Inhibitory effects of terbutaline on human esophageal peristalsis and development of tolerance

To investigate the inhibitory influence on esophageal motility of prolonged beta-2-adrenergic stimulation, esophageal peristalsis was studied in 10 volunteers. The beta-2 agonist terbutaline was given orally, 5 mg three times daily, for 10 days, and the subjects were studied before medication (basal), on days 3 and 10 during the medication, and 1 week after withdrawal of the drug. At each session esophageal peristaltic pressure, heart rate, and finger tremor were assessed. On the 3rd day of medication the peristaltic pressure was significantly decreased and heart rate and finger tremor significantly increased compared with basal values on day 0. On the 10th day of medication there was still a decrease in peristaltic pressure but less pronounced than on day 3 despite similar blood levels of terbutaline. It is concluded that oral medication with a beta-2 agonist initially inhibits esophageal peristalsis, but during continued medication the inhibitory effect on the esophagus decreases. The results indicate development of esophageal tolerance to beta-2-receptor stimulation in accordance with development of tolerance shown in extraintestinal organs.