Starka, L. (2003). Epitestosterone. Journal of Steroid Biochemistry and Molecular Biology, 87, 27-34.

"Epitestosterone has been identified as a natural component of biological fluids of several mammals including man. For a long time it was believed that it is a metabolite without any hormonal activity and without any marked relationship to the hormonal state in health and disease. Neither the biosynthetic pathway nor the site of its formation in man have been unequivocally confirmed to date. It apparently parallels the formation of testosterone (T), but on the other hand its concentration is not influenced by exogenous administration of 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 exerts 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 such androgen dependent events as, e.g. the control of prostate growth or body hair distribution".

Implication. Epitestosterone has to be developed through some form of stimulation. If it is increased or decreased under certain circumstances, the reliability of the T:ET ratio in drug testing has to be questioned. Although it is not influenced by exogenous testosterone administrations, its stability in humans, and therefore its potential as an absolute marker for comparison of testosterone concentrations, has not been established. This is but one more assumption made for drug-testing for which supporting evidence is unavailable.

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