Treatment with high doses of terbutaline induces beta-adrenergic desensitization of guinea pig trachea not prevented by the addition of dexamethasone.

BACKGROUND

The combination of beta(2)-adrenergic agonists and glucocorticosteroids is frequently used to control bronchial asthma. It is believed that the co-administration of glucocorticosteroids will reduce the tachyphylaxis to beta(2)-adrenergic agonists.

OBJECTIVE

To analyse the effects of glucocorticosteroids on the response to high concentrations of beta(2)-adrenergic agonists.

METHODS

We have compared the effects of high doses of terbutaline, alone or in combination with dexamethasone, on the relaxation induced by in vitro beta(2)-adrenergic agonists in guinea pig trachea.

RESULTS

Terbutaline (100 mg/kg/day), for 7 days, induced a marked homologous desensitization. The addition of dexamethasone (0. 2 or 2 mg/kg/day) to the treatment did not prevent the development of desensitization, which was even more marked in the group treated with terbutaline and the higher doses of dexamethasone, compared with the group treated with terbutaline alone.

CONCLUSION

Our results suggest a negative interaction between high doses of beta(2)-adrenergic agonists and glucocorticosteroids in the airway smooth muscle of guinea pigs.