Failure of chronic beta-adrenergic blockade to inhibit overfeeding-induced thermogenesis in humans.

The effect of the beta-adrenergic antagonist propranolol on the increase in resting metabolic rate (RMR) induced by overfeeding was examined to determine whether increased beta-adrenergic activity contributes to this response. Six male subjects who were overfed with carbohydrate (1,600 excess kcal/day) for 10 days without drug treatment (control group) had increases (compared with values after 10 days of weight maintenance) in RMR after 6 days [0.24 +/- 0.06 kcal/min (22%)] and 10 days of overfeeding [0.17 +/- 0.03 kcal/min (15%)]. Eight male subjects were given a weight-maintenance diet for 10 days with oral propranolol treatment (40-60 mg every 6 h) over the last 7 days of this period. Five of these subjects were then overfed for 10 days, and three remained on the weight-maintenance diet; propranolol treatment continued until the end of the study. Propranolol significantly reduced RMR (mean 9%) before the onset of overfeeding but did not prevent increases in RMR after 6 days [0.18 +/- 0.05 kcal/min (16%)] and 10 days of overfeeding [0.17 +/- 0.03 kcal/min (15%)]. In the subjects who remained on the weight-maintenance diet throughout the study, there was no reversal of propranolol's initial reduction of RMR that would have falsely elevated the overfeeding effect. These data provide further evidence that the increase in RMR induced by overfeeding in humans is not mediated by increased beta-adrenergic activity.