Influence of oxytocin infusion during oestrus and the early luteal phase on progesterone secretion and the establishment of pregnancy in ewes.

Department of Anatomy, School of Medical Sciences, Bristol, UK.
J Reprod Fertil 08/1991; 92(2):383-91. DOI: 10.1530/jrf.0.0920383
Source: PubMed

ABSTRACT In Experiment 1, an osmotic minipump containing oxytocin was implanted s.c. in ewes for 12 days beginning on Day 10 of the oestrous cycle, producing approximately 100 pg oxytocin/ml in the plasma. Two days after the start of infusion, all ewes were injected with 100 micrograms cloprostenol and placed with a fertile ram. At slaughter 22 days later, 9 (75%) of the 12 control (saline-infused) ewes were pregnant compared with 1 (11%) of the 9 ewes infused with oxytocin. In the control group, midcycle plasma concentrations of oxytocin were significantly higher in nonpregnant than in pregnant ewes. In Experiment 2, an infertile ram was used throughout to avoid any possible effects of pregnancy and oxytocin infusions were given at different stages of the oestrous cycle. Otherwise the protocol was similar to that in Exp. 1. Oxytocin infusion during luteolysis and the early follicular phase had no effect on the subsequent progesterone secretion pattern, but infusions beginning the day before cloprostenol-induced luteolysis and lasting for 7 or 12 days and infusions beginning on the day of oestrus for 4 days all delayed the subsequent rise in plasma progesterone by approximately 3-4 days. In these animals, the cycle tended to be longer. It was concluded that an appropriate oxytocin secretion pattern may be necessary for the establishment of pregnancy in ewes and that a high circulating oxytocin concentration during the early luteal phase delays the development of the young corpus luteum.

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    ABSTRACT: Twenty-five normally cyclic Holstein heifers were used to examine the effects of oxytocin on cloprostenol-induced luteolysis, subsequent ovulation, and early luteal and follicular development. The heifers were randomly assigned to 1 of 4 treatments: Group SC-SC (n=6), Group SC-OT (n=6), Group OT-SC (n=6) and Group OT-OT (n=7). The SC-SC and SC-OT groups received continuous saline infusion, while Groups OT-SC and OT-OT received continuous oxytocin infusion (1:9 mg/d) on Days 14 to 26 after estrus. All animals received 500 microg, i.m. cloprostenol 2 d after initiation of infusion (Day 16) to induce luteolysis. Groups SC-OT and OT-OT received oxytocin twice daily (12 h apart) (0.33 USP units/kg body weight, s.c.) on Days 3 to 6 of the estrous cycle following cloprostenol-induced luteolysis, while Groups SC-SC and OT-SC received an equivalent volume of saline. Daily plasma progesterone (P4) concentrations prior to cloprostenol-induced luteolysis and rates of decline in P4 following the induced luteolysis did not differ between oxytocin-infused (OT-OT and OT-SC) and saline-infused (SC-SC and SC-OT) groups (P >0.1). Duration of the estrous cycle was shortened in saline-infused heifers receiving oxytocin daily during the first week of the estrous cycle. In contrast, oxytocin injections did not result in premature inhibition of luteal function and return to estrus in heifers that received oxytocin infusion (OT-OT). Day of ovulation, size of ovulating follicle and time of peak LH after cloprostenol administration for oxytocin and saline-treated control heifers did not differ (P >0.1). During the first 3 d of the estrous cycle following luteal regression, fewer (P <0.01) follicles of all classes were observed in the oxytocin-infused animals. Day of emergence of the first follicular wave in heifers treated with oxytocin was delayed (P <0.05). The results show that continuous infusion of oxytocin during the mid-luteal stage of the estrous cycle has no effect on cloprostenol-induced luteal regression, timing of preovulatory LH peak or ovulation. Further, the finding support that an episodic rather than continuous administration of oxytocin during the first week of the estrous cycle results in premature loss of luteal function. The data suggest minor inhibitory effects of oxytocin on follicular growth during the first 3 d of the estrous cycle following cloprostenol-induced luteolysis.
    Theriogenology 04/2000; 53(4):963-79. · 2.08 Impact Factor
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    ABSTRACT: Embryonic survival after administration of oxytocin (OT) was examined in 42 beef cows. All cows were bred (Day 0) and randomly assigned to receive either 25 mL saline (CON; n = 10), 100 IU OT + 20 mL saline (OT; n = 12), 100 IU OT + 1 g flunixin meglumine (OT + FM; inhibitor of prostaglandin endoperoxide synthase; n = 10), or 100 IU OT + lutectomy (OT + LUT; n = 10) administered (i.m.) at 8-h intervals on Days 5-8 after mating. Lutectomies were performed by transrectal digital pressure prior to initiation of treatments (0600, Day 5). All cows were fed 4 mg/head/day of melengesterol acetate (an orally administered exogenous progestogen) through Days 3-30 and were bled by jugular venipuncture at 0600 and 0700 h on Day 5 for determination of 13,14-dihydro-15-keto-PGF2a (PGFM). Pregnancy rates, as determined by transrectal ultrasonography at Day 30, were reduced in OT (33.3%) and OT + LUT (30%) groups compared to CON and OT + FM (80%; p < or = 0.03). Number of short cycles were increased in OT (n = 6/12) group compared to CON (n = 0/10; p < or = 0.009) and OT + FM (n = 1/10; p < or = 0.045). Mean change in PGFM from the 0600 to 0700 h bleed was different (p < or = 0.01) between the OT + LUT (31.6 +/- 11.0 pg/mL) group versus CON (-11.2 +/- 10.6 pg/mL) and OT + FM (-13.8 +/- 10.6 pg/mL) groups. Administration of oxytocin appears to decrease embryonic survival by stimulating uterine PGF2a. Thus, previous reports indicating that removal of the corpus luteum during progestogen supplementation and prior to PGF2a administration increases embryonic survival can be explained through interruption of the luteal oxytocin-uterine PGF2a feedback loop.
    Prostaglandins & other lipid mediators 07/1999; 57(4):259-68. · 2.42 Impact Factor
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    ABSTRACT: Yildiz A., Z. Erisir : Effects of Exogenous Oxytocin on Embryonic Survival in Cows. Acta Vet Brno 2006, 75: 73-78. The aim of this study was to evaluate the effect of oxytocin on embryonic survival in dairy cows. Pregnancy was verified using the early pregnancy factor (EPF) activity on Day 4 after artificial insemination (AI). Pregnant cows were randomly allotted to two groups: treated (n = 8) and control (n = 8). Oxytocin (100 IU, 5 ml, DIF Turkey) was administered twice daily by intravenous injections to treated cows and sterile saline (5 ml) to control cows immediately before milking on days 4 to 7 after AI. Blood samples were taken via jugular vein every day from day 4 to 8 and every other day until Day 20 following insemination to evaluate the effect of oxytocin on embryonic survival. The embryonic loss was diagnosed in 3 of the 8 cows treated with oxytocin, and embryonic survival rate was 62.5% in this group versus 87.5% in controls. Short cycles occurred in 37.5% of oxytocin-treated cows. At the same time their serum progesterone concentrations rose more slowly than in controls. It was concluded that cows administered oxytocin on days 4 to 7 after insemination are at a higher risk of pregnancy loss.
    Acta Veterinaria Brno - ACTA VET BRNO. 01/2006; 75(1):73-78.

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