Epitestosterone--a hormone or not

Epitestosterone is a natural component of biological fluids of several mammals including man. For a long time it has been believed that it is a metabolite without any hormonal activity and without any marked relationship to the hormonal state in health and disease. The biosynthetic pathway as well as the site of its formation in man has not been unequivocally confirmed until now. It apparently parallels the formation of testosterone but, on the other hand, its concentration is not influenced by exogenously administered testosterone. This fact creates the basis of the present doping control of testosterone abuse. In 1989 an observation was presented in a dermatological study that epitestosterone has an effect counteracting the action of testosterone on flank organ of Syrian hamster. Further studies showed that a complex action consisting of competitive binding of epitestosterone to androgen receptor, of inhibition of testosterone biosynthesis and its reduction to dihydrotestosterone and of antigonadotropic activity could be demonstrated in rat, mice and human tissues. It can be presumed that epitestosterone as a natural hormone can contribute to the regulation of androgen dependent events as e.g. to the control of growth of prostate or body hair distribution.