Acute and chronic treatment with glucocorticosteroids, modifying the beta 2-adrenergic response of the guinea pig trachea.

The effect of beta 2-adrenoceptor agonists on airway smooth muscle relaxation may be subject to desensitization. It could be modified by glucocorticosteroid treatment. An increase in the beta 2 agonist response by glucocorticosteroids in vitro has been described. We studied the effects of acute and chronic treatment with dexamethasone on the relaxation response of tracheal smooth muscle to beta 2 agonists, fenoterol and salbutamol. Fenoterol showed a greater force of relaxation than salbutamol, and both drugs induced desensitization. Acute treatment with dexamethasone reduced desensitization to both beta 2 agonists. Chronic treatment (120 micrograms/kg of dexamethasone for 7 days) reduced the desensitization to fenoterol alone. Dexamethasone (200 micrograms/kg for 7 days) increased relaxation to salbutamol and reduced desensitization to both drugs. The interaction between beta 2 agonists and glucocorticosteroids could be important in the clinical use of both drugs in the treatment of asthma.