Effects of chronic intraventricular administration of angiotensin II on drinking behavior and blood pressure

Angiotensin II was continuously infused into the lateral cerebral ventricle of rats, and the effects on daily food and water consumption, urine volume, and aortic blood pressure were studied. All was infused at a rate of 10 ng/hr for seven days, using subcutaneously implanted osmotic minipumps. An intraventricular (IVT) control group was infused with only the saline vehicle, while a third group received AII subcutaneously. IVT AII rats showed a four-fold increase in water consumption, to a mean of 171 ml/day during Days 2-4 of infusion, whereas water intake of the other groups did not change from preinfusion levels. Urine volume showed a similar pattern to water intake, increasing five-fold in the IVT AII group during Days 2-4. These measures declined during the final three days of AII infusion, but significant tolerance was not observed. Food intake decreased markedly in both saline and IVT AII groups after implantation of the pumps, but the latter resumed normal food intake more slowly than the former, and body weight remained below preinfusion levels throughout the AII period. Aortic blood pressure of the IVT AII rats showed a slight, but progressive, rise during the infusion period, but it did not significantly exceed that of the saline rats. These results indicate that continuous, low-level, intraventricular infusion of AII may markedly increase water intake without significantly increasing fluid retention or blood pressure.