Evidence of decreased plasma substance P levels in human essential hypertension and influence of prazosin treatment.

Patients with essential hypertension (n = 45) had significantly lower substance P plasma levels (13.6 +/- 2.30 pg/ml) in comparison with a group of 24 normotensive subjects (45.4 +/- 7.18 pg/ml) analyzed by radioimmunoassay. Prazosin treatment for 2 weeks with 4.5 mg/day enhanced the substance P plasma level depending on its antihypertensive effect. Norepinephrine concentration in plasma was also elevated by prazosin. Dipeptidylpeptidase IV, dopamine-beta-hydroxylase and plasma renin activity were not changed significantly. The results indicate the participation of substance P in pathophysiological processes of human essential hypertension.