Plasma norepinephrine response to exercise before and after training in humans

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Abstract
Plasma norepinephrine (NE) concentration was measured by means of a sensitive radioenzymatic assay in blood collected from an antecubital vein in 10 healthy men (37 .+-. 2 yr, mean .+-. SE). The subjects were evaluated at rest and during exercise before and after a 20-wk training program on bicycle ergometer (three 30-min sessions per wk at 80% of maximal heart rate). Following the training program, maximal O2 uptake increased significantly from 33 .+-. 2 to 42 .+-. 1 ml .cntdot. kg-1 .cntdot. min-1. Resting plasma NE remained unchanged after training (167 .+-. 38 before vs. 185 .+-. 29 pg .cntdot. ml-1 after training). For a given absolute work load (735 .+-. 51 kg .cntdot. m .cntdot. min-1), the sympathetic nervous response was lower after training as reflected by the decrease in NE concentration (1371 .+-. 286 vs. 687 .+-. 64 pg .cntdot. ml-1). At the same relative work load (heart rate: 158 .+-. 5 before and 157 .+-. 5 beats .cntdot. min-1 after training) plasma NE concentration was unchanged after training (1371 .+-. 286 vs. 1729 .+-. 371 pg .cntdot. ml-1). Sympathetic nervous activity is closely linked to the exercise demands; it remains constant in relation to the relative work load.