Source and Regulation of Androgen Synthesis

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 ). 

for example, increases the expression of a polypeptide known as androgen-binding protein (ABP). ABP helps concentrate testosterone within the seminiferous tubules and helps transport testosterone to the epididymis.39 FSH may also affect Leydig cell function indirectly by increasing the production of other chemical messengers from the Sertoli cells that enhance differentiation and function of Leydig cells.146 147 

Therefore, both pituitary gonadotropins are required for optimal androgen function. LH acts on the Leydig cells to stimulate testosterone synthesis, 

Release of the pituitary gonadotropins (LH, FSH) is regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus.21,144 A classic 

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