Kl. Ryan et al., ARTERIAL BAROREFLEX MODULATION OF HEAT-INDUCED VASODILATION IN THE RABBIT EAR, Journal of applied physiology, 83(6), 1997, pp. 2091-2097
The purpose of this study was to determine whether nonthermal barorefl
exes arising from cardiopulmonary and/or arterial baroreceptors modula
te rabbit ear blood flow (EBF) during hyperthermia. Intact and sinoaor
tic-denervated (SAD) rabbits were chronically instrumented with a Dopp
ler ultrasonic flow probe for measurement of EBF velocity (kHz). Durin
g whole body heating in conscious rabbits, EBF and ear vascular conduc
tance (EVC) increased as core temperature increased until maximal plat
eau levels of EBF and EVC were reached. The maximal plateau level of E
VC attained during heat stress was lower in SAD than in intact rabbits
. Subsequent intrapericardial administration of procaine at maximal EB
F blocked cardiac afferents but did not alter EVC in either animal gro
up. In a second experiment, ramp decreases in mean arterial pressure w
ere produced by vena caval occlusion at maximal EBF. In intact rabbits
, EBF and EVC decreased linearly as mean arterial pressure fell, but E
BF and EVC did not decrease during vena caval occlusion in SAD rabbits
. Thus neither pharmacological nor mechanical unloading of cardiac bar
oreceptors results in reflex vasoconstriction in the heat-stressed rab
bit ear. However, baroreflexes arising from arterial baroreceptors may
modulate EBF in heat-stressed rabbits.