CENTRAL ANGIOTENSIN-II INDUCES THIRST-RELATED RESPONSES IN AN AMPHIBIAN

Angiotensin II (A-II), a potent inducer of thirst-related behavior in many vertebrate species, was injected into the third ventricle of the brain of the spadefoot toad, Scaphiopus couchii. Following injection o f 10 ng A-II the animals demonstrated a significant increase in water absorption response (WR) behavior, in which toads press their ventral skin to a moist surface and absorb water by osmosis. This increase in the frequency of WR behavior was positively correlated with an increas e in water gain during a 2-hr period indicating that centrally injecte d A-II stimulates water intake by this amphibian species. We have prev iously demonstrated that WR behavior is also induced by intraperitonea l (i.p.) injections of A-II in several anuran species, including S. co uchii. Thus, amphibians, like other vertebrates, demonstrate an increa se in water intake in response to either centrally administered or cir culating A-II. A second series of experiments was conducted to determi ne whether the above response to A-II might be secondary to increases in the circulating levels of aldosterone (ALDO) or antidiuretic hormon e because the release of both of these hormones has been shown by othe rs to be stimulated by A-II. Scaphiopus couchii injected i.p. with eit her ALDO or arginine vasotocin in dosages of 1, 10, and 100 mu g/100 g body weight showed no increase in WR behavior relative to toads injec ted with saline alone. These results suggest that A-II acts directly o n the brain of S. couchii to induce WR behavior. (C) 1995 Academic Pre ss, Inc.