Reduction by human chorionic gonadotropin of the luteolytic effect of prostaglandin F 2 α in ewes

Abstract

The ability of human chorionic gonadotropin (HCG) to reduce the luteolytic effect of prostaglandin (PGF 2 α ) was demonstrated in cycling ewes. As expected, treatment with 10 mg of PGF 2 α alone on Day 10 of the estrous cycle exerted a potent negative effect on the function and structure of corpus luteum (CL) as indicated by reduced plasma progesterone, CL progesterone, and CL weight. However, the identical PGF 2 α treatment failed to significantly reduce either luteal function or luteal weight when administered to ewes that were also treated with HCG on Days 9 and 10 of the estrous cycle. Treatment with HCG alone had a positive effect on CL as indicated by increased plasma progesterone, CL progesterone, and CL weight. Treatment with HCG did not render the CL totally insensitive to the negative effects of PGF 2 α because plasma progesterone was reduced when the dose of PGF 2 α was doubled. Whether CL regressed or continued to function after treatment with both HCG and PGF 2 α appeared to depend upon a balance between the positive and negative effects of the two hormones.