AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 5 1241-R1250, Copyright © 1989 by American Physiological Society
Effect of ovariectomy and estradiol on unity of female rat circadian rhythms
E. M. Thomas and S. M. Armstrong
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Sixteen rats were ovariectomized and given either a 1-cm implant of
crystalline estradiol-17 beta (eight rats) or an empty implant (eight
rats). A further six rats were sham ovariectomized and given empty
implants, and eight rats were left unoperated. The rats were exposed to 70
days of constant dim light (LL) with a maximum illumination level of 20 lx,
and circadian running and drinking rhythms were monitored. In LL, both the
running and drinking activity rhythms of the ovariectomized,
blank-implanted rats became markedly disrupted, whereas unoperated and
sham-operated rats maintained unified rhythms. Estradiol-implanted rats
developed fewer rhythm desynchronies, and the majority displayed a single
band of free-running activity. Rather than being arrhythmic, the activity
of the LL-exposed ovariectomized rats appeared to contain several
free-running components. Thus these data are consistent with the concept of
a multioscillatory basis to the circadian system and support a role for the
ovary and its hormone estradiol in the maintenance of coherence between
component oscillators.
