Delayed luteal regression in ewes immunized against oxytocin

Abstract

Active immunization of sheep against oxytocin prolonged the luteal phase of the estrous cycle, as judged by estrous behavior and circulating progesterone concentrations. Mean cycle length was extended by 3.7 days. The treatment resulted in a 10-fold increase in circulating oxytocin concentrations. Antisera produced were specific for oxytocin; cross-reactions with vasotocin, arginine vasopressin and hypothalamic releasing factors were low. CSF contained low levels of antibodies directed against oxytocin. The luteolytic action of estradiol-17.beta. in sheep may be mediated through a stimulatory effect on the endometrial oxytocin receptor concentration.