A NEUROGENIC TIMING FACTOR IN CONTROL OF THE OVULATORY DISCHARGE OF LUTEINIZING HORMONE IN THE CYCLIC RAT1

Abstract

INTRODUCTION It was reported in the preceding paper (Sawyer, Everett and Markee, 1949) that a neural factor is involved in the release of LH from the female rat hypophysis in response to estrogen treatment, thus extending to a “spontaneously” ovulating species principles whichhad been previously disclosed in the rabbit (Markee, et al., 1946, 1948; Sawyer, et al., 1947, 1948). Although estradiol benzoate injected on the fourth day of pregnancy in the rat regularly induces ovulation within 48 hours (Everett, 1947), this effect could be prevented in most cases by Dibenamine or atropine, administered as late as 20 hours after the estrogen. It was proposed that estrogen modifies the threshold of activation ofan hypothalamic center, or of certain afferentpathways leading to the “center,” and that a chief difference between the rabbit and rat lies in the particular afferent pathways concerned.