Journal of Applied Physiology, Vol 49, Issue 3 363-366, Copyright © 1980 by American Physiological Society
Effects of apomorphine and pimozide on temperature regulation during exercise in the rat
C. V. Gisolfi, F. Mora, S. Bloomfield, M. Beattie and S. Magnes
The purpose of this study was to determine the effects of a specific
dopamine receptor agonist (apomorphine) and antagonist (pimozide) on
thermoregulation when the heat loss pathway was activated by the stress of
exercise. Apomorphine or its control vehicle (0.9% wt/vol saline) was
injected systemically (0.5, 1.0, 1.5 mg/kg ip) or within the
preoptic-anterior hypothalamus (5, 10, 20 micrograms) immediately before
the start of treadmill exercise at 21.5 m/min. Colonic, tailskin, and
ambient temperatures were recorded each minute. Oxygen consumption was
calculated from on-line measurements of percent O2 and CO2. Pimozide
injected systemically (0.5 mg/kg ip) had no effect on resting colonic
temperature, but caused a significant (P less than 0.05) hyperthermia
during treadmill exercise compared to saline controls. Central and systemic
injections of apomorphine caused a dose-dependent hypothermia that was
blocked by pretreatment with pimozide. Oxygen uptake values during exercise
following the central injection of apomorphine were virtually identical to
those following the injection of saline, but colonic temperature was
significantly (P less than 0.05) lower than saline controls, indicating
that the hypothermia observed was not due to a reduction in metabolic rate.
These data indicate that dopamine receptors in the preoptic-anterior
hypothalamus of the rat participate in the mediation of heat dissipation
when the animal is challenged with a heat stress.
