Cutaneous diffusing capacity increases during hypoxia in cold submerged bullfrogs (Rana catesbeiana)

Gas exchange through amphibian skin appears to be primarily diffusion limited; manipulating cutaneous diffusing capacity for oxygen (DO2) may therefore be an important means of regulating cutaneous oxygen uptake (MO2). To test this hypothesis, curarized, cannulated bullfrogs were submerged and exposed to progressive aquatic hypoxia at 5 degrees C, conditions under which all O2 uptake is cutaneous and regulation of cutaneous gas exchange can be expected to be most evident. In normoxic 5 degrees C water, arterial PO2 was low (26 Torr) and the PO2 gradient across the skin was high (114 Torr). MO2 was constant as ambient PO2 decreased from 140 to 80 Torr. The PO2 gradient across the skin decreased 40% (from 114 to 68 Torr) and DO2 increased 40% (from 36 to 49 pmol.g-1.min-1.Torr-1 over this range of ambient PO2. DO2 almost doubled in severe hypoxia (PO2 30 Torr) compared to normoxia. Increased cutaneous DO2 thus helps maintain cutaneous MO2 and arterial O2 saturation in the face of environmental hypoxia.