A 24-HOUR PERIODICITY IN THE “LH-RELEASE APPARATUS” OF FEMALE RATS, DISCLOSED BY BARBITURATE SEDATION1

Abstract

UNTIL very recently the importance of the nervous system in evoking the ovulatory discharge of gonadotrophin has been recognized in only the few species of animals which fail to ovulate spontaneously. Within recent months, however, several reports from this laboratory (Sawyer, Everett and Markee, 1948, 1949; Everett, Sawyer and Markee, 1948, 1949; Everett and Sawyer, 1949, a, b; Sawyer, Markee and Everett, 1949, 1950) have demonstrated that in the rat, a spontaneous ovulator, neurogenic activation of the hypophysis is essential for the release of ovulating hormone. It was found that either Dibenamine or atropine, agents which block reflexogenic stimulation of the hypophysis in rabbits (Sawyer, Markee and Hollinshead, 1947; Sawyer, Markee and Townsend, 1949), will likewise prevent LH release in rats when injected before certain critical hours during proestrus. In our 4-day cyclic rats these hours are surprisingly uniform, usually between 2 and 4 p.m. Thus, atropine given at 2 p.m. or earlier uniformly prevents LH discharge.