Trophoblastin, an antiluteolytic protein present in early pregnancy in sheep

Abstract

Trophoblastin, an antiluteolytic component from the embryo, was identified in the ewe by intrauterine injections of homogenates from trophoblasts at 14-16 days pregnancy. Homogenates from embryos and their membranes at 21-23 days pregnancy did not extend the life of the corpus luteum [CL], suggesting that trophoblastin synthesis occurs for only a short period. The trophoblastin was thermolabile (80.degree. C for 30 min) and inactivated by pronase. Treatment of ewes with oCS [ovine chorionic sommato mammotrophin], hCG [human chorionic gonadotropin] and extracts of 120-day placentae did not affect the time of luteolysis. The protein appears to be insoluble at pH 7 or 8, but to dissolve readily at pH 9.6. After injection of homogenates or extracts from 14-16 day old trophoblasts, the initial CL were maintained for > 1 mo. in most cyclic recipient ewes. Surgical removal of embryos at 21-23 days resulted in luteal maintenance for > 1 mo. in > 50% of the operated animals. All the maintained CL were secretory although their average wt was about 1/2 of that CL of normal pregnancy, suggesting the existence of complementary luteotrophic placental factors. The uteri of most of these pseudopregnant ewes were distended with a clear, sterile fluid.