Effect of Chronic Intracerebroventricular Angiotensin II Infusion on Vasopressin Release in Rats

Abstract

Angiotensin II (AII) was infused into the lateral cerebral ventricle of rats given water, isotonic saline, or hypertonic saline ad libitum, or 40 ml water/day. Fluid intake, change in body weight, plasma [Na⁺], and plasma and pituitary arginine vasopressin (AVP) levels were measured. Isotonic saline or All (1 µg/µl saline) was infused at 1 µl/h for 5 days using osmotic minipumps. All increased fluid intake of rats given isotonic saline to drink; they consumed an average of 269 ± 25 ml/day on day 5. All infusions in rats given water or isotonic saline to drink decreased plasma [Na⁺] with no changes in plasma or pituitary AVP. However, in rats given hypertonic saline, plasma [Na⁺] remained at control levels while plasma AVP increased. In water-restricted rats, the effects of AII were intermediate: a small decrease in plasma [Na⁺] and a small increase in plasma AVP. From these results, it is suggested that although acute All administration elicits AVP release, this effect diminishes during chronic ATI infusion, coincident with reduced plasma [Na⁺].