Role of the oxytocin receptor in the choice between cyclicity and gestation in ruminants.

The endometrial oxytocin receptor occupies a central point in the choice between luteolysis and pregnancy in ruminants. Receptor expression determines the time at which luteolysis occurs in nonpregnant animals, and thereby determines the duration of the oestrous cycle. Inhibition of receptor expression by trophoblast interferon (IFN) blocks the process of luteal regression and leads to continued progesterone secretion and the successful growth of the conceptus. Trophoblast IFN is probably required from the time of normal luteolysis during the cycle until luteal oxytocin concentrations of pregnancy decline, thus removing the stimulatory mechanism for the release of the episodes of prostaglandin F2 alpha required for luteolysis.