Regulation of cutaneous gas exchange by environmental O2 and CO2 in the frog

The effects of environmental PO2 and PCO2 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 and Fr, was drawn through a small test chamber placed on the abdomen. The excretion of Fr, Ha and CO2 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 [O2] produced concentration-dependent increases in the excretion of all gases measured. Lowering chamber [O2] reduced gas excretion. Increasing chamber [CO2] to 5% decreased the excretion of Fr and Ha. Increasing box [O2] to 86.5% while keeping sample chamber [O2] constant at 21% decreased gas excretion into the chamber. Selectively raising box [CO2] 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 [O2] directly above that portion of skin, and inversely related to the [O2] over adjacent skin. This regional perfusion-O2 matching may act to optimize total cutaneous gas exchange in the frog. In addition, CO2 may be an important regulator of cutaneous blood flow distribution.