Biology of Reproduction, Vol 21, 845-856, Copyright © 1979 by Society for the Study of Reproduction

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

¹ Department of Physiology and Biophysics, Colorado State University, Fort Collins, Colorado 80523

To determine if the synthesis and/or secretion of prostaglandins PGF₂ 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 PGF₂ 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 PGF₂ synthesized by tissue collected on Day 13 of either the cycle or pregnancy. Synthesis of PGF₂ was greater on Day 15 (P<0.01) and tended to be greater on Day 17 (P<0.10) of pregnancy than on Day 15 or 17 of the estrous cycle. Synthesis of PGE₂ was also significantly greater on Days 15 (P<.001) and 17 (P<0.05) of pregnancy than on the same days of the estrous cycle. Synthesis rates of both PGs in vitro tended to decrease from Days 13-17 in tissue collected from cycling ewes, while increasing from Days 13-15, then falling again on Day 17 of pregnancy. Concentrations of PGF₂ 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 PGF₂ in uteroovarian venous serum were greater on Day 13 (P<0.05) and not different on Days 15 and 17 of pregnancy compared with the same days of the estrous cycle. However, concentrations of PGE₂ in uteroovarian venous serum were greater on Days 15 (P<0.01) and 17 (P<0.05) of pregnancy than on the same days of the estrous cycle. Prostaglandin F₂ was present in uterine flushings in extremely small quantities (0.3-0.6 ng/ml) and PGE₂ was nondetectable (<10 pg/ml) on Days 13, 15 and 17 of the estrous cycle. In contrast, concentrations of PGF₂ 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.

Note:
ACKNOWLEDGMENTS The authors wish to thank Vaughn Cook for his expert assistance during the course of these studies.

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