The Effects of Age on the Plasma Catecholamine Response to Mental Stress in Man*

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Abstract
To determine if sympathetic nervous system activity is heightened during psychological stress in older adults, plasma norepinephrine (NE), epinephrine (EPI), heart rate, and blood pressure were measured in 10 healthy old (mean age, 68.5 yr) men and 10 healthy young (mean age, 26.6 yr) men during a 12-min mental stress test. Basal NE was higher in old than in young men (400 .+-. 33 vs. 286 .+-. 32 pg/ml; P < 0.01). Consistent significant increases in plasma NE occurred only in the elderly, and the mean increases (.DELTA.) in NE during testing were significantly greater (P < 0.01) in the old than in the young men. Compared to basal levels, plasma EPI increased by 2 min in both young (.DELTA.EPI, 50 .+-. 20 pg/ml; P < 0.02) and old subjects (.DELTA.EPI, 41 .+-. 11; P < 0.01) and remained significantly increased throughout the test. There was no difference in either basal or .DELTA.EPI between young and old men. Heart rate and blood pressure were significantly increased throughout testing for both age groups. Although the .DELTA. blood pressure during testing tended to be greater in the old men, this difference was not statistically significant. Conversely, the .DELTA. heart rate was greater in the young subjects (P < 0.005). Since EPI increases were similar in old and young men, mental stress-related adrenomedullary activation does not appear to change the age. The increased plasma NE response in the elderly suggests that they have heightened activity of postganglionic sympathetic neurons during psychological stress.

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