Inhibitory Effect of LHRH and Its Agonists on Testicular Gonadotrophin Receptors and Spermatogenesis in the Rat

Treatment of adult male rats with the potent LHRH agonists [D‐Leu6, des‐Gly‐NH210]LHRH ethylamide or [D‐Ala6. des‐Gly‐NH210]LHRH ethylamide led to a marked reduction of testicular LH and prolactin receptor levels accompanied by decreased plasma testosterone levels and testis, seminal vesicle and prostate weight. Maximal inhibitory effects were seen at a dose of 50 ng. After a single injection, maximal inhibitory effects were seen at 2–4 days with return toward normal levels at later time intervals. Similar results were obtained with LHRH itself although 5 μg was required for maximal effects. When the LHRH analog was administered twice a week at the 100 ng dose, degenerative signs appeared in the seminiferous tubules after one week while at four weeks, degenerative changes were so advanced that almost all germ cells had disappeared leaving only Sertoli cells.