Androgen physiological effects

Steroid hormones are divided into six classes, based on physiological effects estrogens, androgens, progestins, glucocorticoids, mineralocorticoids and vitamin D 847... 

Male and female hormones are produced primarily in the gonads. Androgens are synthesized in the testes in the male. In the female, the ovaries are the principal sites of estrogen and progestin production. As discussed in Chapter 29, small amounts of sex-related hormones are also produced in the adrenal cortex in both sexes, which accounts for the fact that small amounts of hormones of the opposite sex are seen in females and males that is, low testosterone levels are seen in females, and males produce small quantities of estrogen. However, under normal conditions, the amounts of sex-related hormones produced by the adrenal cortex are usually too small to produce significant physiologic effects. 

In adult males, testosterone is the principal androgen produced by the testes.39,40,144 Testosterone is synthesized by Leydig cells located in the interstitial space between the seminiferous tubules (Fig. 30-1). The seminiferous tubules are the convoluted ducts within the testes in which sperm production (spermatogenesis) takes place. Testosterone produced by the Leydig cells exerts a direct effect on the seminiferous tubules, as well as systemic effects on other physiologic systems (see Physiologic Effects of Androgens ). 

In addition to their structural similarities, adrenocorticoids, estrogens, progestins, and androgens share a common mode of action. They are present in the body only in extremely low concentrations (e g., 0.1-1.0 nM), they exert potent physiologic effects on sensitive tissues, and they bind with high affinity to intracellular receptors. Extensive research activities directed at elucidation of the general mechanism of steroid hormone action have been performed for several decades, and many reviews have appeared (2,3,4,5,6,7). 

The overall physiological effects of endogenous androgens are contributed by testosterone and its... 

Androstenolone. d ydroepiandrosterone, 3fi-hy-dmxyattdrosl-S-ene-17-dione an androgen less potent than testosterone, but with similar physiological effects. It is an intermediate in the biosynthesis of testosterone in the adrenal cortex. For structure and biosynthesis, see Androgens. 

Our data have shown that the non-aromatlsable androgen DHT and progestins can act directly at the pituitary level at physiological concentrations to inhibit spontaneous PRL secretion and reverse the well-known stimulatory effect of E (39, 40, 42, 51). In addition, the effect of E2, DHT and progestins is observed, not only on spontaneous and IRH-induced PRL secretion, but also in the presence of IBMX. This last observation suggests that the marked modulatory effects of sex steroids are exerted at a step following cyclic AMP formation. 

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