Plasma substance P levels in normotensive and hypertensive subjects.

Since substance P is a potent natriuretic, diuretic, and vasodilatory peptide, a radioimmunoassay for substance P was developed, and its levels measured in the plasma of normal subjects and patients with essential hypertension. The plasma substance P levels were 186+/-14 pg/ml in normal subjects and 164+/-3 pg/ml in hypertensive patients. When the sodium content of their diet was reduced to 10 mEq/day, substance P levels failed to change, but plasma renin activity and urinary kallikrein increased. An acute saline infusion also failed to alter plasma substance P levels. Assuming an upright posture increased plasma renin activity, but not substance P, in both groups of subjects. Thus, it appears that substance P is not involved in the control of blood pressure, kallikrein excretion or renin release in man.