The effect of intravenous infusion of angiotensin II on drinking in the Australian marsupial Trichosurus vulpecula

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Abstract
When marsupial brush-tailed possums were maintained on a normal fruit and vegetable diet with access to water ad lib, i.v. infusion of synthetic angiotensin II at rates of 0.035-3.5 .mu.g/kg .cntdot. min caused short-latency drinking in up to 7 of 11 animals tested. These rates also had significant pressor effects. There was a positive correlation between the rate of angiotensin infusion and the percentage of tested animals which responded by drinking, as well as the amount of water drunk by such animals. The amount drunk during a 2nd infusion 1 h later was reduced. There was a negative correlation between the rate of infusion and the latency to drinking. Of 6 animals given access to both water and 1.8% NaCl solutions, 5 drank some saline during maintenance and control periods and all responded with short-latency drinking of water to infusion of angiotensin II at 0.35 .mu.g/kg .cntdot. min. Withdrawal of 10% of blood vol, known to stimulate renin production in the possum, caused an increase in water intake in only 1 of 6 possums. Infusion of isoprenaline i.v. at 20 .mu.g/kg .cntdot. min, which caused a profound fall in BP [blood pressure] had no effect on drinking by all 6 possums. These marsupials share with eutherian mammals responsiveness to a dipsogenic action of angiotensin II, which appears to be inhibited by preceding ingestion of water and potentiated by preceding ingestion of hypertonic saline. The physiological significance of this effect is uncertain.