Effect of oxytocin infusion on secretion of progesterone and luteinizing hormone and the concentration of uterine oxytocin receptors during the periovulatory period in cloprostenol-treated ewes

Abstract

= 5) infused animals.The oxytocin infusion maintained peripheral plasma concentrations of 53 \ m=+-\ 3\ m=. \ 2pg oxytocin ml \ m=-\ 1 (mean \ m=+-\ sem) compared with values of about 1 pg ml \ m=-\ 1 during oestrus in control ewes. Oxytocin infusion had no effect on luteal phase progesterone concentrations, the timing of luteolysis, basal luteinizing hormone (LH) secretion, LH pulse frequency, or the timing or height of the LH surge. Treated ewes came into oestrus significantly earlier than controls (P < 0\m=.\05) but ovulated normally. Uterine samples collected 96 h after cloprostenol injection (approximately day 2 of the cycle) showed that oxytocin receptor concentrations were significantly higher in the endometrium in ewes that had been given a 5 day oxytocin infusion than in control animals (556 and 262fmol mg\m=-\1protein, respectively: geometric means from ANOVA, P < 0\m=.\001), whereas myometrial receptor concentrations were not affected (113 and 162 fmol mg\m=-\1 protein, respectively).We conclude that the previously reported delay in luteal development caused by oxytocin infusion is not due to the inhibition or delay of ovulation, but must instead occur via a direct influence on the developing corpus luteum. Our results differ from those in rodents in which higher doses of oxytocin have been shown to influence both LH secretion and the timing of ovulation. Prolonged infusion with oxytocin at the dose used (the high end of the normal physiological range) during the periovulatory period does not cause downregulation of the oxytocin receptor.

The effect of oxytocin on the time of ovulation, conception, and embryonic survival in swine

“…(Wathes et al 1992). rather than with direct effects on the process of or.ulation as observed in the rat (Evans et al 1989;Robinson and Evans 1991).…”

Effect of oxytocin on in vitro prostaglandin production and expression of PGFS and PGES mRNAs in buffalo corpus luteum

“…Cows administered oxytocin on days 4 to 7 after inseminations are at a higher risk of pregnancy loss (Yildiz and Erisir 2006). In addition to the indirect effect of oxytocin on CL life cycle regulation via endometrial PGF 2 α secretion, delay in luteal development caused by oxytocin infusion occurs via a direct influence on the developing corpus luteum (Wathes et al 1992). There may be local interactions between oxytocin and PGF 2 α that play a role in the regulation of the CL (Bennegård-Edén et al 1995).…”

Effect of Intravenous Treatment with the Oxytocin Antagonist Atosiban on Circulating Progesterone in the Ewe

“…during mid-estrous cycle (Okuda et al, 1992). Oxytocin binding to luteal membranes and ovarian stroma was low throughout the estrous cycle in sheep (Wathes et al, 1992).…”