Effects of environmental O2 on blood flow and diffusing capacity in amphibian skin

The effects of local environmental PO2 on cutaneous blood flow (Q) and the membrane diffusing capacity of the skin (D) were investigated in the leopard frog, Rana pipiens, and the lungless salamander, Desmognathus quadramaculatus. Halothane anesthetized animals were equilibrated with Freon-22 (Fr) and acetylene (Ac) in a box. A gas mixture containing either 0, 20 or 40% O2, respectively, in N2 and initially free of Fr and Ac was drawn through a small sample chamber on the abdomen. The excretion of Fr and Ac into the chamber was analyzed with a mass spectrometer. These conditions allowed the determination of the cutaneous conductance to Fr (GFr) and Ac (GAc) at the 3 levels of local environmental O2. GFr and GAc of the isolated skin and the blood solubilities of the 2 gases were also determined. To estimate Q, DAc and DFr, the data were analyzed with a homogeneous single capillary model. In the frog, Q varied directly with sample chamber [O2], but chamber [O2] had no effect on D. In the salamander, O2 had no effect on either Q or D. The results indicate that regulation of cutaneous gas exchange in the frog by local environmental O2 only involves alterations in Q. Similar control of cutaneous gas exchange is absent in the lungless salamander.