AGE-RELATED INCREASE IN MUSCLE SYMPATHETIC-NERVE ACTIVITY IS ASSOCIATED WITH ABDOMINAL ADIPOSITY

Tonic sympathetic nerve activity (SNA) increases with age, but the mec hanisms are unknown. There is evidence that SNA is positively related to total and abdominal body fat, which also increase with age. We test ed the hypotheses that I) the elevation in SNA with age is partially a ccounted for by higher abdominal and/or total body fat and 2) skeletal muscle is a target of the adiposity-related sympathetic effects. Dire ct microneurographic recordings of skeletal muscle SNA (MSNA) were obt ained during supine rest in 16 older(64 +/- 1 yr,means +/- SE) and 16 young(24 +/- 1 yr) adult males. Central body fat was estimated by wais t circumference (WC) and fat mass (FM) by hydrostatic weight. MSNA, WC , and FM were higher in the older vs. young males (44 +/- 2 vs. 22 +/- 2 bursts/min, 91 +/- 2 vs. 79 +/- 1 cm, and 19 +/- 2 vs. 9 +/- 1 kg, respectively; all P < 0.0001). Although univariate correlations were h igh for MSNA and both WC (r = 0.77) and FM (r = 0.75), stepwise multip le regression analysis revealed WC to be the best predictor of MSNA (R -2 = 0.60, P < 0.0001), with FM explaining only an additional 2% of th e variance (not significant). Statistically covarying for WC reduced b ut did not eliminate the difference in adjusted age-group means for MS NA (39 +/- 3 vs. 26 +/- 2 bursts/min, P = 0.003). We conclude that I)t he elevated SNA in older adults is partially related to higher body fa t, particularly in the abdominal region, and 2) skeletal muscle is a t arget of the adiposity-related sympathetic effects observed with aging .