PLASMA NOREPINEPHRINE VARIATIONS CORRELATE WITH PERIPHERAL VASCULAR-RESISTANCE IN RESTING HUMANS

Plasma levels of norepinephrine (NE) vary rhythmically in humans and a nimals with an ultradian (shorter than 1 day) periodicity. We repeated ly measured plasma NE levels, blood pressure, cardiac output, and tota l peripheral resistance in nine normal resting subjects over 5 h. Plas ma NE correlated with total peripheral resistance (Z = 0.322, P < 0.00 02) and inversely with cardiac output (Z = -0.276, P < 0.0002) for the nine subjects overall. The correlations were strongest in subjects wi th the most spontaneous variability in total peripheral resistance. Th ese findings suggest that spontaneous oscillations in plasma NE levels reflect alterations in sympathetic nervous activity to resistance blo od vessels. The negative correlation between cardiac output and plasma NE levels may result from the very minor cardiac NE spillover into pl asma and the inverse relationship between cardiac output and total per ipheral resistance.