Regression of corpora lutea in the rabbit after injection of a gonadotropin-releasing peptide.

We have shown that a potent agonist of the luteinizing hormone injected on either Day 11 of pseudopregnancy of Day 15 of pregnancy causes luteinization of ovarian follicles and a rapid regression of functional corpora lutea. Serum levels of progesterone declined markedly within 3 days of peptide injection in pregnant animals. In the presence of regressing corpora lutea, fetal resorption occurs which can be prevented by estradiol (500 ng, twice a day) or progesterone. Daily levels of estradiol below 4 mug did not maintain either corpora lutea weight or fetal survival, whereas 4 mug of the steroid maintained corpora lutea weight, but not pregnancy.