AJP - Regulatory, Integrative and Comparative Physiology, Vol 243, Issue 1 70-R76, Copyright © 1982 by American Physiological Society
Increased heat loss in ovariectomized hypothyroid rats treated with estradiol
M. L. Laudenslager, H. J. Carlisle and S. E. Calvano
The role of the thyroid in the mediation of an estrogen-associated change
in thermal balance was studied in thyroidectomized and in
propylthiouracil-treated ovariectomized rats. Prior to propylthiouracil
treatment, estrogen-treated ovariectomized rats and intact female rats had
higher rates of heat production and dry heat loss at -5 degrees C than
ovariectomized rats. Heat production of estrogen-treated and intact female
rats was well below their rates of dry heat loss without an alteration in
the absolute rate of heat loss in the hypothyroid condition. Heat
production exceeded heat loss only in the hypothyroid ovariectomized group
not receiving estrogen. Ovariectomized rats without estrogen maintained
thermal balance, whereas rectal temperatures fell in both intact and
estrogen-treated ovariectomized rats during cold exposure. Increased heat
loss unbalanced by heat production was also observed in surgically
thyroidectomized estrogen-treated ovariectomized rats tested at -5 degrees
C. These results suggest that an estrogen-induced increase in heat loss,
which is compensated by an increase in heat production in the euthyroid but
not the hypothyroid condition, is one mechanism responsible for
estrogen-associated changes in thermal balance during cold exposure.
