Sympathetic neural activation in human obesity is phenotype dependent

Abstract

A series of studies focusing on the influence of body fat distribution on sympathetic neural activation (SNA) were conducted to determine 1) if muscle sympathetic nerve activity (MSNA) would be greater in men with higher levels of abdominal visceral fat compared to those with lower; 2) if MSNA would be similar in subcutaneous obese men compared with normal weight peers with similar levels of abdominal visceral fat; and 3) if MSNA would be reduced in men with elevated abdominal visceral fat after weight loss. To accomplish these aims, body composition was measured by dual energy x-ray absorptiometry, abdominal fat distribution was measured by computed tomography, and post-ganglionic multi-unit MSNA was measured via microneurography in 18-40 year old sedentary non-obese and obese men. The main findings from these studies were as follows. First, MSNA was elevated in men with higher abdominal visceral fat compared with their age- and total fat mass-matched peers with lower levels (32±4 vs. 21±2 bursts/min, P<0.05). Basal MSNA was more closely associated with abdominal visceral fat (r=0.65, P<0.05) than total body (r=0.32, P=0.05) or abdominal subcutaneous fat (r=0.27, P=0.05). In addition, the relation between abdominal visceral fat and MSNA was independent of total fat mass (r=0.61, P<0.05). Second, MSNA did not differ among subcutaneous obese and normal weight men with similar levels of abdominal visceral fat (22.5±2.7 vs. 23.9±2.3 bursts/min, P>0.05). Importantly, abdominal visceral fat was the only significant body composition or abdominal fat distribution-related correlate of MSNA (r=0.48, P<0.05). Finally, reductions in total body and abdominal fat with weight loss, via caloric restriction, were associated with a ~23% reduction in MSNA in men elevated with abdominal visceral fat. The results of these studies suggest that abdominal visceral fat is an important adipose tissue depot linking obesity with sympathetic neural activation in humans. These findings may have important implications for understanding the elevated risk of cardiovascular disease observed in individuals with visceral obesity.