title: Effect of hypothermia on beta 1-adrenoceptor-mediated relaxation of pig bronchus.
abstract: The relaxant potencies of (+/-)-isoprenaline and of (-)-noradrenaline (NA) in the pig isolated bronchus were increased 5.4 and 3.1 fold respectively by lowering the organ bath temperature from 37 degrees C to 27 degrees C, whereas the potencies of the non-catecholamine beta-adrenoceptor agonists fenoterol and orciprenaline were not significantly changed. At 37 degrees C, the catechol-O-methyl transferase (COMT) inhibitor U-0521 (30 microM), caused a 7.2 fold increase in the potency of isoprenaline but had no effect on the potency of fenoterol. At 27 degrees C the potency of isoprenaline was similar in the absence or presence of U-0521 (30 microM). Furthermore, in bronchi where extraneuronal uptake was inhibited by phenoxybenzamine, the potency of NA was not significantly altered by reducing bathing temperature from 37 degrees C to 27 degrees C. These results suggest that the hypothermic potentiation of isoprenaline in pig bronchus resulted from inhibition of COMT or of access to COMT, rather than from sensitization of beta 1-adrenoceptors.
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000403:Airway Resistance / Q000187:drug effects*; D000818:Animals; D001980:Bronchi / Q000187:drug effects; D065098:Catechol O-Methyltransferase Inhibitors; D003080:Cold Temperature; D004347:Drug Interactions; D006854:Hydrocortisone / Q000494:pharmacology; D066298:In Vitro Techniques; D011427:Propiophenones / Q000494:pharmacology; D013552:Swine
chemical_list: D000318:Adrenergic beta-Agonists; D065098:Catechol O-Methyltransferase Inhibitors; D011427:Propiophenones; C006104:U 0521; D006854:Hydrocortisone