A COMPARISON OF THE THERMOGENIC, METABOLIC AND HEMODYNAMIC-RESPONSES TO INFUSED ADRENALINE IN LEAN AND OBESE SUBJECTS

The objective of this work was to study adrenoceptor sensitivity in vi vo in a number of tissues in lean and obese humans. The thermogenic, m etabolic and cardiovascular responses to a 90 min infusion of adrenali ne were measured. The subjects were eleven obese subjects (Body Mass I ndex 36.0 +/- 1.2 kg/m(2)) and 10 non-obese subjects (Body Mass Index 21.9 +/- 0.7 kg/m(2)). Metabolic rate, heart rate, blood pressure, for earm blood flow, plasma palmitate turnover and oxidation were measured . Thermogenic responses to adrenaline were similar in the lean and obe se groups (14.4 +/- 1.6 and 15.1 +/- 1.6 J/min/kg fat free mass respec tively). Of the cardiovascular variables measured, only the increase i n forearm blood flow during adrenaline infusion differed between lean and obese, being 3.9 +/- 0.5 and 1.9 +/- 0.3 ml/min/l00 ml forearm res pectively. Basal plasma palmitate turnover rates were lower in the obe se when expressed per unit fat mass (2.32 +/- 0.17 and 7.61 +/- 1.20 m u mol/min/kg fat mass respectively). Basal plasma palmitate oxidation rates were higher in the obese when expressed per unit fat free mass ( 1.53 +/- 0.19 and 0.82 +/- 0.12 mu mol/min/kg fat free mass respective ly). In response to adrenaline palmitate turnover increased similarly in both groups, but plasma palmitate oxidation rates fell in the obese whilst they were unchanged in the lean. In the basal state the obese do not appear to have a defect in fat oxidation, but their response to infused adrenaline may favour fat storage over oxidation. No thermoge nic defect was shown in the obese.