Plasma noradrenaline increases with age

Abstract

WE measured plasma noradrenaline (NA) levels in about 20 individuals who were to serve as normal control subjects and noted that older subjects tended to have higher NA levels. Extending the study to teenage and elderly subjects revealed that basal levels of plasma NA correlate with age and that the increase in plasma NA in response to stress is similarly related to age. There is considerable evidence that sensitivity to NA and NA metabolism change with increasing age. In rabbits and cats the threshold for cardiovascular response to low levels of NA decreases with old age¹. In ageing rats uptake of NA into the heart is greater than in young animals² and there is a diminished inotropic response of aged rat myocardium to a fixed concentration of NA (ref. 3). Cardiac monoamine oxidase activity increases severalfold during the life span of a rat while dopa decarboxylase decreases during the first year². In man, propranalol, which blocks β-adrenergic receptors, reduces heart rate and cardiac output during exercise, but this effect is considerably smaller in older subjects⁴. The response of heart rate to hypoxia and hypercapnia is attenuated in older men⁵.