title: Hormonal regulation of oxytocin-induced prostaglandin F(2alpha) secretion by the bovine and ovine uterus in vivo.
abstract: In long-term ovariectomized ewes and cows, endometrial oxytocin receptors rest at relatively high levels but oxytocin is unable to induce prostaglandin F(2alpha) 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 F(2alpha) 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.
authors.affiliation: University of Nottingham, School of Biosciences, Division of Animal Physiology, Sutton Bonington, LE12 5RD, Loughborough, UK. George.Mann@Nottingham.ac.uk
authors.forename: G E
authors.initials: GE
authors.lastname: Mann
authors.forename: J H
authors.initials: JH
authors.lastname: Payne
authors.forename: G E
authors.initials: GE
authors.lastname: Lamming
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism*; D004958:Estradiol / Q000097:blood / Q000494:pharmacology; D005260:Female; D006728:Hormones / Q000494:pharmacology*; D007700:Kinetics; D010052:Ovariectomy; D010121:Oxytocin / Q000494:pharmacology*; D011374:Progesterone / Q000097:blood / Q000494:pharmacology; D018045:Receptors, Oxytocin / Q000187:drug effects / Q000378:metabolism; D012756:Sheep / Q000502:physiology*; D014599:Uterus / Q000187:drug effects* / Q000378:metabolism
chemical_list: D006728:Hormones; D018045:Receptors, Oxytocin; C008228:15-keto-13,14-dihydroprostaglandin F2alpha; D011374:Progesterone; D004958:Estradiol; D010121:Oxytocin; D015237:Dinoprost