Paulsen CA. Follicle stimulating hormone and human spermatogenesis. F Clin Invest 1981> 68: 1044-52.
[13.] Corker CS, Davidson DW. A radioimmunoassay for testosterone in various biological fluids without chromatography. F Steroid Biochem 1978> 9: 373-74.
[14.] Matsumoto AM, Paulsen CA, Hopoper BR, Rebar RW, Bremner WJ. Human chorionic gonadotrophin and testicular function: stimulation of testosterone, testosterone, precursors and sperm production despite high estradiol levels. F Clin Endocrinol Metab 1983> 56: 720-28.
[15.] Farley TMMM. Life -table methods for contraceptive research. Stat Medicine 1986> 5: 475-89.
[16.] Gardner MJ, Altman DG, eds. Statistics with confidence: confidence intervals and statistical guidelines. London: British Medical Journal, 1989.
[17.] du Bois, D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med 1916> 17: 863-71.
[18.] Trussell J, Kost K. Contraceptive failure in the United States: a critical review of the literature. Stud Fam Plan 1987> 18: 237-83.
[19.] Weinbauer GF, Khurshid S, Fingscheidt U, Nieschlag E. Sustained inhibition of sperm production and inhibin secretion induced by a gonadotropin-releasing hormone antagonist and delayed testosterone substitution in non-human primates (Macaca fascicularis). F Endocrinol 1989> 123: 303-10.
[20.] Weinbauer GF, Marshall GR, Nieschlag E. New injectable testosterone ester maintains serum testosterone of castrated monkeys in the normal range for four months. Acta Endocrinologica 1986> 113: 128-32.
[21.] Rajalakshmi M, Ramakrishnan PR. Pharmacokinetics and pharmacodynamics of a new long-acting androgen ester: maintenance of physiological levels for 4 months after a single injection. Contraception 1989> 40: 399-412.
[22.] Burris AS, Ewing LL, Sherins RJ. Initial trial of slow-release testosterone microspheres in hypogonadal men. Fertil Steril 1988> 50: 493-97.
[23.] Handelsman DJ, Conway AJ, Boylan LM. Pharmacokinetics and pharmacodynamics of testoterone pellets in man. F Clin Endocrinol Metab 1990> 71: 216-22.
[24.] Matsumoto AM. Effects of chronic testosterone administration in normal men: safety and efficay of high dosage testosterone and parallel dose-dependnt suppression of luteinizing hormone, follicle-stimulating-hormone, and sperm production. F Clin Endocrinol Metab 1990> 70: 282-87.
[25.] Matsumoto AM. Is high dosage testosterone an effective male contraceptive agent? Fertil Steril 1988> 50: 324-28.
[26.] Wu FCW, Aitken RJ. Suppression of sperm function by medroxyprogesterone acetate and testosterone enanthate in steroid male contraception. Fertil Steril 1989> 51: 691-98.
Contraceptive efficacy of testosterone-induced azoospermia in normal men.
Abstract: The goal of developing a safe, effective, reversible method of male contraception has been elusive. Only two methods of contraception are generally used by men: vasectomy, which is not reversible, and condoms, which are not fully effective. For two decades researchers have evaluated the ability of androgens (male hormones) to suppress sperm production, but they have not documented whether this results in effective contraception. The current study, conducted in 10 centers and 7 countries, assessed the efficacy of hormonally-induced azoospermia (lack of sperm) in 271 fertile men with regular partners. Once a week for 12 months each subject received an injection of 200 milligrams of testosterone enanthate, a long-acting form of testosterone, a naturally occurring male hormone. Testosterone enanthate proved to be efficacious in preventing conception; the results indicate that this method is comparable to injectable female contraceptives, more effective than birth control pills and intrauterine devices (IUDs), and substantially better than condoms in preventing pregnancy. One pregnancy occurred, but was described as ''possibly extramarital'', a potentially confounding factor in any study of male contraception. Although the male hormones are considered to be safe, the possibility of long-term side effects, such as cardiovascular and prostatic diseases, is unknown. Large-scale surveillance is needed to assess these risks. None of the men dropped out of the study because of serious side effects. Sixty-eight men were eliminated because azoospermia was not achieved within six months. The most common reasons cited by those who discontinued their participation were: difficulty complying with the weekly injection schedule, acne, separation or divorce from partner, and moving from the area. At the end of the study period, 230 men recovered normal sperm production within a median of 3.7 months. Although testosterone-induced azoospermia is an effective method of contraception, it may not be practical, at least with weekly injections. A second stage of this study will determine whether suppressing sperm production to a particular level results in effective contraception. (Consumer Summary produced by Reliance Medical Information, Inc.)
Full Text: COPYRIGHT 1990 The Lancet Ltd.
Contraceptive efficacy of testosterone-induced azoospermia in normal men A multicentre study (ten centres) in seven countries was done to assess the contraceptive efficacy of hormonally-induced azoospermia in 271 healthy fertile men. Each subject received 200 mg testosterone enanthate weekly by intramuscular injection. 157 men (cumulative rate at 6 months 65%) became azoospermic in three consecutive semen samples. These men entered a 12-month efficacy phase during which continuing testosterone injections were the only form of contraception. There was 1 pregnancy during 1486 months of the efficacy phase (0.8 conceptions [95% confidence interval 0.02-4.5] per 100 person-years). Discontinuations from the study were mainly because azoospermia was not achieved within 6 months and because of dislike of the injection schedule. The mean time to become azoospermic was 120 days (SD 40)> reappearance of spermatozoa was detected in 11 men and in no case led to discontinuation from the study or to pregnancy. After the testosterone injections had been stopped, the estimated median time from azoospermia to recovery (sperm concentration of at least 20 million/ml) was 3.7 months (3.6-3.9) and to the subject's mean baseline sperm concentration was 6.7 months (6.2-8.7). Hormonal regimens that induce azoospermia can provide highly effective, sustained, and reversible male contraception with minimum side-effects.
Introduction
The development of safe, effective, and reversible contraceptive methods for men is an important goal in expanding the choices available for couples to regulate family size. The shortcomings of the currently available methods are a major barrier to the greater involvement of men in family planning. Nonetheless, that nearly 60 million men have had a vasectomy [1] and nearly 40 million use condoms, [2] indicates that men already have a wide involvement in family planning.
A hormonal contraceptive method for men must reduce the production of viable spermatozoa consistently to cause temporary infertility. Studies over the past two decades have assessed whether androgens alone [3-5] or combined with progestagens [6] can induce azoospermia in healthy fertile men. Since the endpoint of these studies was sperm output and the couples used additional contraception, quantitative estimates of contraceptive efficacy attributable to suppression of spermatogenesis could not be derived. [7]
The present multicentre study was done to clarify whether induced azoospermia is sufficient for male contraception. For ethical reasons this question was split into two stages. The first stage was to see whether hormonally-induced azoospermia could be sustained and provide effective male contraception for up to 12 months. If the first stage was successful, the second stage would be to determine whether suppression to a defined level of oligozoospermia was also adequate. This report presents the results from the first stage of the first formal efficacy study of a hormonal male contraceptive.
Subjects and methods
The fertility of normal men made azoospermic by weekly injections of testosterone enanthate was studied over 12 months during which testosterone injections were the only form of contraception. Thus, the study tested the hypotheses that hormonally-induced azoospermia in healthy fertile men could be maintained consistently for up to 12 months after induction and also provide safe, effective, and reversible contraception. Despite the obvious impracticality of weekly injections of testosterone enanthate for wide-scale use, the hormonal regimen was selected because its safety, reversibility, and efficacy in making healthy fertile men azoospermic is well known. [3-5,8] The practicality of testosterone enanthate as a contraceptive method was not investigated.
Subjects
Healthy men between 21 and 45 years of age were eligible if they were in a stable relationship in which both partners wanted contraception> if they had no active or chronic medical (cardiac, hepatic, renal, or prostatic) disease> if their partners were not older than 35 years, had regular menses, and no history of pelvic inflammatory disease> and if the couple had no history of infertility (defined as failing to conceive after regular unprotected intercourse for more than a year). Volunteers also had routine medical examinations, including rectal palpation of the prostate and estimation of testicular size by orchiometer, except in the Seattle centre where calipers were used. The men provided two sets of semen and blood samples for assays of reproductive hormones (luteinising hormone [LH], follicle stimulating hormone [FSH], testosterone), full blood count (haemoglobin, leucocytes, platelets), liver function (serum aspartate aminotransferase, serum alanine aminotransferase, guanosine triphosphate), and cholesterol fractions (high-density lipoprotein and low-density lipoprotein). To be eligible for the study, both semen analyses had to have sperm concentrations exceeding 20 million/ml with greater than 50% normal forms and greater than 50% forward motility, and all biochemical variables had to be within the normal limits for that centre.
Study design
The protocol, which was designed by the Steering Committee of the World Health Organisation (WHO) Task Force on Methods for the Regulation of Male Fertility, was approved by the WHO Toxicology Group, Scientific and Ethical Review Group, and Secretariat Committee on Research Involving Human Subjects. The study was also approved by each local institutional human ethical review committee and national regulatory authority where required. The men and their partners had to provide witnessed written informed consent.
The study consisted of suppression, efficacy, and recovery phases. Eligible mean entered the suppression phase starting from the date of the first injection of testosterone enanthate (200 mg, intramuscular as 0.8 ml of 'Testoviron-Depot 250', Schering AG, Berlin or as 1.0 ml of 'Delatestryl', ER Squibb, Princeton, NJ for the US centre). Weekly testosterone injections were given by study personnel, except under exceptional circumstances (eg, travel, illness) when the administration of injections elsewhere was arranged. Subjects more than 2 days late for any injection were excluded from the study for protocol violation. Testosterone injections continued either until the man became azoospermic (defined as 3 consecutive azoospermic specimens at 2-week intervals) or until 6 months elapsed without azoospermia having been achieved (non-suppression). By 2 months into the suppression phase, all couples in which the female partner was using a hormonal contraceptive method were required to switch to a barrier method.
As soon as the man became azoospermic, the couple entered the 12-month efficacy phase starting from the date of the third azoospermic specimen. All other contraception was stopped and weekly testosterone injections were continued. Couples were free to withdraw from the study at any stage.
After the testosterone injections had stopped, men entered the recovery phase, which started from the date of the last injection. Men were to be followed at monthly intervals until spermatogenesis recovered--ie, a sperm concentration of 20 million/ml or their own baseline level. During the suppression and recovery phases the couples were advised to continue the use of other contraceptive methods, with the exception of planned pregnancies during recovery.
Monitoring
During the suppression phase, semen was collected at monthly intervals for the first 2 months and then every 2 weeks for the remainder of the suppression phase. During the efficacy phase, semen analyses were done every month> if any semen sample contained more than 1 million sperm in an ejaculate of at least 1.0 ml in volume, that man provided a repeat semen sample 2 weeks later. Men were excluded if there was a similar amount of spermatogenic rebound in the second sample. During the suppression and efficacy phases, couples kept a diary of menstrual bleeding and sexual activity. From the start of testosterone injections, men were examined by a physician every 3 months> the examination included rectal palpation of the prostate, and blood samples were taken for the measurement of routine biochemical and haematological indices and reproductive hormones as at the entry examination. Testosterone injections were to be stopped in the event of adverse drug reaction> serious intercurrent medical illness> persistent abnormalities of liver function or cholesterol> rise in blood pressure or packed cell volume> or if injections were not given within 2 days of schedule.
Laboratory methods
Semen samples were provided by masturbation and were analysed according to WHO methods. [9] LH, FSH, and testosterone were measured by radioimmunoassay at each center with WHO reagents and methods [10] or other standards [11-14] (two centres). Routine haematological and biochemical assays were done by the standard methods of each centre.
Data analysis
All information was recorded on specially designed forms which were collated at the data coordinating centre in Geneva. Two-way analysis of variance was used to adjust for between-centre differences when groups of subjects were compared. Sperm concentration was analysed after logarithmic transformation to reduce its skewness. Because of between-centre differences in routine laboratory methods, serial results were expressed as a percentage change from the subject's own baseline pretreatment levels. Discontinuations of injections were grouped according to the reason why they were stopped> rates were calculated with the use of lifetable methods [15] or as Pearl rates expressed as events per 100 person-years, with confidence intervals calculated from the Poisson distribution. [16] The exposure time for each subject was taken as the interval between the first and last injections. Body surface area (BSA, [m.sup.2] was calculated with the duBois formula [17] and body mass index (BMI, kg/[m.sup.2] as weight (kg) divided by the square of height (m). Data are expressed as mean and standard deviation unless otherwise indicated.
Results
Subjects
The men were broadly similar at entry (table I), apart from those in the Chinese centres who were smaller. The mean age of the partners of the men who entered the study was 29.2 years (4.1). Fertility had been established in that relationship in 228 (84%) of 271 couples--a median of 2 completed pregnancies and the most recent conception at a median of 24 months before entry to the study. Before entry couples were using female hormonal contraception (59, 22%), intrauterine devices (62, 23%), or barrier (117, 43%) or other (33, 12%) methods of contraception.
Suppression phase
A total of 157 men (58%) became azoospermic and 119 completed the efficacy phase as planned. 114 (42%) withdrew from the study during the suppression phase and 38 (14%) during the efficacy phase (table II). More than half the men who stopped having injections in the suppression phase (68/114) were for non-suppression, with a cumulative lifetable rate of 23%, within 6 months of the start of injections. The mean minimum sperm concentration among the non-suppressors was 3.0 million/ml (5.8). The 6-month cumulative lifetable rate of becoming azoospermic was 64.5% (SE 3.5%)> 70% of men who completed the suppression phase became azoospermic (table I). This rate varied significantly between centres (p=0.001)> the three Chinese centres had a higher rate (mean 91%) than the others (mean 60%). Among men who became azoospermic, the mean time from the first injection to the third consecutive azoospermic sample was 120 days (40.1). There were no significant differences between suppressors and non-suppressors (after adjustment for between-centre differences) in all the baseline indices--ie, age, height, weight, BSA, BMI, mean testis volume, or pretreatment sperm concentration or motility (table III).
After starting testosterone injections there were increases in body weight (3.7%), SE 0.3%), haemoglobin (5.7%, SE 0.5%), and testosterone (142%, SE 10%), and decreases in testicular volume (16.5%, SE 2.1%), plasma urea (8.4%, SE 1.6%), LH (66.7%, SE 2.1%), and FSH (62.5%, SE 2.1%)> these changes were similar in men who became azoospermic to those who did not. The values returned to baseline in the recovery period.
8 men stopped having injections because their partner became pregnant during the suppression phase (table II), despite the agreement to use other forms of contraception at this time. The overall compliance rate with this instruction is unknown. Additionally, a pregnancy in the partner of a man who had stopped having injections because of non-suppression was confirmed two weeks after the last injection> the estimated gestational age was 12 weeks. The outcome of these pregnancies was 5 terminations, 3 healthy live births, and 1 unknown.
Contraceptive efficacy
There was 1 pregnacy during the 1486 months of the efficacy phase (Pearl rate 0.8 [95% confidence interval 0.02-4.5] per 100 person-years). All semen samples in this subject, including those before and after the estimated date of conception, were asoospermic. The pregnancy was terminated. In the efficacy phase (ie, among men who were already azoospermic in at least 3 consecutive specimens), sperm were seen in 21 (1.4% of 1515 samples. These samples were from 11 men--median of 1 non-azoospermic sample per subject (range 1-8)> in no case were injections stopped for spermatogenic rebound, nor did any of the partners of these men become pregnant.
Discontinuations
2 men were discontinued from the study during the efficay phase for protocol violation since they were found on review not to satisfy the admission criteria (female partner aged 36 years, and pre-existing cor pulmonale). A total of 15 men discontinued during the suppression and efficacy phases because of difficulties associated with the injection (annual rate 7.5%)--ie, dislike of the frequency of injections (5), pain (6) or infection (1), at the injection site, or injections not given within the prescribed time interval (3). 52 men also stopped having injections for medical or personal reasons, with annual cumulative rates of 11.9% and 12.7%, respectively. The medical reason (27 men) were acne (9), increased aggressiveness and libido (3), weight gain (2), raised packed cell volume and haemoglobin (2), abnormal lipids (2), hypertension (1), depression (1), tiredness (1), aphthosis (1), acute prostatis (1), pneumonia (1), and Gilbert's syndrome (1)> 2 partners had dysmenorrhoea (1) and unspecified neurological illness (1). There were no discontinuations due to prostatic enlargement, abnormality of liver enzymes, or complaints of reduction in testicular size. Personal reasons (25 men) were unwillingness to continue with the study (10), separation or divorce from partner (9), moving away from the study site (4), or a planned pregnancy (2). 6 men were lost to follow-up, only 1 of whom had entered the efficacy phase.
Recovery
To date, recovery information is available for 230 men (85%)> the sperm concentration of 192 (84%) of these men has returned to 20 million/ml and 106 (46%) to their own baseline level. The median time to recovery to 20 million/ml was 3.7 months (95% CI, 3.6-3.9) in the men who had become azoospermic, 3.0 months (2.8-3.4) in non-suppressors, and 3.9 months (2.9-9.5) among men who discontinued testosterone infections for other reasons. Equivalent data for return to subject's own geometric mean baseline sperm concentration are 6.7 (6.2-8.7), 5.7 (4.0-12.9), and 9.0 (4.6-13.9) months, respectively.
Although only a few couples planned pregnancies after completion of this study, 11 conceptions have been recorded in the recovery phase to date (1 of which was known to be by a man other than the partner). There have been 2 terminations of pregnancy, 1 spontaneous abortion, and 4 normal live births. Partners of the 2 men who stopped receiving injections because the couple planned another pregnancy both became pregnant in the recovery phase.
Discussion
This study has shown that in healthy fertile men rendered azoospermic (as assessed by semen analysis with conventional methods) by weekly injections of testosterone enanthate, this regimen can maintain safe, stable, effective, and reversible contraception for at least 12 months. The contraceptive efficacy in this study was high> it is comparable with typical first-year failure rates of female injectable contraceptives (0.2-0.4 per 100 persons-years)> is better than that of female oral contraceptives (3 per 100 person-years) and IUDs, (6 per 100 person-years)> and is substantially better than of condoms (12 per 100 person-years)--the only available reversible male contraceptive. [18] If the 1 efficacy phase pregnancy (which was possibly "extramarial") was exluded from analysis, the upper 95% CI of the pregnancy rate would be lowered from 4.5 to 3.0 per 100 person-years. Such contraceptive failures are possible in a study of male contraception since the untreated partner becomes pregnant. By contrast, in studies of female contraception, any pregnancy can be directly identified as a contraceptive failure. Pregnancies in the suppression phase can be expected when fertile couples are instructed to change to barrier contraceptive methods. Other methods of inducing azoospermia by the suppression of gonadotropin secretion (eg, gonadotropin-releasing hormone antagonists [19]) might lead to similar patterns of contraceptive efficacy).
The overall safety of testosterone enanthate administration has already been well established during decades of widespread clinical use. [3-5,8] The low rates of discontinuation due to side-effects of the hormone and incidental medical conditions in this study confirms the safety and acceptability of such androgen administration found in studies with up to 18 months exposure. Moreover, the cumulative discontinuation rates for medical events was low and the compliance high in view of the prolonged and demanding nature of the study. The long-term theoretical hazards from the use of androgens might include risks of prostatic and cardiovascular disease. The real hazards remain uncertain and, although the present findings are reassuring in the short term, better quantitative monitoring methods are needed for large-scale surveillance, which would be required to quantify or exclude small risks. The possible long-term benefits from androgen use for bone, muscle, and blood metabolism will also need to be assessed before the nest risk-benefit effects of an androgen-containing regimen can be fully evaluated.
The two major limitations of this regimen are the frequency of injections and the inability uniformly to induce azoospermia. The injection schedule was a major cause for discontinuation, although there was a high rate of compliance by subjects remaining in the study. The maintenance of azoospermia and good contraceptive efficacy was not compromised by a tolerance of 2 days in timing of the weekly injections. The advent of long acting depot testosterone prepations, such as the new WHO-National Institutes of Child Health and Human Development ester 20-AET-1, [20,21] or other testosterone preparations [22,23] which allow androgen administration at intervals of at least 3-4 months would provide a more acceptable method of androgen replacement.
The pronounced heterogeneity in rates of azoospermia between centres is not explained by differences in body size of the men. The lack of a relation between body weight and the likelihood of becoming azoospermic is supported by studies which show that even 50% [24] or greater [8] increases in dose of testosterone enanthate do not cause azoospermia uniformly in Caucasian men. Thus, the use of a fixed androgen dose in centres where there were differences of up to 30% in body weight (20% in BSA) does not explain the different suppression rates. The similar effects of testosterone on body weight gain> rise in haemoglobin> and decrease in plasma urea, LH, and FSH in the suppressors and non-suppressors may indicate that azoospermia is a specific effect of testosterone on spermatogenesis and is not due to variations in testosterone levels, sensitivity to testosterone, or to suppression of gonadotropins. Differences in suppression rates are unlikely to be due to differential rates of compliance with treatment.
This study shows that the laboratory diagnosis of azoospermia corresponds with highly effective contraception, which is rarely followed by resumption of spermatogenesis when regular compliance with hormonal injections is guaranteed. The negligible risk of prenancy in this study implies either than fertile spermatozoa are absent or that those still present in the ejaculate are so few or have such depleted fertilising capacity that conception after intercourse is unlikely. Recent studies have suggested that residual sperm during incomplete suppression of spermatogenesis have decreased fertilising capacity as judged by their ability to penetrate zona-free hamster oocytes. [25,26] Thus, azoospermia many not be necessary for adequate inhibition of male fertility to provide effective contraception and this question is being addressed in the second stage of the study.
* Principal investigators and centres: Dr Zhang Gui-yuan, National Research Institute for Family Planning, Beijing China> Dr Li Guo-zhu, Family Planning Research Institute of Sichuan, chengdu, China> Dr F. C. W. Wu, Centre for Reproductive Biology, Edinburgh, UK> Dr H. W. G. Baker, Prince Henry's Institute of Medical Research, Melbourne, Australia> Dr Wang Xing-hai, Jiangsu Family Planning Institute, Nanjing, china> Dr J. C. Soufir, Universite Paris-Sud, Paris, France> Dr I Huhtaniemi, University of Turku, Turku, Finland> Dr C. A. Paulsen, University of Washington, Seattle, USA> Dr C. Gottlieb, Karolinska Hospital, Stockholm, Sweden> Dr D. J. Handelsman, University of Sydney, Sydney, Australia.
Study and data coordination: Dr T. M. M. Farley, Ms C. Hazelden, Mr A. Peregoudov, Dr G. M. H. Waites, Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organisation, Geneva, Switzerland.
Manuscript prepared by: Dr D. J. Handelsman, University of Sydney Sydney, Australia> Dr T. M. M. Farley, Dr G. M. H. Waites, Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organisation, GEneva, Switzerland.
Correspondence to Dr G. M. H. Waites, Special Programme of Research, Development and Research Training in Human Reproduction, World Health ORganisation, 1211 Geneva 27, Switzerland.
REFERENCES
[1.] Ross JA, Hong S, Huber DH. Voluntary sterilization: an international fact book. New York: Association for Voluntary Surgical Contraception, 1985.
[2.] Maudlin WP, Segal SJ. Prevalence of contraceptive use: trends and issues. Stud Fam Plan 1988> 19: 335-53.
[3.] Rowley MJ, Heller CG. Summary of studies utilizing androgens in the normal human male. Patanelli DJ, ed. Hormonal control of male fertility. US Department of Health, Education and Welfare, Publication No (NIH) 78-1097, 1978: 145-66.
[4.] Paulsen CA, Leonard JM, Burgess EC, Ospina LF. Male contraceptive development: re-examination of testosterone enanthate as an effective single agent. In: Patanelli DJ, ed. Hormonal control of male fertility. US Department of Health, Education and Welfare, Publication No (NIH) 78-1097, 1978: 17-36.
[5.] Swerdloff RS, Palacios A, McClure RD, Campfield RD, Brosman SA. Clinical evaluation of testosterone enanthate in the reversible suppression of spermatogenesis in the human male: efficacy, mechanism of action and adverse effects. In: Patanelli DJ, ed. Hormonal control of male fertility. US Department of Health, Education and Welfare, Publication No (NIH) 78-1097, 1978: 41-63.
[6.] Schearer SB, Alvarez-Sanchez F, Anselmo J, et al. Hormonal contraception for men. Int F Androl 1978> (suppl 2)> 680-712.
[7.] Barfield A, Melo J, Coutinho E, et al. Pregnancies associated with sperm concentrations below 10 million/ml in clinical studies of a potential male contraceptive method, depot medroxy progesterone acetate and testosterone esters. Contraception 1979> 20: 121-27.
[8.] Patanelli DJ. Hormonal control of male fertility. US Department of Health, Education and Welfare, Publication No (NIH) 78-1097, 1978.
[9.] World Health Organisation. Laboratory manual for the examination of human semen and semen-cervical mucus interaction. 2nd ed. Cambridge: Cambridge University Press, 1987.
[10.] Sufi SB, Donaldson A, Jeffcoate SL, eds. Programme for the provision of matched assay reagents for the radioimmunoassay of hormones in reproductive physiology. Method manual. 10th ed. Geneva: World Health Organization, 1986.
[11.] Hunter WM, Bernie JG. Reduction of non-specific serum responses in human pituitary gonadotrophin radioimmunoassays. F Endocrinol 1979> 80: 59O8.
[12.] Bremner WJ, Matsumoto AM, Sussman AM, Paulsen CA. Follicle stimulating hormone and human spermatogenesis. F Clin Invest 1981> 68: 1044-52.
[13.] Corker CS, Davidson DW. A radioimmunoassay for testosterone in various biological fluids without chromatography. F Steroid Biochem 1978> 9: 373-74.
[14.] Matsumoto AM, Paulsen CA, Hopoper BR, Rebar RW, Bremner WJ. Human chorionic gonadotrophin and testicular function: stimulation of testosterone, testosterone, precursors and sperm production despite high estradiol levels. F Clin Endocrinol Metab 1983> 56: 720-28.
[15.] Farley TMMM. Life -table methods for contraceptive research. Stat Medicine 1986> 5: 475-89.
[16.] Gardner MJ, Altman DG, eds. Statistics with confidence: confidence intervals and statistical guidelines. London: British Medical Journal, 1989.
[17.] du Bois, D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med 1916> 17: 863-71.
[18.] Trussell J, Kost K. Contraceptive failure in the United States: a critical review of the literature. Stud Fam Plan 1987> 18: 237-83.
[19.] Weinbauer GF, Khurshid S, Fingscheidt U, Nieschlag E. Sustained inhibition of sperm production and inhibin secretion induced by a gonadotropin-releasing hormone antagonist and delayed testosterone substitution in non-human primates (Macaca fascicularis). F Endocrinol 1989> 123: 303-10.
[20.] Weinbauer GF, Marshall GR, Nieschlag E. New injectable testosterone ester maintains serum testosterone of castrated monkeys in the normal range for four months. Acta Endocrinologica 1986> 113: 128-32.
[21.] Rajalakshmi M, Ramakrishnan PR. Pharmacokinetics and pharmacodynamics of a new long-acting androgen ester: maintenance of physiological levels for 4 months after a single injection. Contraception 1989> 40: 399-412.
[22.] Burris AS, Ewing LL, Sherins RJ. Initial trial of slow-release testosterone microspheres in hypogonadal men. Fertil Steril 1988> 50: 493-97.
[23.] Handelsman DJ, Conway AJ, Boylan LM. Pharmacokinetics and pharmacodynamics of testoterone pellets in man. F Clin Endocrinol Metab 1990> 71: 216-22.
[24.] Matsumoto AM. Effects of chronic testosterone administration in normal men: safety and efficay of high dosage testosterone and parallel dose-dependnt suppression of luteinizing hormone, follicle-stimulating-hormone, and sperm production. F Clin Endocrinol Metab 1990> 70: 282-87.
[25.] Matsumoto AM. Is high dosage testosterone an effective male contraceptive agent? Fertil Steril 1988> 50: 324-28.
[26.] Wu FCW, Aitken RJ. Suppression of sperm function by medroxyprogesterone acetate and testosterone enanthate in steroid male contraception. Fertil Steril 1989> 51: 691-98.
