Relations of total and abdominal adiposity to muscle sympathetic nerve activity in healthy older males

OBJECTIVES: We recently reported that skeletal muscle sympathetic nerve activity (MSNA) is related to total body and abdominal fatness in a pooled population of young and older males. Both MSNA and adiposity increase with age. Thus, it is not clear if the relation between MSNA and adiposity exists among older adults and if the age-related increase in MSNA is explained by increases in adiposity. We therefore tested the hypotheses that: 1) among older men, those with higher total body fatness and abdominal adiposity have higher MSNA and 2) MSNA is not different in healthy young and older men with similar total body and/or abdominal fatness. DESIGN: Older healthy men (63 +/- 1 y) were separated into higher and lower groups of body fat (26.9 +/- 0.8%, n = 9 vs 21.3 +/- 1.1, n = 10; P < 0.0001) and waist circumference (96.4 +/- 3.5 cm, n = 8 vs 86.2 +/- 1.5, n = 8; P < 0.01). Younger controls (26 +/- 1 y) were then matched with those in the older-lower groups for %body fat (21 +/- 1.1%, n = 10) or waist circumference (86.2 +/- 0.8 cm, n = 10). MEASUREMENTS: Total body fat was determined by hydrodensitometry, abdominal adiposity by waist circumference and resting MSNA by microneurography. RESULTS: Among the older subjects those in the higher %body fat and waist circumference groups had higher (P < 0.02) MSNA (47 +/- 3 and 48 +/- 4 bursts/min, respectively) than those in the lower groups (37 +/- 2 and 38 +/- 3 bursts/min). MSNA was directly related to %body fat (r = 0.52, P = 0.03) and waist circumference (r = 0.64, P = 0.007) in the older groups. MSNA was greater (P < 0.001) in the older-lower groups than in the young controls matched for %body fat (23 +/- 2 bursts/min) or waist circumference (24 +/- 3 bursts/min). CONCLUSIONS: 1) among healthy older men, higher levels of total body and/or abdominal adiposity are associated with higher levels of MSNA and 2) the age-related elevation in MSNA is reduced but not abolished when differences in adiposity are eliminated.