Comparison of norepinephrine and isoproterenol clearance in congestive heart failure

Congestive heart failure (CHF) is accompanied by increased sympathetic nervous activity. Previous studies have demonstrated that plasma norepinephrine (NE), a marker of sympathetic nervous activity, is elevated in CHF due to increased NE spillover into the circulation and decreased NE clearance. In this study we compared the clearance of NE and isoproterenol (ISO) in eight CHF subjects (plasma NE 601 ± 133 pg/ml), and in nine controls (plasma NE 285 ± 53 pg/ml) by using steady-state infusions of tritiated NE ([³H]NE) and tritiated ISO ([³H]ISO). Because ISO is not a substrate of neuronal reuptake but is removed from the circulation in a way that is similar to NE after neuronal reuptake blockade with desipramine, ISO clearance may permit a gross estimation of non-neuronal uptake of circulating NE. The NE clearance was lower in CHF than in the control group (CHF 1.25 ± 0.13, controls 2.04 ± 0.22 l · min^-1 · m^-2; P = 0.009). The ISO clearance was reduced similarly in CHF (CHF 0.90 ± 0.09, controls 1.59 ± 0.12 l · min^-1 · m^-2; P < 0.001). Because the ratio of ISO to NE clearance was similar in both groups, our findings suggest that a low cardiac output in CHF decreases the availability of circulating catecholamines to tissue elimination sites.