title: Classification of postjunctional beta adrenoceptors mediating relaxation of canine bronchi.
abstract: Adrenoceptors mediating relaxant responses to exogenously added or endogenously released catecholamines in isolated canine bronchi (3rd-6th order) were characterized using selective beta receptor agonists and antagonists. Norepinephrine (3 x 10(7) to 3 x 10(-5) M) or isoproterenol (3 x 10(-8) to 10(-6) M) fully relaxed tissues precontracted with 3 x 10(-7) M carbachol (Cch). Salbutamol (Sal) also relaxed Cch-precontracted tissues, but this relaxant effect was extremely sensitive to the concentration of precontracting agent used: the maximal effect of Sal was 100, 79 and 28% reversal of tone in tissues precontracted with 2 x 10(-8), 10(-7) and 3 x 10(-7) M Cch. The effects of isoproterenol were antagonized by propranolol. Norepinephrine relaxations were antagonized by the beta-1-selective antagonist ICI 89,406 (pA2 = 7.70) and the beta-2-selective antagonist ICI 118,551 (pA2 = 6.33). Sal-relaxations were antagonized by ICI 118,551 (pA2 = 8.91). Field stimulation in tissues precontracted with McNeil A343 (M1-selective muscarinic agonist) produced transient relaxations which were antagonized by ICI 89,406 but not ICI 118,551 (both 10(-9) to 10(-7) M). Thus, exogenous and endogenous catecholamines relax canine bronchial smooth muscle by activating both beta-1 and beta-2 adrenoceptors, although the latter seen to play a significant role only when low concentrations of Cch were used.
authors.affiliation: Department of Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
authors.forename: L J
authors.initials: LJ
authors.lastname: Janssen
authors.forename: E E
authors.initials: EE
authors.lastname: Daniel
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000420:Albuterol / Q000494:pharmacology; D000818:Animals; D001980:Bronchi / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D004285:Dogs; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000145:classification* / Q000502:physiology
chemical_list: D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D002217:Carbachol; D000420:Albuterol; D002118:Calcium; D009638:Norepinephrine