GENDER DIFFERENCES IN MUSCLE SYMPATHETIC-NERVE ACTIVITY - EFFECT OF BODY-FAT DISTRIBUTION

Muscle sympathetic nerve activity (MSNA) has been correlated with perc ent body fat (%BF) in males. Because MSNA is typically lower and %BF h igher in females, we tested whether this relationship could be general ized to females. Because abdominal-visceral body fat in men may be res ponsible for elevated sympathetic activity, we hypothesized that an es timate [waist-to-thigh ratio (W/T)] would correlate positively with MS NA in both genders and account for higher MSNA in males. Microneurogra phy, hydrodensitometry, and W/T measures were obtained in 14 males and 14 females with a large range of %BF and W/T. Regression analyses rev ealed positive correlations between MSNA and %BF in males (r = 0.55, P = 0.04) and in females (r = 0.63, P = 0.02), with no difference in th e slopes of the regression lines but a higher intercept in males (P < 0.01). When genders were pooled, MSNA and WPT were correlated (r = 0.6 8, P < 0.0001); this positive correlation was also found in males (r = 0.57, P = 0.04) but not as strongly in females (r = 0.49, P = 0.07). Forward stepwise multiple-regression analysis using %BF, W/T, gender, and age indicated that W/T was the primary factor related to MSNA (R(2 ) = 0.46); the other factors were not independent predictors. It is co ncluded that %BF is related to MSNA in both males and females but that the regression line is shifted downward in females because of lower l evels of MSNA. W/T is a better correlate of MSNA than %BF and partiall y explains the higher MSNA in males. These findings may be relevant to the cardiovascular and metabolic disease risk associated with abdomin al obesity.