Angiotensin II elicits water seeking behavior and the water absorption response in the toad Bufo bufo

Fully hydrated toads, Bufo bufo were acclimated to a simulated terrestrial habitat, with access to shelters and water. To get from the shelters to the water, the toads had to walk across the pan of an Ohaus balance and the body weights were recorded on a computer. Toads were placed inside shelters immediately following injection of human angiotensin II (A II), Thr(8)-saralasin, or Ringer's in the dorsal lymph sac, and their behavior was recorded continuously by video surveillance. The injection doses were 1-100 microg/100 g body weight A II and 100 microg/100 g body weight saralasin dissolved in 0.1 ml Ringer's; control animals received the same volume of Ringer's. The latency from injection to the initiation of water absorption behavior (WR) was significantly shorter in both A-II- and saralasin-injected toads, compared to controls. A-II- and saralasin-injected toads also spent significantly more time in the water than controls. The bladder depots when WR was terminated were significantly larger in A-II- or saralasin-injected toads than in controls. The stimulatory action of Thr(8)-saralasin, an antagonist of A II in mammals, on WR behavior in B. bufo suggests differences in receptor structure and/or receptor distribution between amphibians and mammals.