Abstract
The effect of temperaure acclimation on oxygen transport by the circulation was studied by comparing the responses of bullfrogs held at 5 or 20�C for several weeks during the winter. Blood flow (Q) to the hind legs of restrained unanaesthetized frogs was measured at 20�C with an electromagnetic flow meter. Measurements of arterial and venous pressure and oxygen content were made simultaneously with the flow determinations, and oxygen delivery to the hind legs [T(O2)D] was calculated as the product of Q and arteriovenous oxygen difference. Determinations of T(O2)D are compared with values for oxygen consumption [V(O2)] of normal frogs measured in a closed-circuit respirometer. Acclimation to 5�C resulted in a significant decrease in V(O2) of normal frogs as compared with 20�C-acclimated frogs, and a reduction in T(O2)D due to a significantly lower Q. Blood flow to the hind legs measured at 20�C averaged 33.9 ml kg-1 min-1 in 5�C-acclimated frogs, and 50.9 ml kg-1 min-1 in 20�C-acclimated frogs. Arteriovenous oxygen difference was not significantly different in warm and cold acclimated frogs, averaging 2.28 and 2.78 ml per 100 ml, respectively. T(O2)D averaged 53.1 and 68.8 ul g-1 h-1 for cold and warm acclimated frogs, respectively. Thus bullfrogs respond to thermally induced alterations in oxygen consumption by altering blood flow, arteriovenous oxygen difference remaining unchanged. Values of Q determined for bullfrogs largely represent Q to skeletal muscle and fall within the range of values reported for resting skeletal muscle Q of mammals. These data confirm earlier reports which suggested that amphibia have higher rates of blood flow than would be expected from known rates of V(O2).
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