Comparative studies of prostaglandins F 2α and E 2 in late cyclic and early pregnant sheep: [formula omitted] synthesis by endometrium and conceptus effects of [formula omitted] indomethacin treatment on establishment of pregnancy

Abstract

Endometrial concentrations of prostaglandins F 2α (PGF 2α) and E 2 (PGE 2) were measured by specific radioimmunoassay in sheep, on day 14 of estrous cycle or pregnancy, during luteolysis (Day 16 of the cycle), and after implantation (Day 23 of pregnancy) : concentrations observed on day 14 of cycle and pregnancy were similar. During luteolysis, on day 16 of cycle, a consistent drop was noticed. If luteal regression did not occur, as a consequence of the presence of an embryo, endometrial concentrations of PGF 2α on day 23, were twice those of day 14, and PGE 2 remained unchanged. In vitro 2 hour incubations of endometrial caruncular tissue from 14 days cyclic or pregnant ewes resulted in de novo synthesis of PG which could be increased by Arachidonic Acid and inhibited by Indomethacin; during the first 30 min of incubation, the PGF 2α synthesis was comparable for both endometrial tissues, whereas PGE 2 synthesis was twice as great in pregnant endometrium. Fourteen and 23 day conceptuses had high PGF 2α and PGE 2 concentrations which were not due to maternal PG sequestration : de novo PG synthesis which could be inhibited by Indomethacin was observed in incubated 14 day old embryos. Treatment of pregnant ewes from day 7 to day 22 after mating, either with Indomethacin (300 mg s.c. daily) or with Acetylsalicylic Acid (1 g I.V. daily) resulted in a sharp diminution of endometrial PG concentration and release, with no apparent effect on the establishment of pregnancy. These results tend to ascribe a less important role to PG during early pregnancy in sheep as compared with rodents, in terms of embryonic growth and implantation.