Regulation of cutaneous gas exchange by environmental O 2 and CO 2 in the frog

Abstract

The effects of environmental P O 2 and P CO 2 on cutaneous blood flow and gas exchange were investigated in the frog, Rana pipiens. Halothane (Ha) anesthetized frogs were equilibrated with 9.5% Freon-22 (Fr), 1.1% Ha and air while placed in a box. A gas mixture, initially free of Ha of Ha and Fr, was drawn through a small test chamber placed on the abdomen. The excretion of Fr, Ha and CO 2 into the sample chamber was analyzed by a mass spectrometer. Under these conditions, changes in Fr or Ha excretion into the sample chamber reflected local changes in skin perfusion. Raising sample chamber [O 2] produced concentration-dependent increases in the excretion of all gases measured. Lowering chamber [O 2] reduced gas excretion. Increasing chamber [CO 2] to 5% decreased the excretion of Fr and Ha. Increasing box [O 2] to 86.5% while keeping sample chamber [O 2] constant at 21% decreased gas excretion into the chamber. Selectively raising box [CO 2] to 4.3% increased gas excretion into the chamber. The results indicate that regional cutaneous blood flow and gas exchange is a direct function of the [O 2] directly above that portion of skin, and inversely related to the [O 2] over adjacent skin. This regional perfusion-O 2 matching may act to optimize total cutaneous gas exchange in the frog. In addition, CO 2 may be an important regulator of cutaneous blood flow distribution.