Effect of short- and long-acting beta(2)-adrenoceptor agonists on pulmonary beta(2)-adrenoceptor expression in human lung

beta-Adrenoceptor agonists induce the down-regulation of beta(2)-adrenoceptors and mRNA expression in animal lung. The down-regulation of beta(2)-adrenoceptors may limit the therapeutic efficacy of beta(2)-adrenoceptor-mediated bronchodilators in obstructive airways disease. We examined the effects of three selective beta(2)-adrenoceptor agonists, salbutamol, salmeterol and formoterol on beta(2)-adrenoceptor binding and mRNA levels in human lung in vitro. Human lung was obtained from cardiac transplantation donors. Peripheral lung was chopped and incubated with three selective beta(2)-adrenoceptor agonist for 3 h or 24 h at three different concentrations (0.1, 1 and 10 mu M). The affinity and density of beta(2)-adrenoceptors was determined by [I-125]iodocyanopindolol equilibrium binding in a lung membrane preparation in the presence of 0.1 mu M CGP 20712 A (1-{2-[(3-carbamoyl-4-hydroxy)phenoxy]ethylamino}-3-[4-(1-methyl-4-trifluoromethyl-2-imidazolyl)phenoxy]-propan-2-ol), a selective beta(1)-adrenoceptor antagonist. Although treatment with salbutamol for 3 h did not change beta(2)-adrenoceptor density, both salmeterol and formoterol reduced beta(2)-adrenoceptor density, and exposure to each agonist for 24 h reduced beta>(2)-adrenoceptor density at all concentrations. Treatment with 10 mu M salmeterol increased the eqilibrium dissociation constant (K-d), and also shifted the competition curves of (-)-isoprenaline to the left. beta(2)-Adrenoceptor mRNA, measured by Northern blot analysis using a human beta(2)-adrenoceptor cDNA probe, was reduced after exposure to all beta(2)-adrenoceptor agonists at 3 h. Our data provide evidence for down-regulation of beta(2)-adrenoceptor protein and mRNA after selective beta(2)-adrenoceptor agonist treatment in human lung.