WHOLE-BODY, ADIPOSE-TISSUE, AND FOREARM NOREPINEPHRINE KINETICS IN LEAN AND OBESE WOMEN

We evaluated whole body and regional (subcutaneous abdominal adipose t issue and forearm) norepinephrine (NE) kinetics in seven lean (body ma ss index 21.3 +/- 0.5 kg/m(2)) and six upper body obese (body mass ind ex 36.4 +/- 0.4 kg/m(2)) women who were matched on fat-free mass. NE k inetics were determined by infusing [H-3]NE and obtaining blood sample s from a radial artery, a deep forearm vein draining mostly skeletal m uscle, and an abdominal vein draining subcutaneous abdominal fat. Mean systemic NE spillover tended to be higher in obese (2.82 +/- 0.49 nmo l/min) than in lean (2.53 +/- 0.40 nmol/min) subjects, but the differe nces were not statistically significant. Adipose tissue and forearm NE spillover rates into plasma were greater in lean (0.91 +/- 0.08 pmol 100 g tissue(-1).min(-1) and 1.01 +/- 0.09 pmol 100 mi tissue(-1).min( -1), respectively) than in obese (0.26 +/- 0.05 pmol.100 g tissue(-1). min(-1) and 0.58 +/- 0.11 pmol 100 mi tissue(-1).min(-1), respectively ) subjects (P < 0.01). These results demonstrate that adipose tissue i s an active site for NE metabolism in humans. Adipose tissue NE spillo ver is considerably lower in obese than in lean women, which may contr ibute to the lower rate of lipolysis per kilogram of fat mass observed in obesity.