Exercise-induced changes in plasma catecholamines and neuropeptide Y: relation to age and sampling times.

Plasma norepinephrine (NE), epinephrine (E), and neuropeptide Y (NPY) were evaluated in seven young (median age 29 yr, range 21-31) and seven elderly (median age 61 yr, range 51-72) healthy subjects. They were all nonsmokers and had never smoked. Basal values and the initial increase in plasma NE and E during exercise at 75% of maximal work load were identical in the two groups. After 5 min of exercise at this load, plasma NE and E remained constant in the elderly but were still increasing in the young subjects. Plasma NE and E increased to significantly higher values after 15 min in the young subjects: 1.68 +/- 0.18 vs. 0.92 +/- 0.11 ng/ml (NE) and 0.136 +/- 0.012 vs. 0.061 +/- 0.013 ng/ml (E). Basal plasma NPY was highest at rest and increased only during exercise in the young subjects. Our results demonstrate that in nonsmokers aging is not associated with increased plasma NE levels. The blood pressure response to exercise was the same in both groups, suggesting that the increase in the sympathetic activity was adequate in the elderly. Alternatively, the higher increase in sympathetic activity in the young subjects may be attributed to their higher work capacity.