Long- and short-acting β2 adrenoceptor agonists: Interactions in human contracted bronchi

Abstract

The aim of this study was to systematically compare the interaction of the long-acting β2-adrenoceptor agonists formoterol and salmeterol with short-acting β2-adrenoceptor agonists in contracted human bronchi. Human bronchi were obtained at thoracotomy from patients with lung cancer. Formoterol or salmeterol at concentrations inducing up to 92 and 94% of their maximal relaxant effect, respectively, were added to bronchial rings contracted with carbachol (10-6 M). After a time period of 30 min, concentration-response curves for the short-acting β2-adrenoceptor agonists, salbutamol, terbutaline, isoprenaline and fenoterol were recorded. Administration of equieffective concentrations of salmeterol and formoterol, resulted in only salmeterol inducing a shift to the right of isoprenaline, terbutaline, fenoterol and salbutamol concentration-response curves. The rank order of shift was salbutamol > fenoterol > terbutaline > isoprenaline. Formoterol, up to concentrations of 3x10-9 M induced submaximal relaxation resulting in no shift in short-acting β2-adrenoceptor agonist concentration-response curves. Salmeterol but not formoterol appears to antagonize the relaxation of human contracted bronchi induced by short- acting β2-agonists. These results obtained in vitro cannot be translated in clinical terms. This study, however, highlights the need for clinical studies on the interaction of long-acting and short-acting β2-adrenoceptor agonists in acute severe asthma.