Sympathetic neural reactivity to stress does not increase with age in healthy humans

Abstract

Sympathetic nervous system reactivity to stress is though to increase with age in humans. We tested this hypothesis by recording postganglionic sympathetic nerve activity to skeletal muscle (MSNA) (peroneal microneurography) and by measuring plasma norepinephrine concentrations (PNE), heart rate, and arterial pressure before (prestress control) and during cognitive challenge (mental arithmetic and colored word test), thermal stress (i.e., the cold pressor test), and exhaustive isometric handgrip exercise (40% of maximum voluntary force)/postexercise ischemia in 15 older (60-74 yr, mean +/- SE = 64 +/- 1) and 15 young (19-30 yr, mean +/- SE = 25 +/- 1) healthy men and women (8 males, 7 females each). The initial prestress control level of MSNA was higher in the older subjects (P < 0.01 vs. young), but there were no significant differences for PNE, heart rate, or arterial pressure. The MSNA and PNE responses to mental stress were small and not different in the two groups. MSNA and PNE increased markedly in response to the cold pressor test and isometric handgrip exercise/post exercise ischemia in both groups. The absolute unit increases in MSNA were similar in the two groups, but the relative (percentage) increases were actually smaller in the older subjects (P < 0.05 vs. young) due to their elevated baseline levels. The stress-evoked increases in arterial pressure were similar in the groups, but the older subjects tended to demonstrate smaller increases in heart rate. In general, no gender differences were noted in either age group. These findings fail to support the long-held concept that stress-induced sympathetic nervous system stimulation becomes exaggerated with age. Thus, sympathetic neural hyperreactivity does not appear to be a fundamental property of the aging process in humans.

Aging and the Exercise Pressor Reflex in Humans

“…17 A prior report has suggested that attenuated MSNA response to handgrip in the aged is due to higher resting MSNA and not to muscle reflex attenuation per se. 18 Our study also demonstrates higher resting MSNA in older subjects. 18 However, we have shown that progressive ischemia used to progressively and systematically engage the muscle reflex led to multiple attenuated indices of MSNA ( Figure 1D through 1G) as well as BP in the aged ( Figure 1A).…”

“…18 Our study also demonstrates higher resting MSNA in older subjects. 18 However, we have shown that progressive ischemia used to progressively and systematically engage the muscle reflex led to multiple attenuated indices of MSNA ( Figure 1D through 1G) as well as BP in the aged ( Figure 1A). The fact that both BP and MSNA were attenuated and the fact that data in Figure 1 were compared with E1 and not baseline leads us to believe that differences in resting MSNA between young and old subjects cannot totally explain our findings.…”

Muscle sympathetic nerve activity during cold stress and isometric exercise in healthy older adults

“…Studies of adults exercising in cold environments are few and generally limited to those using varied methodology exploring either the control of cutaneous blood flow during exercise (46) or the performancerelated effects of cold acclimation (17,57,61). At thermoneutral temperatures, older adults exhibit either similar (21,40,49) or blunted (26,33,48) increases in MSNA and BP during static HG compared with the increases demonstrated in young adults. Consistent with these previous studies, we report no agerelated differences in the sympathetic and pressor responses to static HG at baseline (i.e., mean T sk 34.0°C).…”

“…This effect may be mediated via impairments in the sympathetic control of the cardiovascular system and BP regulation during combined cold stress and isometric exercise. At thermoneutral temperatures (ϳ20 -22°C), the increases in MSNA during isometric handgrip (HG) in healthy older adults have been shown to be either similar to (21,40,49) or less than (26, 33, 48) the increases observed in young adults. Studies of both young and older subjects exercising in cold environments are surprisingly limited.…”

Does Aging Cause Women to be More Sympathetic Than Men?

“…1 Moreover, reduced sympathetic nervous system activity, augmented sympathetic inhibition, and higher cardiac vagal tone in women, compared with men, have all been described. [1][2][3][4][5] Finally, the responsiveness to stressor stimuli may be diminished in women compared with men as well. 1 In summary, despite the overall increase in sympathetic activity with aging, for any given age women seem to have less sympathetic drive than men.…”