Subpressor angiotensin II infusions do not stimulate sympathetic activity in humans.

Angiotensin II (ANG II) exerts significant direct and indirect pressor and chronotropic effects in experimental animals. The indirect effects have been shown to be due to interactions with the sympathetic nervous system at several levels. To test the hypothesis that ANG II in subpressor doses enhances the activity of the sympathetic nervous system in humans either at rest or in response to a stimulus from baroreceptor unloading, we measured mean arterial pressure (MAP), heart rate (HR), plasma norepinephrine (NE), and plasma NE kinetics during infusions of ANG II at 2 ng.kg-1. min-1 [or 5% dextrose in water (D5/W) control in six healthy volunteers in the supine position and during 60 degrees head-up tilt. No changes in any measured variable occurred during either infusion in the supine position. During upright tilt with D5/W, HR increased (58 +/- 8.4 to 68 +/- 7.7 beats/min, P less than 0.005), MAP rose slightly (90 +/- 3.9 to 94 +/- 4.0 mmHg, P less than 0.005), and plasma NE increased (213 +/- 3.8 to 366 +/- 83 pg/ml, P less than 0.005). The responses of the variables to tilt during ANG II were not different from those with D5/W.(ABSTRACT TRUNCATED AT 250 WORDS)