| Abstract: | The mechanism of the postcoital contraceptive effect of luteinizing hormone-releasing hormone (LH-RH) was studied in the rat. 200 mcg of LH-RH administered daily over Days 1-7 of pregnancy produced a dramatic inhibition of pregnancy. This inhibition was directly correlated with induced 'surges' in serum LH over Days 1-4. Serum follicle stimulating hormone and prolactin were, in general, reduced over this same time period. A 48-hour delay in the preimplantation (Day 3) 'surge' in serum estradiol accompanied by a significant (ps less than .05 and less than .01) reduction in serum progesterone on Days 3, 4, 6, and 7 was also observed. The delayed 'surge' in serum estradiol on Day 5 and reduction in serum progesterone was correlated with an increase in folliculogenesis and luteolysis of established corpora lutea, respectively. These data suggest that in the rat LH-RH induces a rise in serum LH which is luteolytic during pregnancy and delays the serum estradiol surge necessary for normal implantation. |
