THE TIME OF RELEASE OF OVULATING HORMONE FROM THE RAT HYPOPHYSIS1

Abstract

THE rabbit hypophysis needs about one hour to release enough gonadotrophin to cause ovulation, a fact that has been known for over 25 years (7). The information was accessible because of the well-recognized “reflex” character of ovulation in that species. The recent demonstration in rats of a neurogenous stimulus to the hypophysis with a predictable relationship to time of day (4, 6), makes it feasible in this spontaneously ovulating form to ask at what relative time of day the release of hormone occurs and how long the process lasts. By the use of various drugs that will block the reflex stimulation of the rabbit hypophysis (notably Dibenamine, atropine and Nembutal), administered to cycling female rats at different times of the day of proestrus, one can delimit a “critical period” before which the treatment will regularly prevent ovulation and after which most animals will ovulate in spite of the treatment (4, 6).