SYMPATHETIC ACTIVITY INCREASES WITH AGE - RELATIONSHIP TO BLOOD-FLOW VOLUME AND LONG-TERM SMOKING

Basal venous plasma noradrenaline and muscle sympathetic nervous activ ity both increase with age. It has been reported that during exercise venous plasma noradrenaline increased more in elderly subjects both at the same relative as well as the same absolute work load, compared to younger subjects. Recent studies have shown that increased basal leve ls of plasma noradrenaline in elderly subjects were confined to elderl y long-term smokers, whereas values in elderly non-smokers and young s mokers were not different from values obtained in young non-smokers. A t present, the pathophysiological mechanism of increased levels of bas al plasma noradrenaline in long-term smokers has not been clarified, b ut cardiac output and total blood volume were not different in smokers and non-smokers. This may be due to a reduced sensitivity of alpha-ad renoceptors to noradrenaline or a compensatory mechanism to vascular d ilatation induced by chronic smoking. Reported values of increases in plasma noradrenaline during exercise are conflicting. However, recent studies have shown that the increase in plasma noradrenaline was not d ifferent in young and elderly subjects when correcting for the general ly lower physical fitness in the latter group. During exercise at rela tively high work loads, plasma noradrenaline increased more in young t han in elderly subjects. This may be explained by lack of a continuous increase in plasma noradrenaline during exercise in elderly subjects.