BODY-WEIGHT REDUCTION, SYMPATHETIC-NERVE TRAFFIC, AND ARTERIAL BAROREFLEX IN OBESE NORMOTENSIVE HUMANS

Background-Previous studies have shown that sympathetic cardiovascular outflow is increased in obese normotensive subjects and that this inc rease is associated with a baroreflex impairment. The purpose of this study was to determine whether these abnormalities are irreversible or can be favorably affected by body weight reduction. Methods and Resul ts-In 20 obese normotensive subjects (age, 31.3+/-1.7 years; body mass index, 37.6+/-0.9 kg/m(2), mean+/-SEM), we measured beat-to-beat arte rial blood pressure (Finapres technique), heart rate (ECG), postgangli onic muscle sympathetic nerve activity (microneurography at a peroneal nerve), and venous plasma norepinephrine (high-performance liquid chr omatography) at rest and during baroreceptor stimulation and deactivat ion induced by increases and reductions of blood pressure via stepwise intravenous infusions of phenylephrine and nitroprusside. Measurement s were repeated in 10 subjects after a 16-week hypocaloric diet with n ormal sodium content (4600 to 5000 J and 210 mmol NaCl/d) and in the r emaining 10 subjects after a 16-week observation period without any re duction in the caloric intake. The hypocaloric diet significantly redu ced body mass index, slightly reduced blood pressure, and caused a sig nificant and marked decrease in both muscle sympathetic nerve activity (from 50.0+/-5.1 to 32.9+/-4.6 bursts per 100 heart beats, P<.01) and plasma norepinephrine (from 356.2+/-43 to 258.4+/-29 pg/mL, P<.05). T his was associated with a significant improvement in the sensitivity o f the baroreceptor heart rate (+71.5+/-11%, P<.01) and muscle sympathe tic nerve activity (+124.5+/-22%, P<.001) reflex. Total body glucose u ptake also increased significantly (+60.8+/-12.0%, P<.05), indicating an increase in insulin sensitivity. All variables remained unchanged i n subjects not undergoing caloric restriction. Conclusions-In obese no rmotensive subjects, a reduction in body weight induced by a hypocalor ic diet with normal sodium content exerts a marked reduction in sympat hetic activity owing to central sympathoinhibition. This can be due to the consequences of an increased insulin sensitivity but also to a re storation of the baroreflex control of the cardiovascular system with weight loss.