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.