Sympathetic activation in obese normotensive subjects

Human obesity is characterized by profound alterations in the hemodynamic and metabolic states. Whether these alterations involve sympathetic drive is controversial. In 10 young obese subjects (body mass index, 40.5±1.2 kg/m², mean±SEM) with normal blood pressure and 8 age-matched lean normotensive control subjects, we measured beat-to-beat arterial blood pressure (Finapres technique), heart rate (electrocardiogram), postganglionic muscle sympathetic nerve activity (microneurography at the peroneal nerve), and venous plasma norepinephrine (high-performance liquid chromatography). The measurements were performed in baseline conditions and, with the exception of plasma norepinephrine, during baroreceptor stimulation and deactivation caused by increases and reductions of blood pressure via intravenous infusions of phenylephrine and nitroprusside. Baseline blood pressure and heart rate were similar in obese and control subjects. Plasma norepinephrine was also similar in the two groups. Muscle sympathetic nerve activity, however, was 38.6±5.1 bursts per minute in obese subjects and less than half that level in control subjects (18.7±1.3 bursts per minute), the difference being highly statistically significant (P