The relationship of muscle sympathetic nerve activity to the sympathetically‐mediated thermic effect of food in young healthy subjects

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The thermic effect of food (TEF) is partially mediated by β‐adrenergic receptors (βAR) and is an important component of daily energy expenditure. Greater sympathetic activity has been associated with decreased BAR responsiveness. We hypothesized that muscle sympathetic nerve activity (MSNA) would be inversely correlated with the βAR component of TEF (TEFβ). We measured MSNA (microneurography) and energy expenditure (EE) (indirect calorimetry) before and for 5 h after a mixed meal (40% daily EE). Measurements were made during systemic βAR blockade with propranolol (BB) and saline (NS) infusion on separate days in 10 healthy subjects (2 female, age 28±2 y, BMI 24.4±0.6 kg/m2). Resting MSNA was 39±3 bursts/100 heartbeats (hb). Within 1 h after the meal, MSNA significantly increased during both NS (12±3 bursts/100 hb) and BB (18±4) but was not significantly different between the two days, (P=0.375). The maximum increase in REE after the meal was 269±29 (NS) and 198±22 (BB) kcal/24 h (P<0.05). TEFβ (TEFβ = AUC TEFNS – AUC TEFBB) was 48±20% of total TEF. TEFβ was positively correlated with resting MSNA (R2=0.70, P<0.05). Contrary to our hypothesis, we found that greater levels of MSNA were associated with greater TEFβ. These results indicated that resting MSNA may be an important contributor to daily energy expenditure. Studies are needed to determine if greater MSNA is associated with a resistance to weight gain.The project described was supported by the Mayo Foundation for Medical Education and Research and NIH Grant Numbers K23 DK82424, P30 DK50456, and UL1 RR024150.