Biochemical and Physiological Aspects of Endogenous Androgens

Abstract

This review attempts to give a synopsis of the major aspects concerning the biochemistry of endogenous androgens, supplemented with several facets of physiology, particularly with respect to testosterone. Testosterone continues to be the most common adverse finding declared by World Anti-Doping Agency accredited laboratories, such samples having an augmented testosterone to epitestosterone ratio. Knowledge regarding the precursors and metabolism of endogenous testosterone is therefore fundamental to understanding many of the issues concerning doping with testosterone and its prohormones, including the detection of their administration. Further, adverse findings for nandrolone are frequent, but this steroid and 19-norandrostenedione are also produced endogenously, an appealing hypothesis being that they are minor by-products of the aromatization of androgens. At sports tribunals pertaining to adverse analytical findings of natural androgen administration, experts often raise issues that concern some aspect of steroid biochemistry and physiology. Salient topics included within this review are the origins and interconversion of endogenous androgens, the biosynthesis of testosterone and epitestosterone, the mechanism of aromatization, the molecular biology of the androgen receptor, the hypothalamic-pituitary-testicular axis, disturbances to this axis by anabolic steroid administration, the transport (binding) of androgens in blood, and briefly the metabolism and excretion of androgens.

Drug-drug interactions and masking effects in sport doping: influence of miconazole administration on the urinary concentrations of endogenous anabolic steroids

“…This effect was ascribed to the inhibition of the 17a-hydroxylase and 17, 20-lyase activities of CYPC17 (conversion of pregnenolone to DHEA and progesterone to ASD) [40], but recent studies have also shown its inhibitory potential on steroid glucuronidation in vitro [13,16]. Figure 1 schematizes androgen biosynthetic and excretion metabolic pathways and underlines the sites of metabolic modulations by ketoconazole and finasteride [41].…”

Hormonal profile, the PROGINS polymorphism, and erectile dysfunction complaints: data from a population-based survey

“…T has been clearly linked to behavior and sexual function in men (7,35), with influence on sexual desire, sexual thoughts, the intensity of sexual feelings, and sexual activity (36,37). Studies using animal models have also described a decrease in T concentration and a higher frequency of erections in sleep-deprived rats (8)(9)(10).…”

Testosterone restores respiratory long term facilitation in old male rats by an aromatase‐dependent mechanism

“…In the present study, by supplementing old rats with ‘new’ testosterone, more bioavailable (free) testosterone may have been produced in the circulation. Additionally, as high androgen levels are known to decrease SHBG (Plymate et al 1983; Selby, 1990; Kicman, 2010), abruptly raising serum testosterone levels may have also resulted in a greater local proportion of bioavailable testosterone that contributed to the restoration of XII LTF and enhancement of phrenic LTF.…”