Regional variation and control of cutaneous gas exchange in bullfrogs

Previous work has demonstrated regional differences in morphometric diffusing capacity and cutaneous blood flow in anuran amphibians, leading to the prediction of a higher rate of cutaneous gas exchange across the dorsal skin of bullfrogs. Regionally measured cutaneous O2 and CO2 flux rates (MO2 and MCO2) support this prediction: flux rates across the dorsal skin are 15-32% greater than across the ventral skin in both pulmonary ventilating and apneic (anesthetized) bullfrogs. The rates of cutaneous gas exchange were much greater in anesthetized frogs; however, MO2 and MCO2 did not increase in parallel, which decreased the cutaneous respiratory exchange ratio from 3.5 to 2.0 in apneic frogs. Regional differentiation in cutaneous gas exchange suggests the possibility of independent regulation; however, cutaneous MCO2 varied little in response to changes in O2 content above these regions, neither in the anesthetized nor awake bullfrogs. The bullfrogs are able to increase whole body cutaneous gas flux during prolonged apnea but were not able to respond to changes in local O2 content.