Advances in our understanding of the role of the sympathetic nervous system in obesity.

The sympathetic nervous system (SNS) and adrenal medulla are important regulators of many physiological processes, not only concerned with the control of blood pressure, but also of metabolism. It is important to realise that activation of the SNS and adrenal medulla usually occurs selectively, rather than in an all or none manner, and that in some circumstances there can be activation of some tissues/organs and suppression of the SNS supply to others. There is evidence that the SNS affects energy expenditure, with studies in both animals and humans pointing to activation of beta-adrenoceptors as being of major importance. Thus, any alteration in the activity or effectiveness of the SNS or adrenal medulla could affect resting energy expenditure and influence the development of obesity. This review assesses the techniques available for evaluating SNS activity and considers the evidence that SNS activity is reduced in obesity. The possibility that defective SNS stimulation of energy expenditure could be altered pharmacologically is considered, and the conclusion drawn that any such approach must produce compounds which are selective for effects on metabolism, and do not cause generalized activation of the SNS.