Suppression of meiosis of male germ cells by an antagonist of luteinizing hormone-releasing hormone.

Male nude mice were implanted with osmotic minipumps releasing 50 micrograms of a potent antagonist of luteinizing hormone-releasing hormone (LH-RH) per day [N-Ac-[D-Nal(2)1,D-Phe(pCl)2,D-Pal(3)3,D-Cit6,D-Ala10]LH-RH] (SB-75) [Nal(2), 3-(2-naphthyl)alanine; Phe(pCl), 4-chlorophenylalanine; Pal(3), 3-(3-pyridyl)alanine; Cit, citrulline], or they were treated with s.c. injections of SB-75 (25 micrograms twice a day). Another group of nude mice received an injection of microcapsules of the agonist [D-Trp6]LH-RH liberating 25 micrograms/day. One month after the initiation of treatment, the testicular weights were significantly reduced and the blood testosterone values were at castration levels in all treated groups. Histologically, only the testicles of the mice treated with SB-75 released from minipumps showed a significant decrease of meiosis. The most advanced forms of germ cells were spermatogonia in 26%, spermatocytes in 17%, and round spermatids in 35% of the seminiferous tubules. Only 22% of the tubules contained elongated spermatids. The suppression of meiotic activity by this modern LH-RH antagonist can possibly be used for the development of methods for male contraception and for the protection of germ cells against the damage caused by cytotoxic drugs and x-radiation.