Angiotensin II Stimulates Cutaneous Drinking in the Toad Bufo punctatus

Abstract

The renin-angiotensin system regulates drinking in many vertebrates but has not been thought to serve this function in amphibians because injections of angiotensin II (AII) have failed to stimulate either oral or cutaneous drinking. We tested the effects of intraperitoneal injections of AII on the duration of water absorption behavior and water weight gain of the red-spotted toad, Bufo punctatus. We found that doses of 1, 5, and 200 μg AII/100 g body weight significantly increased both the duration of water absorption behavior and water weight gain. The effect was eliminated by prior injection of saralasin (a specific competitive inhibitor of AII). This suggests that the mechanism that regulates hydration in amphibians is homologous to thirst mechanisms in other vertebrates and may represent an important step in the evolution of thirst in terrestrial vertebrates.