A NEURAL FACTOR IN THE MECHANISM BY WHICH ESTROGEN INDUCES THE RELEASE OF LUTEINIZING HORMONE IN THE RAT1

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Abstract
INTRODUCTION In polyestkous animals such as the rat, mouse, and guinea pig, which ovulate spontaneously, estrogen stimulates the release of luteinizing hormone from the hypophysis (Fevold, 1939; Hellbaum and Greep, 1946; Hisaw, 1947; Everett, 1947, and Bradbury, 1947). The liberated LH proceeds to induce preovulatory swelling, ovulation, formation of new corpora lutea and, in pregnant or pseudopregnant rats, cholesterinization of existing active corpora lutea (Everett, 1947). The spontaneously ovulating species do not require an overt neural stimulus, such as is presumably initiated by copulation, for the release of the gonadotrophic hormone. Nor is it established that coitus hastens ovulation in these animals. In this respect they differ from such species as the rabbit, cat and ferret, in which the release of an ovulating surge of LH normally occurs only after copulation. Conversely, estrogen alone will not stimulate discharge of LH in the animals of the latter type (Bachman, 1936; Dury and Bradbury, 1943).