Testosterone is principal male androgen, sex hormone and anabolic steroid. It is found not only in humans, but also in many other vertebrates. In males, testosterone is secreted by Leydig cells in testicles, in females by theca cells in ovaries. Small amount is produced also in zona reticularis of adrenal cortex in both genders and in placenta. Chemically (figure 1), it is white powder, soluble in methanol, name is17beta-Hydroxyandrost-4-en-3-on or 4-An-drosten-17beta-ol-3-on, Chemical Abstracts Service number 58-22-0, ATC code G03BA03. It is a controlled substance, in US by Drug Enforcement Administration (DEA). It's inactive epimer - difference in configuration of OH at C17 - is called epitestosterone. Testosterone's biosynthesis starts from cholesterol. Metabolism: up to one tenth of testosterone is converted by 5-alpha reductase to dihydrotestosterone, less than 0.5% by aromatase to estradiol. Most of testosterone is deactivated and excreted as glucoronides.
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