Long-term influence of vasopressin on the control of arterial blood pressure independent of volume changes.

Studies were performed to ascertain the extent to which arterial blood pressure, and fluid and electrolyte changes seen with chronic elevations of plasma vasopressin (AVP) were caused by volume expansion or some other more direct cardiovascular or neural interactions of AVP. Group 1 (n = 7) dogs were infused with AVP (0.36 ng/kg/min) while total body weight and volume were maintained at a constant level by the use of an electronically controlled servocontrol system. Dogs in Group 2 (n = 6) were permitted to drink ad libitum during AVP infusion. Group 3 (n = 6) dogs were maintained with a constant level of H2O intake by intravenous infusion during two weeks AVP administration. The results indicate that chronic elevation of plasma AVP resulted in a prolonged elevation of arterial pressure only when there was a large expansion of total body water. Dogs with total body volume servocontrolled to a constant level (Group 1) and those with a moderate increase in volume (Group 2) exhibited no measureable change in mean arterial pressure during AVP infusion. Dogs with Fixed H2O intake (Group 3) retained a large fluid volume. They exhibited renal escape from AVP and large decreases of plasma osmolality, sodium concentration and plasma renin activity. With as libitum drinking (Group 2), only mild volume expansion occurred which resulted in a partial escape from the volume-retaining effects and smaller decreases of plasma osmolality and sodium. When total body weight and volume were servocontrolled to a constant level, no renal escape occurred and hype-osmolality, hyponatraemia and hyporeninaemia were not observed (Group 1).(ABSTRACT TRUNCATED AT 250 WORDS)