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β‐Adrenoceptor heterogeneity in guinea‐pig airways: comparison of functional and receptor labelling studies
Author(s) -
Carswell Heather,
Nahorski Stefan R.
Publication year - 1983
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1983.tb10542.x
Subject(s) - guinea pig , agonist , antagonist , isoprenaline , dihydroalprenolol , radioligand , atenolol , endocrinology , medicine , chemistry , receptor , clenbuterol , schild regression , adrenergic receptor , partial agonist , biology , biophysics , stimulation , blood pressure
1 The distribution of β‐adrenoceptor subtypes in guinea‐pig airways has been studied by radioligand binding assays and analysis of mechanical responses. 2 Binding studies with the ligands [ 3 H]‐dihydroalprenolol and [ 125 I]‐cyanopindolol, revealed that β‐adrenoceptors were unevenly distributed throughout the airways with the highest density located in the parenchyma and the lowest density in the trachea. 3 The relative proportion of β 1 :β 2 ‐adrenoceptor binding sites was assessed by computer‐assisted analysis of the inhibition curves generated by selective agents. It was virtually identical in each region and in the order of 15:85%. 4 β‐Adrenoceptor agonists caused concentration‐dependent relaxations of both tracheal spirals and parenchymal lung strips. This response appeared to be mediated by both β 1 ‐ and β 2 ‐adrenoceptors in tracheal spirals as the pA 2 value for the β 1 ‐selective antagonist, atenolol, varied depending upon which agonist was used, and, in the presence of the β 2 ‐adrenoceptor antagonist ICI 118,551, noradrenaline and isoprenaline produced biphasic concentration‐effect curves. In parenchymal lung strips only the one subtype was involved as antagonist pA 2 values were not dependent on the agonist used and the properties were consistent with those expected for a β 2 ‐adrenoceptor.