title: Cardiac adrenoceptors at low temperature and the adrenoceptor interconversion hypothesis.
abstract: 1 The hypothesis that low temperature converts inotropic beta-adrenoceptors to alpha-adrenoceptors has been tested in isolated heart preparations of the frog and rat. 2 The results do not support the adrenoceptor interconversion hypothesis. In the frog ventricle strip lowering the temperature from 24 degrees C to 14 degrees C did not significantly alter the inotropic potency of the sympathomimetic drugs isoprenaline, adrenaline and phenylephrine and did not reduce the potency of the beta-adrenoceptor blocking drug propranolol as an isoprenaline antagonist. In the isolated left atrium of the rat lowering the temperature from 31 degrees C and 24 degrees C to 17-19 degrees C did not significantly alter the inotropic potency of isoprenaline, noradrenaline and phenylephrine, did not diminish the potency of the beta-adrenoceptor blocking drug propranolol and did not increase the potency of the alpha-adrenoceptor blocking drug phentolamine. 3 Phenylephrine acted on alpha- and beta-adrenoceptors in rat left atrium at 31 degrees C and 24 degrees C, but only on beta-adrenoceptors at 17-19 degrees C.
mesh_terms: D000818:Animals; D001001:Anura; D003080:Cold Temperature; D006321:Heart / Q000294:innervation*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000502:physiology*
chemical_list: D011941:Receptors, Adrenergic; D011433:Propranolol; D007545:Isoproterenol; D009638:Norepinephrine