Vasopressin response to hyperosmotic stimulus: blood pressure effect in normal subjects and patients with impaired sympathetic system.

We have investigated the interaction of plasma vasopressin and plasma catecholamines in quadriplegic patients (with severed sympathetic tracts) and compared them to others with intact sympathetic system following I.V. administration of a hyperosmolar radiocontrast agent during a routine diagnostic pyelography. Baseline systolic and diastolic pressure as well as plasma norepinephrine were significantly lower in the quadriplegic subjects. At 5 minutes after administration of the hyperosmolar solution, systolic and diastolic pressure as well as plasma vasopressin rose in the quadriplegic subjects but not in normal subjects despite a significant and equal rise in serum osmolality occurring in both groups. These results demonstrate that an interaction between the two systems exists in humans: an intact sympathetic nervous system attenuates the vasopressin response to hyperosmolar stimuli and in its absence vasopressin may function as a pressor agent.