β2-Adrenoceptor desensitization in human alveolar macrophages induced by inhaled terbutaline in vivo is not counteracted by budesonide

In vitro studies suggest that glucocorticoids may counteract β-agonist-induced desensitization of β-adrenoceptors by actions at the transcriptional level, but the clinical relevance of such findings is not clear. Oral terbutaline treatment decreases β-adrenoceptor sensitivity in alveolar macrophages in vivo. This effect is not counteracted by inhaled or orally taken steroids. We therefore examined whether inhaled terbutaline elicited a similar effect on β₂-adrenoceptor sensitivity in alveolar macrophages, and if co-treatment with an inhaled steroid, budesonide, would prevent such down-regulation. Bronchoalveolar lavage (BAL) and lung function tests, including bronchodilator responses to inhaled terbutaline, were performed before and after 2 weeks of regular inhalation of terbutaline, 0.5 mg three times daily, and budesonide, 400 µg twice daily, or placebo, in 24 healthy volunteers. Four untreated subjects served as controls. A marked, approx. 90%, decrease in isoprenaline-induced cAMP accumulation in alveolar macrophages was found in both treatment groups after 2 weeks, with no difference between placebo and budesonide (P = 0.45). In the untreated control group, cAMP responses to both isoprenaline and prostaglandin E₁ tended to be lower on the second occasion. A limited, non-specific desensitization of adenylate cyclase activity thus contributed to the marked desensitization elicited by terbutaline inhalations. The bronchodilator response to inhaled terbutaline did not change after treatment in any of the three groups (F = 0.9, P = 0.50). In conclusion, inhalation of a β-agonist induced marked down-regulation of β₂-adrenoceptor sensitivity in alveolar macrophages in vivo without influencing the bronchodilator response to a β₂-agonist in healthy subjects. Co-treatment with an inhaled steroid failed to counteract the desensitization of alveolar macrophage β₂-adrenoceptors.