Cardiovascular hormonal effects of circulating norepinephrine

The hormonal effects of circulating norepinephrine (NE) were evaluated with two-step NE infusion studies in normal volunteers. At an infusion rate that increased plasma NE 2.5-fold (approximately equivalent to the change from supine to upright posture), there were small but consistent increases in diastolic pressure (+ 5 mm Hg) and plasma renin activity (+ 13%). At the high extreme of the physiologic range (a 9-fold increase over supine basal), circulating NE caused major changes in blood pressure (+ 22/15 mm Hg), heart rate (- 7 bpm), and plasma renin activity (+ 67%). Thus, at physiologic concentrations, circulating NE should be considered to be a cardiovascular hormone as well as an index of sympathetic nervous activity.