Androgens

The male gonads (more precisely, the interstitial cells or the cells of Leydig in the testes) and, to a lesser extent, the adrenal cortex (secretes androstenedione and dehydroepiandrosterone that are converted in the periphery to testosterone or estrogen) produce the male sex steroids known as androgens, the secretion of which is controlled by the hypothalamic-pituitary-testicular axis. The hypothalamus secretes gonadotrophin-releasing hormone (GnRH), which is sometimes referred to as luteinizing hormone-releasing hormone (LHRH), and this in turn stimulates the release of the gonadotrophins (follicle-stimulating hormone and luteinizing hormone; sometimes referred to as interstitial cell stimulating hormone in the male), which control gonadal function, including steroidogenesis. Testosterone levels then influence the hypothalamic-pituitary-testicular axis by means of a negative feedback loop. Sex steroids influence the development and maintenance of the organs and tissues, directly and indirectly associated with reproduction. Testosterone is the main androgenic hormone formed in the interstitial cells of the testes. However, in many of the androgen target tissues, testosterone has to be converted to the more active dihydrotestosterone, by 5alpha-reductase. Androgens stimulate the development of the male secondary sex characteristics, for example, male body hair distribution and lengthening of the vocal cords, as well as regulating gonadal function. Androgens also possess anabolic properties (removal of the 19-methyl group may enhance this particular attribute, e.g., nandrolone) as they increase the retention of nitrogen, sodium calcium, potassium, chloride, and phosphate. This causes an increase in water retention and bone growth. Skin also tends to become more vascular (and less fatty), and erythropoiesis is stimulated.