Adrenomedullary function and its regulation in obesity

Sympathoadrenal system (SAS) represents a major contributor to body homeostasis, regulating blood pressure heart rate, energy balance and intermediary metabolism. Thus, it is not unexpected that in last decades a consistent literature has been focused on the possible role of sympathoadrenal system in the pathogenesis of human obesity. There are, however, many factors confounding comparison of sympathoadrenal system activity between lean and obese subjects. Among these, one should be aware that SAS should be functionally separated into sympathetic nervous system (SNS) and adrenal medulla (AM), and that each of these two systems can be activated independently from the other by distinct physiological stimuli; this phenomenon in fact underlies the discordant pattern of findings for adrenomedullary and sympathetic activity in human obesity. While, in fact, obese subjects often display an increased basal SNS activity, there are numerous reports of blunted AM function in obese. Recent evidence suggests that this reduced adrenaline secretion is an acquired feature of human obesity, a finding that fits in well with the hypothesis that hormonal mileu, particularly sex steroids and cortisol, plays a role in the determination of blunted AM activity. Catecholamines have been recently demonstrated to play a role also in the regulation of whole energy balance. Adrenaline in fact acutely reduces both leptin mRNA as well as circulating leptin in human obese subjects, suggesting that catecholamines may influence the cross-talk between energy stores and the centrally mediated modulation of food intake. In summary, the study of adrenomedullary function and of possible mechanisms of its disturbances in human obesity, appears of great interest, and surely deserves further investigations.