Timing the Preovulatory Surge of Gonadotropin Secretion

Abstract

Boling et al. (1941) correlated ovulation time in rats with the interval from the beginning of heat behavior. Inasmuch as the beginning of heat in these rodents is itself related to the time of day (Hemmingsen and Krarup 1937), it follows that ovulation is governed in some manner by events related to circadian periodicity. It is now common knowledge that a major determinant is a pronounced surge of LH secretion on the afternoon of proestrus, beginning during a so-called “critical period” of a few hours, cued in turn by the photoperiod to which the animal is exposed. Awareness of the close relationship of ovulation time to clock hours in rats came from the studies with progesterone and estrogen outlined in the previous section.