AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 3 673-R677, Copyright © 1994 by American Physiological Society
Effects of estrogen on thermoregulatory evaporation in rats exposed to heat
M. A. Baker, D. D. Dawson, C. E. Peters and A. M. Walker
Division of Biomedical Sciences, University of California, Riverside 92521.
The purpose of this study was to determine the effects of estrogen (E2)
replacement on thermoregulation in ovariectomized rats exposed to heat.
Female Sprague-Dawley rats were ovariectomized and splenectomized and
implanted with a temperature-sensitive transmitter. Each rat was studied
when E2 treated (after an E2 pellet implant) and untreated. Animals were
divided into two groups with opposite order of treatment and were studied
over a 9-wk period. Measurements of body core temperature (Tc) and
evaporative water loss (EWL) were made on unrestrained animals resting at
38 degrees C air temperature. E2-treated animals increased EWL at all
levels of Tc, reduced the threshold Tc for onset of saliva spreading, and
regulated Tc at a lower level during heat exposure. E2 treatment elevated
plasma E2 and reduced hematocrit but did not affect plasma osmolality.
These effects of E2 on evaporative cooling and Tc in heat-stressed rats are
similar to those that have been reported in human females. The mechanisms
of the thermoregulatory effects of E2 remain to be studied.
