Prostaglandin F2 alpha and oxytocin release during persistence of the corpus luteum in sheep.

Abstract

Oxytocin (OT), progesterone and prostaglandin F2 alpha (PGF2 alpha) concentrations were measured in the utero-ovarian vein (UOV) of ewes which displayed persistence of the corpus luteum (CL). During the period of expected luteolysis, the frequency of OT and PGF2 alpha pulses in the UOV was significantly (P less than 0.005 for both) lower in ewes with persistent CLs, compared with ewes that underwent normal luteal regression. In contrast, the amplitude of both OT and PGF2 alpha pulses was similar in both groups of animals. It is suggested that persistence of the CL resulted from a decreased PGF2 alpha pulse frequency, which may have arisen from a decreased frequency of stimulation by OT. In two persistent CL ewes, however, it appeared that a failure at the level of the uterus may have contributed to the observed decrease in PGF2 alpha release. Although a PGF2 alpha analogue (Lutalyse) infusion into the uterine vein of two ewes with persistent CLs failed to induced luteolysis, it did stimulate a large release of OT into the UOV. This suggests that persistent CLs maybe more resistant to PGF2 alpha and, that at day 22 post-oestrus, these CLs are capable of releasing large quantities of OT into the UOV.