Anabolic steroids combine with the same receptors as testosterone. The secretion of testosterone is controlled using the negative feedback loop illustrated. Administering anabolic steroids makes the hypothalamus and anterior pituitary believe that testosterone levels in the blood are excessively high. They therefore reduce the production of GnRH, FSH and LH. FSH is the hormone that stimulates the production of sperm in the Sertoli cells in the testes. The Sertoli cells also contribute the vast majority of testicular volume, so decreased FSH production will decrease Sertoli cell, and therefore testicular, volume. LH is the hormone that stimulates the Leydig cells to produce testosterone, so reducing LH levels in the blood will decrease testosterone production.