Norepinephrine release in essential hypertension.

Supine basal plasma norepinephrine was higher in a group of newly diagnosed patients with mild essential hypertension than in age- and sex-matched "laboratory-naive" volunteers. Sympathetic activation by exercise and change of posture increased plasma norepinephrine in both groups, with a tendency toward higher values in the hypertensive patients, but norepinephrine clearance was slower and half-life longer in these patients. Thus the estimate of neuronal norepinephrine release obtained by correction of plasma norepinephrine for individual values of clearance was in the same range in both groups. Plasma norepinephrine was lower in younger "laboratory-adapted" subjects than in the "laboratory-naive" normotensive subjects, but clearance was in the same range in both. Thus, variations in kinetics may contribute to differences in plasma norepinephrine between patients with essential hypertension and matched controls. In contrast, the lower plasma concentration of norepinephrine in "laboratory-adapted" than in "laboratory-naive" controls appears to reflect a lower level of sympathetic activity in the former.