title: Influence of estradiol and progesterone withdrawal on the secretion of and the temporal correlation between pulses of oxytocin and prostaglandin F2(alpha) in ewes.
abstract: The primary objective was to examine the effects of estradiol and the progesterone receptor antagonist onapristone on the pulsatile secretion of prostaglandin F(2alpha) (PGF(2alpha)) and ovarian and pituitary oxytocin. A 2 x 2 factorial arrangement of estradiol and onapristone treatments was administered to groups of 5 ewes after destruction of ovarian follicles on Day 8 of the cycle. Estradiol treatments consisted of the administration of a silicone elastomer implant, either containing or not containing estradiol, on Day 8 plus 50 microg of estradiol or corn oil on Days 11 and 12. Onapristone (2 mg/kg) or its vehicle were administered on Day 13, immediately preceding the simultaneous collection of blood samples from the carotid artery, jugular vein, and vena cava at 7.5-min intervals for 7 h. Ewes were immediately killed for measurements of uterine oxytocin receptor concentrations and phosphatidylinositide turnover. More oxytocin pulses were detected in the jugular vein than in the carotid artery (p < 0.01), suggesting that the pituitary is a source of oxytocin. A similar number (p > 0.1) of PGF(2alpha) pulses were correlated with oxytocin pulses as were not. The linked PGF(2alpha) pulses were longer in duration (p = 0.01) with a tendency toward a higher amplitude (p = 0.08). The corresponding vena caval oxytocin pulses had a longer duration (p = 0.02) than those not linked to PGF(2alpha). Estradiol increased oxytocin receptor concentrations and the turnover of phosphatidylinositides (p = 0.02) without affecting PGF(2alpha) pulse characteristics. Onapristone increased (p = 0.03) PGF(2alpha) pulse amplitude. Although a lower than expected temporal correlation between oxytocin and PGF(2alpha) pulses was observed, the distinguishing characteristics of linked pulses may be indicative of their physiological significance.
authors.affiliation: Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana 61081, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Walker
authors.forename: P G
authors.initials: PG
authors.lastname: Weston
authors.forename: J E
authors.initials: JE
authors.lastname: Hixon
mesh_terms: D000818:Animals; D015237:Dinoprost / Q000378:metabolism*; D004958:Estradiol / Q000008:administration & dosage / Q000378:metabolism*; D005260:Female; D006067:Gonanes / Q000008:administration & dosage; D006727:Hormone Antagonists / Q000008:administration & dosage; D003341:Luteolysis / Q000187:drug effects / Q000502:physiology; D010121:Oxytocin / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism*; D018045:Receptors, Oxytocin / Q000378:metabolism; D011980:Receptors, Progesterone / Q000037:antagonists & inhibitors; D012756:Sheep; D013997:Time Factors; D014599:Uterus / Q000187:drug effects / Q000378:metabolism
chemical_list: D006067:Gonanes; D006727:Hormone Antagonists; D010716:Phosphatidylinositols; D018045:Receptors, Oxytocin; D011980:Receptors, Progesterone; D011374:Progesterone; D004958:Estradiol; D010121:Oxytocin; D015237:Dinoprost; C053238:onapristone