Effects of physical training on adrenergic sensitivity in obesity

To examine the possibility that the decrease of hyperinsulinemia and blood pressure in obesity associated with physical training is mediated via adaptations in the adrenergic nervous system, a pure beta-adrenergic agonist (isoproterenol) or an alpha-adrenergic antagonist (phentolamine) was infused before and during an oral glucose tolerance test before and after physical training. A number of circulatory, metabolic, and endocrine factors under adrenergic control were followed. Physical training was associated with an augmented beta-agonist response in blood pressure, heart rate, blood glucose, plasma insulin, connecting (C) peptide, and pancreatic polypeptide (PP) but not in plasma glucagon and gastric inhibitory polypeptide. Physical training also resulted in higher values of C-peptide and PP values after alpha-adrenergic blockade. It was concluded that physical training probably is associated with an augmented sensitivity of the beta-adrenergic nervous system. This might also be the case with the alpha-adrenergic system. It was suggested that this in turn might be due to a decreased firing in the adrenergic nervous system leading secondarily to an increased sensitivity in the effector cells. It was hypothesized that such decreased firing could provide a background to explain lower blood pressure and plasma insulin after physical training.