Testes Testosterone is the principle hormone of the testes and is synthesized from cholesterol by the Leydig cells. The secretion of testosterone is under the control of LH from the pituitary. LH secretion is decreased by increased levels of testosterone in the blood via negative feedback. Testosterone develops and maintains the male secondary sex characteristics, is anabolic and growth promoting and participates in the formation of sperm. It also causes aggressive behavior and increased libido.
Body hair is increased by androgens while scalp hair is decreased.
Like other steroids, testosterone enters cells and binds to an intracellular receptor and then causes the production of mRNA coding for proteins that manifest the changes induced by testosterone. In some target tissues a form of testosterone, DHT, is produced that has greater stability in combination with the receptor and therefore produces a longer lasting effect. DHT is needed for the maturation of the accessory glands and external genitalia, while testosterone is more important in the growth of muscle mass, development of the internal genitalia and maintainence of the male libido and sex drive. Another hormone produced by the testes is the polypeptide hormone, inhibin, produced by the Sertoli cells. It inhibits FSH secretion by a direct action on the pituitary.