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β 1 ‐Adrenoceptors mediate smooth muscle relaxation in mouse isolated trachea
Author(s) -
Henry Peter J.,
Goldie Roy G.
Publication year - 1990
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.1476-5381.1990.tb14666.x
Subject(s) - isoprenaline , agonist , fenoterol , endocrinology , medicine , carbachol , methoxamine , chemistry , atenolol , schild regression , partial agonist , intrinsic activity , adrenergic receptor , betaxolol , biology , receptor , stimulation , asthma , blood pressure , timolol , neuroscience , glaucoma
1 The relaxant effects to the β‐adrenoceptor agonists isoprenaline, adrenaline, noradrenaline, RO363, procaterol and fenoterol were investigated in carbachol‐contracted mouse isolated tracheal preparations. 2 The order of potencies for those β‐adrenoceptor agonists that induced full relaxation of carbachol‐contracted mouse tracheal preparations was isoprenaline > RO363 > noradrenaline = adrenaline > fenoterol. The EC 50 value of isoprenaline for relaxation was 46 n m . The β 1 ‐adrenoceptor‐selective agonist, RO363, was ten times more potent than the β 2 ‐adrenoceptor‐selective agonist, fenoterol. The highly β 2 ‐adrenoceptor‐selective agonist procaterol was a partial relaxant and induced only 28 ± 4% relaxation. 3 Relaxations induced by noradrenaline and isoprenaline were not significantly affected by the neuronal uptake inhibitor, cocaine (10 μ m ) or by the extraneuronal uptake inhibitor, deoxycorticosterone acetate (25 μ m ) respectively. The α‐adrenoceptor agonist methoxamine induced no observable elevation of mouse tracheal smooth muscle tone. 4 Schild plots for the β‐adrenoceptor antagonists, atenolol and betaxolol (β 1 ‐adrenoceptor‐selective) and ICI 118,551 (β 2 ‐adrenoceptor‐selective) were linear, with slope values approaching unity. Mean pA 2 values derived for atenolol, betaxolol and ICI 118,551 for antagonism of β‐adrenoceptor‐mediated relaxation were 7.1, 8.4 and 7.2, respectively. These data were independent of the use of isoprenaline or noradrenaline as the agonist. 5 These findings indicate that β‐adrenoceptor‐mediated relaxations of mouse isolated trachea occur predominantly through activation of β 1 ‐adrenoceptors.