The male hypothalamic-pituitary-gonadal (HPG) axis is a finely controlled system whose role is to promote spermatogenesis and androgen biosynthesis. Testosterone is thought to feed back to restrain activity of the gonadotropin-releasing hormone (GnRH)-gonadotrope secretory unit. GnRH is released from the hypothalamus in a pulsatile pattern, and the stimulation of gonadotropin biosynthesis and secretion by GnRH is dependent on the pulsatile nature of GnRH delivery to the anterior pituitary. Gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are glycoproteins consisting of a common a subunit and a hormone-specific β subunit that are associated through noncovalent interactions. GnRH stimulates in vitro the synthesis of gonadotropin subunits and increases a, LH-β, and FSH-β subunit mRNA levels as well as the transcriptional activity of corresponding gene promoters. Testosterone seems to exert a direct feedback control of LH secretion, while its action on FSH secretion is mostly indirect.