beta-adrenoceptor reserve in human lung: a comparison between airway smooth muscle and mast cells

The effects of several beta-adrenoceptor agonists on the relaxation of prec ontracted human bronchial rings and the inhibition of IgE-mediated histamin e release from human lung mast cells (HLMC) were studied. For the relaxatio n of bronchial rings, isoprenaline, fenoterol and terbutaline were full ago nists whereas salbutamol was a full agonist in some (two out of six) experi ments and a partial agonist in the remainder. For the inhibition of histami ne release, relative to isoprenaline, neither fenoterol, terbutaline nor sa lbutamol was a full agonist. Studies with the irreversible beta-adrenocepto r antagonist, bromoacetylalprenolol menthane, indicated that there was a la rger beta-adrenoceptor reserve for the relaxation of precontracted bronchia l rings than for the inhibition of histamine release from HLMC. Further stu dies indicated that the isoprenaline inhibition of histamine release was co nsiderably more susceptible to desensitizing treatments than the isoprenali ne relaxation of bronchial rings. Collectively, these data suggest that a l arger beta-adrenoceptor reserve exists for the relaxation of smooth muscle than the inhibition of histamine release from HLMC and that differences in receptor reserve may contribute to the relative susceptibilities of the two systems to desensitization. (C) 1999 Elsevier Science B.V. All rights rese rved.