Inhibition of Prostaglandin F 2α or LH Induced Luteolysis in the Pseudopregnant Rabbit by 17β-Estradiol 1

Abstract

Summary

Administration of prostaglandin F_2α (PGF_2α) or luteinizing hormone (LH) induces luteolysis in the rabbit. The present study was designed to compare the effect of estrogen treatment on the luteolytic action of PGF_2α and LH in pseudopregnant Dutch Belted rabbits. PGF_2α (500 μg administered subcutaneously twice a day on days 9 through 12 of pseudopregnancy) reduced (p < .001) corpora lutea weights by day 14 and lowered peripheral plasma progestin levels on days 11 (p < .001) and 14 (p < .05). LH (50 μg intravenously on day 9) comparably reduced corpora lutea weights although plasma progestin levels increased due to LH-induced ovulations. In animals receiving 17β-estradiol (20 μg/day subcutaneously on days 9 through 12) plus LH, corpora lutea weights did not differ significantly from controls. Corpora lutea in rabbits receiving 17β-estradiol plus PGF_2α were heavier (p < .05) than in animals receiving PGF_2α alone but less (p < .05) than controls. This luteo-tropic effect of estradiol was also reflected by the presence of significant (p < .05) plasma progestin concentrations on days 11 and 14. A 5-fold increase in the dose of PGF_2α did not completely overcome the luteotropic effect of 17β-estradiol.