Abstract
In reptiles, rates of heat transfer between the animal and its environment are controlled by the regulation of blood flow in the body. A faster heart rate during heating compared to cooling is thought to facilitate heat transfer, allowing reptiles to attain a higher body temperature more rapidly. Changes in cardiac output are complemented by changes in the resistance of vascular beds and a redistribution of blood flow between the core and periphery during heating and cooling. Cardiovascular regulation during thermoregulation is under the control of the autonomic nervous system and by local vasoactive substances released in the peripheral vasculature in response to heat. In a recent study we tested the hypothesis that regional differences in blood flow during heating and cooling occur independently from changes in heart rate. We measured heart rate, blood pressure, and surface flow by Laser Doppler flowmetry, and used coloured microspheres to track blood flow patterns to different parts of the body of the estuarine crocodile during heating and cooling with and without a blockade of cholinergic and β-adrenergic receptors. Heart rates during heating were significantly faster than during cooling in the control, but not when autonomic receptors were blocked. There were no differences in blood flow distribution between control and autonomic blockade treatments. Rates of heating and cooling were unaffected by the autonomic blockade and we conclude that animals partially compensated for lack of differential heart rates during heating and cooling by maintaining some control over peripheral flow.
Published Version
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