Beta-adrenoceptors in human airway tissue: relationship between functional responsiveness and receptor number

Functional organ bath experiments and radiolabelled ligand binding studies were used to investigate the relationship between beta-adrenoceptor-mediated relaxation and the total number of beta-adrenoceptors in human lung parenchymal tissue and bronchial tissue. Sensitivity to the beta-adrenoceptor agonist isoprenaline (pD2) varied almost 10-fold (pD2 values 6.00 to 6.85) for lung parenchymal preparations and 35-fold for bronchial preparations (pD2 values 6.16 to 7.67) between patients. The total number of [3H] DHA labelled beta-adrenoceptors (Bmax) varied almost 6-fold for lung parenchymal membrane preparations (Bmax 164 to 936 fmol/mg protein) and less than 2-fold for bronchial tissue membrane preparations (Bmax 188 to 342 fmol/mg protein) between patients. Comparison of sensitivity to isoprenaline and beta-adrenoceptor number for lung parenchymal tissue from the same patient demonstrated a negative correlation (r = -0.80 [95% confidence intervals: -0.13, -0.96], 6 d.f., P less than 0.05), suggesting that beta-adrenoceptor-mediated sensitivity of lung parenchymal tissue is inversely related to the number of beta-adrenoceptors. However, there was an absence of correlation between sensitivity to isoprenaline and beta-adrenoceptor number in bronchial tissue from the same patient. Thus, the findings of the present study do not support the possibility of a direct relationship between the beta-adrenoceptor-mediated responsiveness and the beta-adrenoceptor number of human airway preparations.