Hypertensives’ Pressor Response to Norepinephrine

Abstract

After 5 days of a 10 mEq sodium diet or 4 days of a 200 mEq sodium diet, 15 hypertensives and 11 normotensive control subjects received pressor doses of intravenous norepinephrine (NE). Analysis of pressor responses to the rate of NE infusion showed that the high salt diet sensitized subjects so that they needed less NE to raise systolic blood pressure (SBP) 20 mm Hg (P = .005). There was a complex interaction of salt intake, black race, and hypertension on NE pressor sensitivity (P = .03). Hypertensives attained lower plasma NE levels during the stepwise NE infusion, so we reanalyzed NE sensitivity in terms of the changes in plasma NE levels. This analysis also showed that during the high salt diet, subjects initiated a pressor response at lower plasma NE levels (P = .017) and raised SBP 20 mm Hg at lower NE levels (P = .007). The reanalysis showed that hypertensives initiated a pressor response at lower plasma NE levels (P = .03) and raised SBP 20 mm Hg at lower NE levels (P = .002). Plasma NE levels should provide a better guide to the concentration of NE at cardiovascular receptors than the rate of NE infusion. Analysis of pressor responses to plasma NE levels demonstrated that the hypertensives had an exaggerated pressor response to NE.