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 vari ety of stressors are influenced by age, adiposity, and exercise traini ng status. The objectives of this study were to 1) compare basal level s 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 wit h adiposity and maximal O2 uptake (VO2max) and 2) determine the extent to which the NE and E responses are altered by exercise training in o lder people. We found no significant differences in basal NE and E lev els between young and older subjects. However, the NE response to stan ding was exaggerated in older people (696 +/- 39 vs. 512 +/- 61 pg/ml; P < 0.05), whereas NE and E responses to exercise requiring approxima tely 78% of VO2max were attenuated in older people (NE: 1,444 +/- 74 v s. 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 associa ted with age (NE: r = -0.38; E: r = -0.46; both P < 0.05) and VO2max ( 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 complet ed 9 mo of exercise training, the increases in NE and E during exercis e at the same absolute intensity were 39 and 57% lower, respectively. These changes correlated with the smaller increases in heart rate duri ng exercise and with the degree of improvement in VO2max. The results indicate that 1) compared with young people, older people have a blunt ed catecholamine response to exercise at a given relative intensity, a nd 2) exercise training results in a marked reduction in metabolic and hemodynamic stress during exercise at a given absolute intensity in o lder people.