Timing of the Estrogen-Induced Release of LH in Ovariectomized Rats Under an Altered Lighting Schedule 1

Abstract

Summary

Previous results from this laboratory (4) have shown that rats submitted to a 0500-1900 hr “lights-on” schedule responded to a single estradiol administration 48 hr after ovariectomy with plasma LH rises only during the afternoon (1630-1700 hr) of the following days. Under otherwise similar experimental conditions, it is now reported that if the “lights-on” period is shifted to 2100-1100 hr, the estrogen-induced LH surges occur at 1100-1230 hr. Cycling rats submitted to the altered illumination schedule show similarly altered times of the proestrous surge. The results reveal that the estrogen-induced LH rise in ovarieetomized animals is synchronized by light, and suggest that similar mechanisms control this estrogen-induced LH surge in ovariectomized rats and the spontaneous proestrous LH surge in cycling rats.

We thank Ms. Francis Smith and Kathy Bangs and Mr. David Whitmoyer for valuable technical assistance and Mr. Bob McAlister for drawing the figures.