Influence of temperature acclimation on Oxygen consumption, Haemodymanics and oxygen transport in bullfrogs

Abstract

The effect of temperaure acclimation on oxygen transport by the circulation was studied by comparing the responses of bullfrogs held at 5 or 20ºC for several weeks during the winter. Blood flow (Q) to the hind legs of restrained unanaesthetized frogs was measured at 20ºC 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 5ºC resulted in a significant decrease in V(O2) of normal frogs as compared with 20ºC-acclimated frogs, and a reduction in T(O2)D due to a significantly lower Q. Blood flow to the hind legs measured at 20ºC averaged 33.9 ml kg-1 min-1 in 5ºC-acclimated frogs, and 50.9 ml kg-1 min-1 in 20ºC-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).