Hormonal regulation of oxytocin-induced prostaglandin F2alpha secretion by the bovine and ovine uterus in vivo
2001
Mann, G.E. | Payne, J.H. | Lamming, G.E.
In long-term ovariectomized ewes and cows, endometrial oxytocin receptors rest at relatively high levels but oxytocin is unable to induce prostaglandin F2alpha release. A series of studies were carried out to investigate the roles of physiological levels of progesterone and estradiol in "activating" these receptors in terms of permitting oxytocin-induced prostaglandin F2alpha release. In long-term ovariectomized cows, treatment with progesterone, but not estradiol, resulted in the induction of responsiveness to oxytocin. This responsiveness appeared within 2 d of progesterone treatment, reached a maximum by 6 d and was maintained to Day 18. In ovariectomized ewes, while estradiol treatment did induce temporary responsiveness to oxytocin after 3 d of treatment, treatment with progesterone was required to induce sustained responsiveness that appeared by Day 9 of treatment and was maintained to Day 12. Measurement of endometrial receptors for oxytocin revealed a significant decline in oxytocin receptors by Day 6 of progesterone treatment when responsiveness to oxytocin was maximal, demonstrating that receptor concentrations were not a limiting factor. The most likely mechanism by which progesterone treatment induces responsiveness to oxytocin may be through the up regulation of post receptor signaling pathways and/or enzymes involved in prostaglandin synthesis.
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