Maintenance of the Corpus Luteum of Early Pregnancy in the Ewe. II. Prostaglandin Secretion by the Endometrium in vitro and in vivo1

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Abstract
To determine if the synthesis and/or secretion of prostaglandins PGF2α and PGE2 differed during the late luteal phase of the cycle and early pregnancy, a combination of in vivo and in vitro parameters were studied. Synthesis of PGF2α and PGE2 by ovine endometrial tissue in vitro was studied on Days 13, 15 and 17 of the estrous cycle and pregnancy. The prostaglandins were quantified by radioimmunoassay. There was no difference in the quantity of PGF2α synthesized by tissue collected on Day 13 of either the cycle or pregnancy. Synthesis of PGF2α was greater on Day 15 (P2 was also significantly greater on Days 15 (P<.001) and 17 (P2α and PGE2 in endometrial tissue followed the same pattern as in vitro secretion, suggesting that in vitro secretion accurately reflects the in vivo capacity of endometrial tissue to synthesize PGs. Concentrations of PGF2α in uteroovarian venous serum were greater on Day 13 (P2 in uteroovarian venous serum were greater on Days 15 (P2α was present in uterine flushings in extremely small quantities (0.3-0.6 ng/ml) and PGE2 was nondetectable (2α and PGE2 were relatively high on all days of pregnancy examined and on Day 15 were at least 50 times greater than on Day 15 of the estrous cycle.