Mechanisms Regulating Prostaglandin F₂ Secretion from the Bovine Endometrium

¹ Department of Animal Sciences and Center for Reproductive Biology, Washington State University, Pullman 99164-6353
² Department of Dairy and Poultry Sciences, University of Florida, Gainesville 32611
³ Animal Science Department, Texas A&M University, College Station 77843-2471

The mechanism that regulates luteolytic PGF₂ secretion as stimulated by oxytocin is thought to involve induction of the inositol (1,4,5)-trisphosphatediacylglycerol second messenger system, which mobilizes intracellular calcium and activates protein kinase C. In Experiment 1, endometrial explants taken from heifers on d 18.5 to 19.5 postestrus had increased PGF₂ secretion after treatment with 1 µM calcium ionophore A23187 to increase intracellular calcium, 100 nM phorbol 12-myristate 13-acetate to activate protein kinase C, and 100 nM oxytocin. The stimulatory effects of oxytocin and calcium ionophore A23187 plus phorbol 12-myristate 13-acetate did not differ from each other. In Experiment 2, endometrial explants taken from cows on d 18.5 to 19.5 postestrus had increased PGF₂ secretion after treatment with 0.2 and 2 µM thapsigargin to mobilize intracellular calcium that was sensitive to inositol (1,4,5)- trisphosphate. Secretion of PGF₂ was also increased by 100 nM oxytocin and was influenced by the interaction of thapsigargin and oxytocin such that 100 nM oxytocin did not further increase the secretion of PGF₂ in the presence of 2 µM thapsigargin. In Experiment 3, 100 nM oxytocin stimulated greater production of inositol trisphosphate and total inositol phosphates in the endometrium of cyclic cows than in the endometrium of pregnant cows on d 16.5 to 17.0 postestrus, although luteolysis was not yet initiated in the cyclic cows. These results are consistent with the hypothesis that the activation of the inositol (1,4,5)-trisphosphate-diacylglycerol second messenger system by oxytocin is involved in the stimulation of PGF₂ secretion from the endometrium during late diestrus in cows.

Key Words: endometrium • oxytocin • prostaglandin F₂ • inositol phosphate

Submitted on June 16, 1997
Accepted on September 19, 1997

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