Age-related augmentation of plasma catecholamines during dynamic exercise in healthy males

Although plasma norepinephrine (NE) increases with age in response to a variety of submaximal adrenergic stimuli, the effect of age on plasma catecholamine levels during maximal aerobic effort and during submaximal work at a fixed percent of peak O₂ consumption (V̇(O₂) is unknown. We therefore measured NE, epinephrine (E), and V̇(O₂) at rest and during graded maximal treadmill exercise in 24 healthy male volunteers (ages 22-77 yr) from the Baltimore Longitudinal Study of Aging who were rigorously screened to exclude the presence of cardiovascular disease. At rest neither heart rate (HR) nor V̇(O₂) were age related. Resting NE (pg/ml) was not age related, but resting E (pg/ml) was higher in male subjects 68-77 yr old (group III) than in those aged 22-37 (group I) or 44-55 yr (group II), P < 0.01. Maximal HR (beats/min) showed a strong inverse relationship to age (203.5-0.65 age, r = -0.80, P < 0.001). Peak V̇O₂ in milliliters per kilogram total body weight per minute decreased with age (47.7 - 0.23 age, r = -0.71, P < 0.001). At maximal effort both NE (P < 0.01) and E (P < 0.05) were higher in group III than in either of the younger groups. At submaximal work levels NE and E also increased with age, and when normalized for relative effort at loads between 45 and 80% of peak V̇(O₂) both NE and E were higher in the group III male subjects, although statistical significance was reached for NE (P < 0.01) but not for E (P = 0.09). Thus, for any relative level of aerobic stress incurred by healthy males during treadmill exercise, plasma catecholamines are higher in the elderly.