Effects of estradiol and progesterone on uterine prostaglandin levels in the pregnant rat.

The purpose of this study was to delineate the effects of estradiol and progesterone treatment on uterine prostaglandin F (PGF), PGE, Thromboxane B2 (TxB2) and 6-Keto-PGF1 alpha (6KF) levels in the pregnant rat. Rats were ovariectomized on day 19 of pregnancy (sperm in vagina = day 0) and received the following treatments via silastic inserts placed s.c.: controls; estradiol (E); progesterone (P); estradiol + progesterone (EP). Twenty-four hours later (day 20 of pregnancy) uterine venous blood and uterine tissue were obtained and assayed for PGE, PGF, TxB2 and 6KF by radioimmunoassay. E treatment significantly enhanced (p less than .05) uterine PGF, TxB2 and PGE (4.5, 2.8 and 1.8 fold increase, respectively) but did not alter 6KF levels when compared to C. Concomitant administration of P with E (EP) blocked the stimulatory effects of estradiol. P treatment by itself was ineffective. Steroid treatment induced no significant alterations (p greater than .05) in uterine venous plasma PG levels. These results suggest that estradiol can provoke a dramatic increase in uterine PGF, TxB2 and PGE levels in the pregnant rat but has no effect on net production of 6KF. These data are compatible with the hypothesis that an increase in the ratio of E/P at the end of pregnancy in the rat contributes to enhanced uterine concentrations of PGF, TxB2 and PGE at term, but they do not explain the augmented 6KF concentrations reported at parturition.