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Departments of 1 Exercise Science and 2 Pharmacology, The University of Iowa, Iowa City, Iowa 52242
During hyperthermia, vasoconstrictor tone
in the viscera is lost despite high levels of sympathetic neural
outflow and plasma catecholamines, suggesting that vascular
responsiveness to adrenergic receptor stimulation is reduced. The
purpose of this study was to determine whether adrenoceptor-mediated
control of vascular resistance is altered at high body core
temperatures. The hemodynamic responses to adrenoceptor agonists were
examined in chloralose-anesthetized rats heated to colonic temperatures
(Tco) of 37, 39, and 41.5°C. Elevating Tco to 39°C did not
alter the hemodynamic responses to any of these agents. Further heating
to 41.5°C markedly attenuated the hemodynamic responses to
- and
-adrenoceptor agonists. Similarly, the regional and systemic
hemodynamic responses to ANG II and endothelin were also reduced at
41.5°C. In contrast, the hemodynamic responses to
endothelium-dependent and -independent vasodilator agents were
unchanged or slightly reduced at 41.5°C. The blunted hemodynamic
responses observed at 41.5°C indicate that vascular reactivity to
vasoconstrictor agents is reduced with hyperthermia and suggest that
this nonspecific change in vascular responsiveness may contribute the
circulatory collapse associated with high body temperatures.
adrenoceptor agonists; vasodilator agents; hyperthermia; regional vascular resistance; vascular responsiveness
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