title: Oxytocin-induced secretion of prostaglandin F2alpha in postpartum beef cows: effects of progesterone and estradiol-17beta treatment.
abstract: The purpose of the present study was to determine the effect of progesterone or progesterone + estradiol-17beta on oxytocin-induced prostaglandin F2alpha (PGF2alpha) secretion in postpartum beef cows. Thirty-four anestrous postpartum beef cows were ovariectomized (d 32 [Groups 1 to 3] or d 23 [Groups 4 to 6] postpartum [d 0 = parturition]) and allotted to six treatments (Group 1; negative control) to simulate short (Groups 2 through 5) or normal (Group 6) length estrous cycles. Steroid treatments for the respective groups were as follows: Group 1) no estradiol-17beta or progesterone treatment (n = 8; negative control); Group 2) progesterone (d 34 to 40; n = 6); Group 3) estradiol-17beta (d 32 to 33) and progesterone (d 34 to 40; n = 6); Group 4) progesterone (d 23 to 29), no estradiol-17beta (d 32 to 33), and progesterone (d 34 to 40; n = 5); Group 5) progesterone (d 23 to 29), estradiol-17beta (d 32 to 33), and progesterone (d 34 to 40; n = 5); and Group 6) progesterone (d 23 to 29), estradiol-17beta (d 32 to 33), and progesterone (d 34 to 50; n = 4; positive control). Oxytocin (100 IU) was injected (i.v.) at the end of each treatment to test the ability of the postpartum uterus to secrete PGF2alpha as measured by a stable metabolite of PGF2alpha, 15keto-13,14 dihydro-PGF2alpha (PGFM). Peak concentrations ofPGFM (P < 0.08) and total PGFM secreted (area under the curve; P < 0.05) were increased on d 6 following first (Group 2) or second (Group 4) exposure to progesterone and were similar to peak concentrations and total PGFM secreted 16 d following a simulated normal estrous cycle (Group 6). Administration of estradiol-17beta before first progesterone exposure (Group 3) did not reduce peak concentrations of PGFM or total PGFM secreted relative to the preceding groups. Peak concentrations of PGFM (P < 0.08) and total PGFM secreted (P < 0.05) were reduced following a second progesterone exposure, provided that cows were pretreated with estradiol-17beta (Group 5). In summary, oxytocin-induced release of PGFM was inhibited on d 6 following second exposure to progesterone only when cows were pretreated with estradiol-17beta. Therefore, estradiol-17beta and progesterone were both associated with the timing of PGF2, secretion in postpartum cows.
authors.affiliation: Animal Sciences Department, University of Missouri, Columbia 65211, USA.
authors.forename: K R
authors.initials: KR
authors.lastname: Kieborz-Loos
authors.forename: H A
authors.initials: HA
authors.lastname: Garverick
authors.forename: D H
authors.initials: DH
authors.lastname: Keisler
authors.forename: S A
authors.initials: SA
authors.lastname: Hamilton
authors.forename: B E
authors.initials: BE
authors.lastname: Salfen
authors.forename: R S
authors.initials: RS
authors.lastname: Youngquist
authors.forename: M F
authors.initials: MF
authors.lastname: Smith
mesh_terms: D000818:Animals; D002417:Cattle / Q000378:metabolism* / Q000502:physiology; D015237:Dinoprost / Q000378:metabolism*; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D008183:Luteal Phase; D010052:Ovariectomy / Q000662:veterinary; D010121:Oxytocin / Q000494:pharmacology*; D049590:Postpartum Period / Q000378:metabolism; D011247:Pregnancy; D011374:Progesterone / Q000494:pharmacology*; D011897:Random Allocation
chemical_list: D011374:Progesterone; D004958:Estradiol; D010121:Oxytocin; D015237:Dinoprost