Effect of beta-adrenergic blockade on circulating catecholamines and dopamine-beta-hydroxylase activity during...

We investigated the effects of beta-adrenergic blockade with propranolol (P) on circulating catecholamines at rest and during isometric and dynamic exercise. By means of a radioenzymatic assay, we measured plasma norepinephrine (NE) and epinephrine (E) concentrations in nine normal, sedentary men, aged 22 to 34 years. Measurements were made during resting conditions, at 3 minutes of 30% maximal isometric handgrip exercise (IHE), and during submaximal and maximal dynamic treadmill exercise. Measurements were repeated one week later after the subjects received P in doses ranging from 40 to 80 mg four times a day (plasma P levels at the time of exercise ranged from 96 to 303 ng/ml with a mean of 178 ng/ml). We also measured serum dopamine-beta-hydroxylase (DBH) activity to detect changes in chronic sympathetic tone. Changes in NE from rest to exercise were significant (p less than 0.01) at all exercise loads with or without P. Changes in E from rest to exercise were significant (p less than 0.01) at all exercise loads with or without P except for submaximal dynamic exercise during the control study (p greater than 0.05). For NE, there were no significant differences between the control and P values either at rest or during any form of exercise. For E, there were no significant changes between the control and p values at rest or at maximal dynamic exercise, although there were mild increases (p less than 0.05) with IHE and submaximal dynamic exercise. DBH activity increased significantly (p less than 0.01) from rest to exercise for all exercise points with and without P, but there were no significant differences between the control and p values either at rest or during any form of exercise. In conclusion, we have demonstrated that competitive blockade of beta-adrenergic receptors at the tissue level does not alter neural release of NE or DBH and has little effect on adrenal release of E.