Journal Title
Title of Journal: J Comp Physiol B
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Abbravation: Journal of Comparative Physiology B
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Publisher
Springer-Verlag
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Authors: Frank Seebacher Craig E Franklin
Publish Date: 2007/07/17
Volume: 177, Issue: 8, Pages: 841-848
Abstract
Changes in blood flow are a principal mechanism of thermoregulation in vertebrates Changes in heart rate will alter blood flow although multiple demands for limited cardiac output may compromise effective thermoregulation We tested the hypothesis that regional differences in blood flow during heating and cooling can occur independently from changes in heart rate We measured heart rate and blood pressure concurrently with blood flow in the crocodile Crocodylus porosus We measured changes in blood flow by laser Doppler flowmetry and by injecting coloured microspheres All measurements were made under different heat loads with and without blocking cholinergic and βadrenergic receptors autonomic blockade Heart rates were significantly faster during heating than cooling in the control animals but not when autonomic receptors were blocked There were no significant differences in blood flow distribution between the control and autonomic blockade treatments In both treatments blood flow was directed to the dorsal skin and muscle and away from the tail and duodenum during heating When the heat source was switched off there was a redistribution of blood from the dorsal surface to the duodenum Blood flow to the leg skin and muscle and to the liver did not change significantly with thermal state Blood pressure was significantly higher during the autonomic blockade than during the control Thermal time constants of heating and cooling were unaffected by the blockade of autonomic receptors We concluded that animals partially compensated for a lack of differential heart rates during heating and cooling by redistributing blood within the body and by increasing blood pressure to increase flow Hence measures of heart rate alone are insufficient to assess physiological thermoregulation in reptiles
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