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Factors produced by bovine conceptuses alter prostaglandin (PG) and protein secretion by endometrial explants from cyclic cows and induce an intracellular inhibitor of PG synthesis. Endometrial explants from cyclic (n = 4) and pregnant (n = 3) cows at Day 17 following estrus were incubated for 24 h with 0, 0.1, 0.5, 1 and 5 microg platelet-activating factor (PAF)/ml. Cotyledonary microsomes from parturient cows were utilized to determine levels of an intracellular/cytosolic inhibitor of PG synthesis. Endometrial explants from additional cyclic cows (n = 4) were incubated for 24 h with 0 or 5 microg PAF/ml with and without 50 microCi [(3)H]leucine. Endometrial explants (cyclic cows, n = 3) were also incubated for 12 h with each of the following treatments: 1) Control; 2) PAF (1 microg/ml); 3) lyso-PAF (2 to 10 microg/ml); 4) PAF-receptor antagonist (2 to 10 microg/ml); 5) PAF (1 microg/ml) + antagonist (2 to 10 microg/ml); 6) bovine conceptus secretory proteins (bCSP; 25 microg/ml); and 7) bCSP (25 microg/ml) + antagonist (5 microg/ml). Platelet-activating factor had distinct negative and positive dose effects on PGF and PGE-2 secretion, respectively, by explants from cyclic cows, whereas PG secretion was not altered by PAF in the endometrium of pregnant cows. Platelet-activating factor did not alter the level of an intracellular inhibitor of prostaglandin synthesis, whereas, bCSP increased the level of this inhibitor. Platelet-activating factor decreased the incorporation of [(3)H]leucine into tissue and secreted proteins for explants from cyclic cows. Lyso-PAF did not alter endometrial prostaglandin secretion. The effects of PAF but not of bCSP were blocked by the PAF-receptor antagonist. Platelet-activating factor altered PG and protein secretion by the endometrium from cyclic cows, and it may be a potential regulatory factor during early pregnancy if secreted by the bovine conceptus.

Maternal heat stress in cattle may disrupt pregnancy by elevating uterine prostaglandin F(2 alpha) (PGF(2 alpha)) secretion. The objectives of this study were to determine the effects of elevated temperature (42 degrees C) in vitro upon 1) prostaglandin secretion by endometrial tissue; 2) the actions of extracellular regulators of uterine PGF [conceptus secretory proteins (bCSPs) and platelet-activating factor, (PAF)]; 3) the activity of the cyclooxygenase-endoperoxidase enzyme complex (PG synthetase); and 4) the activity of the endometrial PG synthesis inhibitor present in the endometrium from pregnant cattle. Endometrial explants at Day 17 of the estrous cycle produced more PGF than PGE(2) while elevated temperature caused increased PGF secretion but did not affect PGE(2) secretion. Elevated temperature did not reduce the ability of bCSPs or PAF to suppress release of PGF. The heat shock-induced increase in PGF at Day 17 was not due to the direct effects on PG synthetase, because PGF production from a cell-free cotyledonary microsomal enzyme preparation was reduced at elevated temperature. The activity of the cytosolic inhibitor of cyclooxygenase present in the endometrium of Day-17 pregnant cows could be reduced but not eliminated at 42 degrees C. We conclude that in vitro heat stress induces PGF secretion from the bovine uterine endometrium at Day 17 after estrus. This increase is not accompanied by the loss of regulatory capacity of conceptus products or increased activity of PG synthetase.