Skin circulation of the frog, Rana catesbeiana: distribution and dynamics.

The volume and distribution of blood flow to the skin of the bullfrog, Rana catesbeiana, from both the pulmocutaneous and systemic arterial sources were measured. Radioactively labelled microspheres (35 +/- 5 micron) were used to map the regional distribution of each of these sources and to measure the systemic blood flow to the skin during air breathing and diving. Cutaneous artery blood flow was measured with an ultrasonic (Doppler) flowmeter. The systemic supply to the skin perfuses predominantly the limbs, while the largest cutaneous artery supply is to the back and flanks of the animal. All regions received blood from both sources. The cutaneous artery blood flow decreased during diving to approximately one-third of the pre-dive level. This decrease, however, was offset by an approximately equivalent increase in systemic blood flow to the skin during diving. These data should reconcile the decrease in pulmocutaneous blood flow and the important function of the skin as a gas exchanger during diving.