Objective: The purpose of this study was to examine the effects of weight loss on sympathetic nervous system responsiveness to glucose ingestion in obese subjects with metabolic syndrome, in whom such responses are reportedly blunted.
Research design and methods: Thirty four subjects, 19 insulin resistant and 15 insulin sensitive and aged 55 +/- 1 years (mean +/- SE) with BMI 31.6 +/- 0.6 kg/m2, who fulfilled the Adult Treatment Panel III criteria for metabolic syndrome participated. Simultaneous measurements of whole-body norepinephrine spillover rate, calf blood flow, and intra-arterial blood pressure were made at times 0, 30, 60, 90, and 120 min postglucose (75 g). The experiment was repeated after a 3-month hypocaloric diet with or without an exercise program.
Results: Body weight decreased by 8.1 +/- 0.9 and 8.4 +/- 1.1 kg and resting norepinephrine spillover by 94 +/- 31 and 166 +/- 58 ng/min (all P < or = 0.01) in insulin-resistant and insulin-sensitive subjects, respectively. Weight loss was accompanied by a marked increase in sympathetic responsiveness after glucose but only in insulin-resistant subjects. In this subgroup, comparative increases in norepinephrine spillover rates at baseline and after weight loss averaged -3 +/- 25 versus 73 +/- 24 ng/min at 30 min (P = 0.039), 36 +/- 21 versus 115 +/- 28 ng/min at 60 min (P = 0.045), 9 +/- 21 versus 179 +/- 50 ng/min at 90 min (P < 0.001), and 40 +/- 48 versus 106 +/- 39 ng/min at 120 min (P = 0.24).
Conclusions: Weight loss reverses blunted sympathetic responsiveness to glucose ingestion in insulin-resistant subjects with metabolic syndrome, which is relevant to postprandial energy utilization and body weight homeostasis.