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Venous versus arterial forearm catecholamines as an index of overall sympatho-adrenomedullary activity.

The metabolism of norepinephrine (NE) and epinephrine (EPI) in peripheral tissues limits the use of venous plasma levels of these parameters as an index of overall sympathetic or adrenomedullary activity. Therefore venous (deep antecubital vein) and arterial (brachial artery) concentrations of NE and EPI were compared in 16 hypertensive subjects. NE and EPI were determined after 30 min supine rest, and immediately before and after isometric exercise, cold provocation, head-up tilting (OST) and Stroop's colour word test (CWT). At rest venous NE exceeds arterial NE. Assuming similar fractional extractions (FE) of NE and EPI, 46 +/- 14% (mean +/- SD) of venous NE appeared to be produced locally. Despite this considerable local production venous and arterial levels of NE were closely correlated (r = 0.92). At rest venous EPI was 42 +/- 13% lower than arterial EPI, but since the interindividual variation of the FE of EPI was relatively small and independent of arterial levels, venous and arterial levels were also closely correlated (r = 0.82). All four tests caused an increase in arterial and venous NE, whereas EPI did not change. Responses of arterial and venous NE were only correlated after OST and CWT. It is concluded that at rest, but not invariably so during different forms of sympatho-adrenal activation, arterial plasma concentrations of NE and EPI can be substituted for by their respective venous equivalents.