I have found tremendous anecdotal evidence of such. You can find it at:
http://www.steroidology.com/forum/forumdisplay.php?f=4
I reject the claim that gyno from deca or tren is due simply to the ratio of E to T+DHT because estrogen induced gynecomastia doesn't come with lactation. Furthermore, the problem typically resolves with administration of vitamin B6, Bromo or Dostinex. Thus, I am confident that prolactin is high.
It would be very interesting to see a blood test for:
prolactin
estradiol for men
total estrogens
From one of these guys taking only deca or tren but that is lactating. But I haven't seen such as of yet, so oh well.
Can prolactin gyno occur without the prescence of estrogen? Probably not, but I do think that it can and does occur in the presence of
normal levels of estradiol.
Now, with all of that said, I certainly can not say with much certainty how the deca and trenbolone cause an increase in prolactin, so perhaps I went too far in my statement. I, like others, have speculated that their progestin activity somehow stimulates the prolactin release. But perhaps there is an action unknown, such as stimulating the prolactin receptors (?) directly.
In searching through google, it seems like there might be evidence that, at least in the case of pregenant women, progesterone goes up which stimulates prolactin which is necessary to get the milk going for the baby. But I haven't done enough research. I apparently haven't found very good keywords to find the best articles.
One problem we have is that there aren't a lot of studies on men using deca or trenbolone.