SYMPATHETIC NERVOUS-SYSTEM ACTIVITY, BODY FATNESS, AND BODY-FAT DISTRIBUTION IN YOUNGER AND OLDER MALES

It was hypothesized that an increase in total and central body fatness is related to higher sympathetic nervous system activity (SNSA) in ol der men. Resting SNSA was measured from norepinephrine (NE) kinetics i n 69 younger (18-36 yr) and 69 healthy older men (55-80 yr). Body fat distribution was estimated from the waist circumference, body composit ion from underwater weighing, peak oxygen consumption from a treadmill test to exhaustion, and dietary intake from food diaries. Plasma NE c oncentrations were 41% higher (P < 0.001) in older men due to a 27% in crease (P < 0.001) in NE appearance rate and a tendency for a lower NE clearance rate (P = 0.08). NE appearance rate was higher in individua ls of both age groups who exhibited a greater waist circumference and body fatness (range of r values 0.49-0.69; P < 0.01). The waist circum ference, and not-age, was the strongest predictor of the increase in N E appearance rate in older men. Statistically controlling for the wais t circumference or body fatness diminished age-related differences in NE concentrations and in NE appearance rate. These findings suggest th at an accumulation of total and central body fat is associated with hi gher levels of SNSA in older males.