Different norepinephrine disappearance rate in venous and arterial plasma in man

The disappearance of norepinephrine in both arterial (radial) and venous (antecubital) plasma was studied in five patients with mild essential hypertension following isometric exercise and norepinephrine infusion. Arterial levels of epinephrine throughout the study and of norepinephrine during norepinephrine infusion were consistently higher than venous levels, indicating that both amines are removed by passage through the forearm. Following infusion the disappearance rate of norepinephrine from arterial plasma was faster than from venous plasma. After isometric exercise there was a delay in fall of venous levels, consistent with a delayed efflux of norepinephrine from local tissues. Arterial plasma levels probably reflect total body contribution whereas venous plasma levels presumably reflect additional local removal and/or release from the forearm.