Effects of age, adiposity, and fitness level on plasma catecholamine responses to standing and exercise

The plasma norepinephrine (NE) and epinephrine (E) responses to a variety of stressors are influenced by age, adiposity, and exercise training status. The objectives of this study were to 1) compare basal levels as well as posture- and exercise-induced changes in plasma NE and E concentrations in young [25 ± 1 (SE) yr; n = 24] and older (64 ± 1 yr; n - 106) people and examine the associations of the responses with adiposity and maximal O₂ uptake (V̇O(2 max)) and 2) determine the extent to which the NE and E responses are altered by exercise training in older people. We found no significant differences in basal NE and E levels between young and older subjects. However, the NE response to standing was exaggerated in older people (696 ± 39 vs. 512 ± 61 pg/ml; P < 0.05), whereas NE and E responses to exercise requiring ~78% of V̇O(2 max) were attenuated in older people (NE: 1,444 ± 74 vs. 1,983 ± 222 pg/ml; E: 109 ± 10 vs. 228 ± 29 pg/ml; both P < 0.01). Increments in NE and E during exercise were more closely associated with age (NE: r = -0.38; E: r = -0.46; both P < 0.05) and V̇O(2 max) (NE: r = 0.43; E: r = 0.52; both P < 0.05) than with adiposity (NE: r = 0.29; E: r = -0.25; both P < 0.05). In 48 older subjects who completed 9 mo of exercise training, the increases in NE and E during exercise at the same absolute intensity were 39 and 57% lower, respectively. These changes correlated with the smaller increases in heart rate during exercise and with the degree of improvement in V̇O(2 max). The results indicate that 1) compared with young people, older people have a blunted catecholamine response to exercise at a given relative intensity, and 2) exercise training results in a marked reduction in metabolic and hemodynamic stress during exercise at a given absolute intensity in older people.