Vasopressin, fluid, and electrolyte response to chronic angiotensin II infusion

The chronic interrelationships between blood-borne angiotensin (AII), plasma arginine vasopressin (AVP), fluid and electrolyte balance, and mean arterial pressure (AP) were studied in mongrel dogs by continuous intravenous infusion of AII for 7 days. Two groups of dogs were infused: group 1 and group 2 received 5.0 and 20.0 ng AII . kg-1 . min-1, respectively, and each were studied first on ad lib H2O intake and then several weeks later with "fixed" water intake. Plasma AVP was determined utilizing a sensitive radioimmunoassay procedure described herein, Group 1 (5.0 ng AII): AP rose to a steady-state level nearly 20 mmHg above control by the 3rd day of AII infusion with both ad lib and "fixed" H2O intake. With ad lib H2O, AVP was chronically unchanged while with fixed H2O a significant decrease had occurred by the 2nd day of AII infusion. Plasma Na and osmolality were not significantly changed in either state. Group 2 (20.0 ng AII): AP rose nearly 40 mmHg above control by the 3rd day of infusion with both ad lib and fixed water intake. AVP did not change significantly from a control of 0.8 microU/ml throughout AII infusion with ad lib H2O intake but drinking was more than doubled. With fixed H2O intake, plasma AVP rose from a control of 0.8 microU/ml to an average of 1.3 microU/ml over the last 4 days of AII infusion. A negative correlation was obtained between the "cumulative H2O balance" and plasma AVP obtained during AII infusion. We conclude first that circulating AII is not directly involved in the long-term control of AVP secretion and, second, neither AVP nor enhanced drinking contributes significantly to AII-induced hypertension.