AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 4 915-R923, Copyright © 1992 by American Physiological Society
Potentiation of thermoregulatory responses to isoproterenol by beta-adrenergic antagonists
H. J. Carlisle and M. J. Stock
Department of Psychology, University of California, Santa Barbara 93106.
The thermoregulatory effects of isothermogenic doses of isoproterenol (Iso)
and a novel beta-agonist (BRL 35135) were tested in rats at 22 degrees C
and in rats trained to bar press for radiant heat at -8 degrees C. BRL
35135 produced hyperthermia at 22 degrees C and reduced operant responding
for heat at -8 degrees C, whereas Iso reduced body temperature and
increased operant responding. In both situations, the negative effects of
Iso on thermal balance were abolished by propranolol at doses that did not
inhibit heat production. In anesthetized rats, propranolol potentiated the
Iso-induced rise in brown adipose tissue and colonic temperature. The
potentiation was more marked with the beta 2-selective antagonist ICI
118,551, whereas treatment with the beta 1-selective antagonist atenolol
resulted in a profound Iso-induced reduction in temperature. The two
selective antagonists also produced divergent responses in operant behavior
in Iso-treated rats at -8 degrees C. These experiments demonstrate the
extent to which responses to a nonselective agonist can be manipulated
using appropriately low doses of selective antagonists and indicate that
the effects of Iso on thermal balance are due to its beta 2 activity.
