MALE REPRODUCTIVE HORMONES AND THEIR CONTROL
The hormones are secreted by Leydig and Sertoli cells in the testes. Leydig cells produce testosterone, which is controlled by luteinizing hormone (LH) or interstitial cellstimulating hormone (ICSH).
Low levels of testosterone cause an increase in LH secretion by the anterior pituitary. The increase in LH secretion causes the Leydig cells in the testes to secrete testosterone. Increased testosterone inhibits the further secretion of LH, and testosterone levels are thus stabilized and the cycle is repeated; this is known as a negative feedback system. Testosterone must diffuse into the seminiferous tubules from the interstitial tissues in order to affect spermatogenesis. It appears that testosterone supports the meiotic process within the seminiferous tubules, hence maintaining spermatogenesis.Sertoli cells are stimulated by follicle-stimulating hormone (FSH) and produce androgen-binding protein. The androgen-binding protein is secreted into the lumen of the seminiferous tubules and binds with testosterone and other androgens to stabilize their concentrations and ensure appropriate amounts for spermatogenesis. It is also believed that FSH stimulates the secretion of estrogens by the Sertoli cells. The actual secretion of estrogen might arise from the intracellular conversion of testosterone (originating from Leydig cells) by the Sertoli cells. The Sertoli cells also secrete a hormone known as inhibin, which inhibits the secretion of FSH by the anterior pituitary. FSH is not necessary for the maintenance of spermatogenesis once it has begun, but LH is constantly needed for spermatogenesis (testosterone-supported meiosis). FSH is essential for the initiation of spermatogenesis throughout puberty and following physiological or pathologic disruptions.
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