A NEURAL TIMING FACTOR IN THE MECHANISM BY WHICH PROGESTERONE ADVANCES OVULATION IN THE CYCLIC RAT

Abstract

INTRODUCTION Under certain conditions progesterone will advance ovulation in cyclic rats about 24 hours (Everett, 1944a, 1948). This result occurs, not in 4-day cycles, but very regularly in 5-day cycles when progesterone is administered about noon on the third day of diestrus. Various reasons were presented (1948) for concluding that this effect is brought about indirectly through the hypophysis by inducing the release of luteinizing hormone (or total gonadotrophin). Independent observations have been made by Fraps and Dury (1943) that in the domestic hen progesterone administration will advance ovulation several hours. More recent evidence (Rothchild and Fraps, 1949) shows that this process, like that in rats, requires the presence of the hypophysis. Their findings indicate, furthermore, that a direct time relationship exists between the hour of progesterone injection and the hour of response, release of the “ovulating hormone” occurring about 4 hours after the injection of progesterone.