Inhibitory Effect of a Luteinizing Hormone (LH)-Releasing Hormone Agonist on Rat Ovarian LH and Follicle-Stimulating Hormone Receptor Levels During Pregnancy

When injected at the daily dose of 100 μg on days 7 through 12 of pregnancy, the luteinizing hormone (LH)-releasing hormone (LHRH) agonist [D-Ala 6 ,des-Gly- NH 2 10 ] LHRH ethylamide led to complete suppression of pregnancy and a 45% to 60% decrease in plasma progesterone concentration. The antifertility effect of the LHRH analog was accompanied by an early and almost complete inhibition of ovarian LHlhuman chorionic gonadotropin and follicle-stimulating hormone receptor levels. These data suggest that the antifertility effects of LHRH agonists are mediated by down-regulation of ovarian gonadotropin receptors and decreased luteal function.