Cardiopulmonary blood volume and plasma renin activity in normal and hypertensive humans.

Plasma renin activity (PRA) and systemic and forearm hemodynamics were studied during acute changes in cardiopulmonary blood volume and central venous pressure in 20 subjects, including 9 normotensive controls and 11 essential hypertensive patients of the same age. Changes in cardiopulmonary blood volume and central venous pressure were induced by a "head-down" tilt and thigh-cuff inflation. Blood pressure, pulse pressure, and heart rate did not change during cardiopulmonary blood volume variations, whereas significant changes in cardiac output, forearm blood flow, and PRA were observed. A significant negative correlation between cardiopulmonary blood volume (CPBV) and PRA existed, and slope of this correlation of delta PRA/delta CPBV was estimated as a sensitivity index of control of renin release. Sensitivity of neural control of renin release was not statistically different in normal subjects and hypertensive patients. In two groups, sensitivity of this reflex mechanism similarly decreased with age. Aging seems to be an important factor influencing the sensitivity of neural control of renin release, both in normal and essential hypertensive humans.