Miles, John M.

The physiological changes that occur after gastric bypass surgery (GBS) are not well understood but changes in activation of the sympathetic nervous system may be involved. We hypothesized that GBS would be associated with greater sympathetically mediated resting energy expenditure as measured by a greater decrease in REE after beta‐blockade (beta‐REE). Subjects who had undergone GBS (average reduction in BMI of 31.6% from peak, N=7) along with lean (BMI<25 kg/m 2 , N=5) and obese (BMI=35–45 kg/m 2 , N=4) subjects underwent measurements of REE before and after IV propranolol (0.25 mg/kg bolus followed by an infusion of 0.004 mg/kg/min). The decrease in REE (mean±SD) after beta‐blockade tended to be greater in lean (102±58 kcal) compared with obese (−22±100 kcal) and GBS (26±55 kcal) subjects (P=0.06). The decrease in REE after beta‐blockade negatively correlated with the % body fat (r=0.54, P<0.05) and VO 2max (r=0.67, P=0.01) of the subjects, but not with resting catecholamine or leptin levels. We did not find that subjects who had undergone GBS had a significant difference in the amount of their REE that is dependent on sympathetic stimulation. Beta‐REE appears to be related to fitness and also to fatness and the fact that GBS subjects had high body fat even after significant weight loss may explain our results. Support: NIH HL46493, NIH CTSA UL1‐RR24150, Department of Anesthesiology.