Cutaneous blood flow during heating and cooling in the American alligator.

Nine alligators, Alligator mississippiensis, were injected with 133Xe and the clearance half times measured in response to heating and cooling. Mean half times for thermostable, heating, and cooling conditions were 12.2, 8.6, and 28.3 min, respectively, indicating cutaneous vasodilation in response to local heating and reduced blood flow during cooling. Alterations of cutaneous blood flow occurred before changes in body temperature or heart rate. Warming portions of the animal while shading the injection site resulted in reduced blood flow when heat loss occurred. Skin thickness (S in cm) was related to body mass (M in kg) as S = 0.08 M0.38. Cutaneous blood flow per unit area was found to increase with increasing body mass from approximately 0.0025 to 0.025 ml blood-cm-2 of skin-min-1 during warming and from 0.0018 to 0.0045 during cooling for the 0.18--8.6 kg animals, respectively.