Alterations in uterine and placental prostaglandin F and E with gestational age in the rat

Abstract

Experiments were designed to determine the chronological alterations in placental and uterine prostaglandin F and E (PGF and PGE) during pregnancy in the rat. Pregnant rats (sperm in the vagina = day 0) were sacrificed at days 15, 18, 19, 20, 21 and delivery (day 21 1/2) and placental and uterine tissues assayed (RIA) for PGF and PGE immediately ("in vivo") or after 1 hour incubation ("in vitro"). Uterine content of PGF and PGE in vivo (ng Pg/mg DNA) was increased significantly by day 19 and further increases were seen through delivery. Incubation of uterine tissue resulted in enhanced net production of PGF and PGE (p less than .05) per mg DNA (as judged by tissue content and release into the incubation medium) by day 18 of pregnancy vs. day 15. Net production in vitro peaked around the time of delivery thus paralleling the alterations in tissue content in vivo. By contrast, no differences with gestational age were found in placental content of PGF and PGE in vivo, the concentrations throughout late gestation remaining in the range of uterine PGs at day 15. However, production of PGs per mg placental DNA increased markedly during incubation in vitro with significant enhancement detected by day 19 vs. 15, achieving levels even greater than the uterus in vitro. The in vivo and in vitro findings for the uterus are consistent with the hypothesis that increases in uterine PGs levels at the end of pregnancy may play an important role in parturition. The in vitro experiences with placental tissue suggest that the potential for PG production per placental cell may also increase in late gestation and thereby contribute to the augmented intrauterine availability of PGs at that time.