Arterial Noradrenaline Concentration during Exercise in Relation to the Relative Work Levels

The noradrenaline (NA) levels in arterial blood plasma were followed at rest and during increasing muscular exercise in 5 healthy men. The levels were found to be significantly correlated to the oxygen consumption, measured at submaximal and calculated at supramaximal work. The NA levels increased slowly, up to about 75 % of the maximal oxygen consump tion, thereafter the NA levels increased rapidly. These increases are discussed with respect to increased sympathetic impulse flow, decreased inactivation of the circulating NA, and increased release from the nerve terminals per nerve impulse. At a work load requiring about 75 % or less of the maximal oxygen consumption the mean sympathetic impulse flow seems to be low. At the highest work loads (maximal to supramaximal) a markedly increased sympathetic impulse flow is of major importance for the rapidly increasing NA levels.