Gonadotropin-releasing hormone from the hypothalamus is released in the portal system in order to reach the gonadotropic cells in the pituitary. Upon stimulation, these cells release FSH and LH. The Leydig cells in the testis carry receptors for LH. LH promotes the production of testosterone in these cells. Testosterone serves three main functions: it stimulates Sertoli cells and, when present in the bloodstream it has a negative feedback on GnRH and LH secretion and it serves general functions in most body cells such as development of secondary sex characteristics and increase of muscle mass.
The Sertoli cells are stimulated by FSH and testosterone from the Leydig cells and produce nutrients and growth factors for the maturation of the sperm cells. The Sertoli cells also produce inhibin, which has a negative feedback on the pituitary FSH.
I LH stimulates the Leydig cells to produce testosterone and FSH stimulates the Sertoli cells to produce sperm cells. II Inhibin decreases secretion of FSH and LH by inhibiting GnRH secretion.
Extra info: Inhibin is an inhibitor of FSH synthesis and secretion.