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

1. When marsupial brush-tailed possums were maintained on a normal fruit and vegetable diet with access to water ad libitum, I.V. infusion of synthetic angiotensin II at rates of 0.035-3.5 mug/kg. min caused short-latency drinking in up to seven of eleven animals tested. These rates also had significant pressor effects.2. 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 second infusion 1 hr later was reduced. There was a negative correlation between the rate of infusion and the latency to drinking.3. Of six animals given access to both water and 1.8% sodium chloride solutions, five 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 mug/kg. min.4. Withdrawal of 10% of blood volume, known to stimulate renin production in the possum, caused an increase in water intake in only one of six possums.5. Infusion of isoprenaline I.V. at 20 mug/kg. min, which caused a profound fall in B.P., had no effect on drinking by all six possums.6. It is concluded that 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.