Classification of β‐adrenoceptors in isolated bronchus of the pig

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Abstract
1 (±)-Isoprenaline (Iso), (−)-adrenaline (Ad), (−)-noradrenaline (NA), the β2-selective adrenoceptor agonist (±)-fenoterol (Fen) and the β1-selective adrenoceptor agonist (±)-RO363 caused concentration-dependent relaxation of preparations of pig bronchus pre-contracted with carbachol 40 ng/ml (0.22 μM). Iso, Ad, NA and Fen caused complete relaxation of carbachol-induced tone, but RO363 caused relaxation equivalent to only 59% of the maximal response to Iso. 2 When relaxation responses to these amines were plotted as a % of their maximal effects, comparison of EC50 values showed that the order of potency was RO363 > Iso > NA > Fen > Ad (14.4:4.6:1:0.4:0.3). 3 pA2 values determined for the β-adrenoceptor antagonists propranolol (non-selective) and atenolol (β1-selective), or the partial agonist salbutamol (β2-selective) using Iso as agonist were 8.3, 7.3 and 4.4 respectively. The pA2 value for atenolol using RO363 as the agonist was 7.6. 4 These results indicate that porcine bronchus contains a homogeneous population of β1-adrenoceptors.

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