Age and gender influence muscle sympathetic nerve activity at rest in healthy humans.

Abstract

Muscle sympathetic nerve activity at rest increases with age in humans. The respective influences of the aging process per se and gender on this increase and whether age and gender effects on muscle sympathetic nerve activity can be identified with plasma norepinephrine concentrations, however, have not been established. To examine these issues, nine young women (aged 24±1 years; mean±SEM), eight young men (aged 26±1 years), seven older women (aged 63±1 years), and eight older men (aged 66±1 years) were studied. All were healthy, normotensive (blood pressure < 140/90 mm Hg), nonobese (<20% above ideal weight), unmedicated, nonsmokers engaged in minimal to recreational levels of chronic physical activity. Arterial blood pressure (manual sphygmomanometry, brachial artery), heart rate, muscle sympathetic nerve activity (peroneal microneurography), and antecubital venous plasma norepinephrine concentrations (radioenzymatic assay) were determined during quiet supine resting conditions. Body weight was higher in men, but there were no age-related differences, whereas estimated body fat (sum of skinfolds) was higher in women and in the older groups (p<0.05). Estimated daily energy expenditure, arterial blood pressure, and heart rate were not different among the groups. Both muscle sympathetic nerve activity burst frequency and burst incidence at rest were progressively higher in the young women, young men, older women, and older men (10±l versus 18±2 versus 25±3 versus 39±5 bursts/min and 16±1 versus 30±4 versus 40±3 versus 61±6 bursts/100 heartbeats, respectively; all p<0.05 versus each other). In contrast, average levels of plasma norepinephrine concentrations were not different among the groups. There was, however, a positive relation between plasma norepinephrine concentrations and muscle sympathetic nerve activity (r=0.65; p<0.0003) when the individual data were pooled. There were no strong or consistent associations between muscle sympathetic nerve activity and any other variable. We conclude that the rise in muscle sympathetic nerve activity with aging in resting humans appears to be independent of age-related differences in ischemic heart disease, obesity, chronic physical activity, or arterial blood pressure, and thus is likely related to some factor associated with the aging process per se. Gender, however, appears to be an important determinant of muscle sympathetic nerve activity at rest in both young and older humans. Finally, the age-and gender-specific influences on muscle sympathetic nerve activity are not necessarily reflected by plasma norepinephrine concentrations. {Hypertension 1993^21:498-503) KEY WORDS • sympathetic nervous system • aging • gender

The effect of gender on the sympathetic nerve hyperactivity of essential hypertension

“…Thus, individual patients of the groups were Caucasians and were examined using the same protocol, under similar laboratory conditions, while avoiding the influence of age, dietary intake, body weight, large meal or visceral distension factors, which are known to affect sympathetic activity or its control. 14,15,17,19,[30][31][32][33][34] We also quantified the mean frequency of s-MSNA units and that of MSNA multiunits. The former was considered as an index of the mean frequency of efferent sympathetic nerve …”

“…4,14 On the other hand, previously reported findings in normotensive populations have not been consistent as to whether MSNA levels are different between men and women. Young women may have a lower [15][16][17][18][19] or similar 20,21 level of resting MSNA relative to young men. Also, older women may have a lower 15 or similar 17,19 level of resting MSNA relative to older men.…”

Disparity of autonomic control in type 2 diabetes mellitus

“…Our study design also avoided confounding effects when comparing patients with type 2 diabetes with control subjects. We avoided the potential effects of race, age, body weight, time of day, dietary sodium intake, arterial blood pressure level, visceral distension, alcohol, nicotine and exercise on the autonomic drive [36,[38][39][40][41][42][43][44][45][46]. These criteria were satisfied by closely matching the three groups and by using the same protocol for all subjects.…”

Sympathetic Vascular Tone in Human Obesity

“…Experimental evidence indicates that aging contributes substantially to the progressive elevation of mSNA [Fagius & Wallin, 1993;Ng et al, 1993]. Because of this observation, the confounding effect of aging while comparing normotensive and hypertensive subjects could not be excluded.…”

“…Sympathetic nerve activity to skeletal muscle tends to be lower in women and higher in the elderly [Ng et al, 1993]. Thus, microneurographic studies should ideally be controlled for these variables.…”