Oxytocin delays oestradiol-induced luteolysis but does not affect oestradiol-induced luteinizing hormone secretion in the ewe.
Circulating concentrations of progesterone, the prostaglandin F2 alpha (PGF2 alpha), metabolite 13,14-dihydro-15-keto PGF2 alpha (DHKF2 alpha) and luteinizing hormone (LH) have been measured in cyclic ewes receiving a continuous infusion of oxytocin, in order to investigate the effect of maintained concentrations of circulating oxytocin on the luteolytic action of oestradiol-17 beta. Oxytocin (3 nmol h-1 intravenously) was given from Day 7 until Day 17 after oestrus with oestradiol-17 beta (2.76 mumol, intramuscularly in sesame oil, 0.5 mL-1) administered on Days 9 and 10. Control ewes, given a continuous infusion of saline (154 mmol L-1, 3 mL-1 h-1) and sesame oil on Days 9 and 10, underwent luteal regression at the expected time, with mean concentrations of plasma progesterone falling to below 1.5 nmol L-1 on Day 16 (0900 hours). Mean plasma progesterone concentrations fell to less than 1.5 nmol L-1 on Day 13 (0900 hours) in ewes receiving saline and oestradiol-17 beta. Oxytocin infusion delayed luteolysis in all treated ewes; those receiving oxytocin infusion and sesame oil failed to undergo luteal regression during the period studied and in animals receiving oxytocin and oestradiol-17 beta, luteolysis was significantly delayed when compared to ewes treated with saline and oestradiol with progesterone concentrations falling to < 1.5 nmol L-1 on Days 14 (n = 1 ewe), 15 (n = 1 ewe), 16 (n = 2 ewes) and > 17 (n = 2 ewes) (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Sheldrick
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AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, England.
D000818:Animals; D003338:Corpus Luteum / Q000187:drug effects* / Q000378:metabolism; D015237:Dinoprost / Q000031:analogs & derivatives / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007262:Infusions, Intravenous / Q000662:veterinary; D008183:Luteal Phase / Q000187:drug effects; D007986:Luteinizing Hormone / Q000378:metabolism*; D010121:Oxytocin / Q000008:administration & dosage / Q000494:pharmacology*; D011374:Progesterone / Q000097:blood; D012756:Sheep / Q000502:physiology*
C008228:15-keto-13,14-dihydroprostaglandin F2alpha; D011374:Progesterone; D004958:Estradiol; D010121:Oxytocin; D007986:Luteinizing Hormone; D015237:Dinoprost