title: Oxytocin induction of pulses of a prostaglandin metabolite and luteolysis in mares.
abstract: A procedure for oxytocin (OT) administration on Day 13 postovulation was developed in mares for stimulation of a pulse of PGFM (a PGF2α metabolite) that mimics a natural PGFM pulse during luteolysis. Bolus treatment with each of five OT doses (1-10 IU/mare, n = 3) stimulated a burst of PGFM that was maximum in 4 minutes and was unlike a natural pulse. A 2-hour OT infusion of 1.25, 2.5, or 5 IU/100 kg (n = 4) induced a PGFM pulse similar to reported pulses; lower doses did not. The peak of an induced pulse (approximately 260-380 pg/mL) seemed similar to reported natural peaks (approximately 200-300 pg/mL), using the same assay system. The interval from nadir to nadir was 6.6 ± 0.2 hours. Percentage decrease in progesterone (P4) within 8 hours was greater (P < 0.05) for doses of 1.25, 2.5, or 5 IU/100 kg (43%-50%) than that for a vehicle group (11%). Treatment with flunixin meglumine (1.0 mg/kg), a cyclooxygenase inhibitor, decreased (P < 0.008) P4 concentration, but treatment 2 hours before the beginning of OT infusion (2.5 IU/100 kg) did not prevent the OT-induced PGFM pulses and the decrease in P4. In conclusion, a PGFM pulse was simulated by infusion of OT during 2 hours but not by a single OT bolus, and an OT-simulated PGFM pulse stimulated a decrease in P4 that was not prevented by a cyclooxygenase inhibitor. These are the first firm demonstrations that OT in mares as in other species has a role in luteolysis.
authors.affiliation: Eutheria Foundation, Cross Plains, Wisconsin, USA; Departamento de Medicina Veterinária, Escola de Ciências e Tecnologia, Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Instituto de Investigação e Formação Avançada, Universidade de Évora, Évora, Portugal; Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA.
authors.forename: V G
authors.initials: VG
authors.lastname: Santos
authors.affiliation: Eutheria Foundation, Cross Plains, Wisconsin, USA; Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA.
authors.forename: T
authors.initials: T
authors.lastname: Castro
authors.affiliation: Departamento de Medicina Veterinária, Escola de Ciências e Tecnologia, Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Instituto de Investigação e Formação Avançada, Universidade de Évora, Évora, Portugal.
authors.forename: E M
authors.initials: EM
authors.lastname: Bettencourt
authors.affiliation: Eutheria Foundation, Cross Plains, Wisconsin, USA; Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA. Electronic address: ginther@vetmed.wisc.edu.
authors.forename: O J
authors.initials: OJ
authors.lastname: Ginther
mesh_terms: D000818:Animals; D015237:Dinoprost / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism; D006736:Horses / Q000502:physiology*; D003341:Luteolysis / Q000187:drug effects / Q000502:physiology*; D010060:Ovulation / Q000187:drug effects*; D010121:Oxytocin / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: C008228:15-keto-13,14-dihydroprostaglandin F2alpha; D010121:Oxytocin; D015237:Dinoprost
keywords: Luteolysis; Mares; Oxytocin; PGFM; Progesterone