Heart rate and plasma cyclic AMP responses to isoproterenol infusion and effect of beta-adrenergic blockade in patients with postural orthostatic tachycardia syndrome

To clarify the pathophysiological mechanism of postural orthostatic tachyca rdia syndrome (POTS), the responses of heart rate and the plasma cyclic AMP (cAMP) level to isoproterenol infusion in the supine position were evaluat ed in 10 POTS patients and 10 age-matched controls. Also, the effect of bet a-adrenegic blockade on POTS was assessed using the head-up tilt test. The POTS patients consisted of two men and eight women, with a mean age of 19.7 years (range, 15-28 years). An exaggerated increase of both heart rate and the plasma cAMP concentration after isoproterenol infusion at a low dose ( 1 mug/min) was observed in the POTS patients, but not in control subjects. Seven POTS patients received oral beta-blocker therapy. In five of these, s ymptoms were abolished and there was a smaller heart rate increase during t he head-up tilt test. These data suggest that POTS may be more prevalent in young women and that beta-adrenergic hypersensitivity may play a role in t he mechanisms of this syndrome. However, a larger series of patients need t o be studied in the future.