Cardiac inotropic beta adrenoceptors are fully active at low temperature.
The purpose of this study was to test the adrenoceptor interconversion hypothesis of Kunos and Nickerson (Brit. J. Pharmacol. 59: 603--614, 1977) which claims that lowering temperature from 31 to 17 degrees C converts inotropic beta adrenoceptors in rat atria to alpha adrenoceptors. If lowering temperature transforms the adrenoceptor from a beta type to an alpha type, one should expect that the sympathomimetic drug phenylephrine would be more potent at the low than at the high temperature, that the reverse would be true for the sympathomimetic drug isoproterenol, and that the blocking ability of the beta adrenoceptor blocking drug propranolol might be reduced and that of the alpha adrenoceptor blocking drug phentolamine increased by lowering temperature. This was not observed. It was impossible to obtain satisfactory inotropic effects at 17 degrees C and the calcium concentration in the incubation medium had to be reduced, which lowered contractility and permitted strong inotropic effects. At 17 degrees C the sympathomimetic drug effects were inhibited only by propranolol and not by phentolamine, and there was no evidence of "adrenoceptor interconversion."
D000818:Animals; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000502:physiology; D013696:Temperature
D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D010656:Phenylephrine; D011433:Propranolol; D007545:Isoproterenol; D009638:Norepinephrine; D010646:Phentolamine