Downgrading of biochemical and cardiovascular responses to an intravenous infusion of terbutaline following chronic treatment with oral terbutaline.

Beta 2-agonists are known to cause a range of unwanted biochemical and cardiovascular responses. The present study was designed to investigate the effect of chronic exposure to beta 2-stimulation on the magnitude of these responses produced by an acute challenge with a beta 2-agonist. In this single blind placebo controlled study in six healthy male volunteers, we have compared the effects of chronic dosing with either oral terbutaline (5 mg three times daily for two weeks) or placebo on a number of these responses produced by an intravenous infusion of terbutaline (6 micrograms per kilogram over 1 hour). The infusion was given twenty-four hours after the last dose of oral terbutaline or placebo. The rise in pulse rate, systolic blood pressure and plasma glucose and the fall in serum potassium during terbutaline infusion, although still demonstrable, were significantly reduced following treatment with oral terbutaline compared to placebo. This suggests downgrading of beta-receptor function after chronic beta 2-stimulation.