Neuroendocrine control of human testicular function

Abstract

The proximate regulator of testicular function is gonadotropin-releasing hormone (GnRH) produced in neurons scattered throughout the anterior hypothalamus. When it reaches the anterior pituitary, GnRH stimulates the synthesis and secretion of the pituitary gonadotropic hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH are released into the circulation in bursts and activate G-protein coupled receptors on Leydig and Sertoli cells, respectively, that stimulate testosterone production and spermatogenesis. The system is tightly regulated and is maintained at a proper set-point by the negative feedback effects of testicular steroids and inhibin-B. Testicular function is also influenced by multiple internal (paracrine and autocrine) and external (endocrine) environmental factors.