The sympathetic nervous system and the metabolic syndrome

Studies performed in the past two decades have unequivocally shown that several of the components of the metabolic syndrome are associated with indirect and direct markers of adrenergic overdrive. This is the case for hypertension and obesity, in which resting tachycardia, elevated plasma norepinephrine values, increased sympathetic nerve traffic, as well as augmented levels of total and regional norepinephrine spillover have been reported. This is also the case for insulin resistance, i.e. a metabolic condition frequently complicating the various components of the pathological condition identified as the 'metabolic syndrome'. After briefly describing the epidemiological and the cardiovascular risk profile of the disease, this paper will examine the behaviour of the sympathetic nervous system in the metabolic syndrome as well as the mechanisms potentially responsible for this neurogenic abnormality. This will be followed by an analysis of the role played by neuroadrenergic factors in disease progression as well as in the pathogenesis of its complications. Finally, the therapeutic implications of these findings will be highlighted.