Key result
In heat-stressed rabbits, neither pharmacological nor mechanical unloading of cardiac baroreceptors resulted in reflex vasoconstriction in the ear, though arterial baroreflexes may modulate ear blood flow.
Baroreflexes arising from arterial baroreceptors, but not cardiac baroreceptors, may modulate ear blood flow in heat-stressed rabbits.
Animal findings do not support cardiac baroreflex control of ear vasoconstriction; leaves open arterial baroreflex role in human thermoregulation.
The purpose of this study was to determine whether nonthermal baroreflexes arising from cardiopulmonary and/or arterial baroreceptors modulate rabbit ear blood flow (EBF) during hyperthermia. Intact and sinoaortic-denervated (SAD) rabbits were chronically instrumented with a Doppler ultrasonic flow probe for measurement of EBF velocity (kHz). During whole body heating in conscious rabbits, EBF and ear vascular conductance (EVC) increased as core temperature increased until maximal plateau levels of EBF and EVC were reached. The maximal plateau level of EVC attained during heat stress was lower in SAD than in intact rabbits. Subsequent intrapericardial administration of procaine at maximal EBF blocked cardiac afferents but did not alter EVC in either animal group. In a second experiment, ramp decreases in mean arterial pressure were produced by vena caval occlusion at maximal EBF. In intact rabbits, EBF and EVC decreased linearly as mean arterial pressure fell, but EBF and EVC did not decrease during vena caval occlusion in SAD rabbits. Thus neither pharmacological nor mechanical unloading of cardiac baroreceptors results in reflex vasoconstriction in the heat-stressed rabbit ear. However, baroreflexes arising from arterial baroreceptors may modulate EBF in heat-stressed rabbits.
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Ryan et al. (1997) studied this question. Sinoaortic denervation (SAD) and baroreceptor unloading vs. Intact rabbits was evaluated on Ear blood flow (EBF) and ear vascular conductance (EVC). In heat-stressed rabbits, neither pharmacological nor mechanical unloading of cardiac baroreceptors resulted in reflex vasoconstriction in the ear, though arterial baroreflexes may modulate ear blood flow.
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