i did 8 years of Judo, and competed.
like biggin said, your body will release that adrenaline, you just need to get used to it.
spar spar spar, get on the mat as much as you can. and after that, competition is still a whole other story, you just have to keep at it, and your body will adjust.
lets put it this way, 5years into doing judo, i had to have a minor surgery, they actually gave me an adrenaline shot to control bleeding, because when you get hit with adrenaline all the blood rushed to heart... i didnt even feel a rush, just so used to it.