Influence of temperature on the sensitivity of the adrenoceptors in the isolated atria of guinea pigs and rats.

The influence of the bath temperature on the responsiveness to sympathomimetic amines was studied with isolated guinea pig and rat atria. In electrically driven guinea pig left atria, the dose-response curve for the positive inotropic effect of isoproterenol (ISO) was shifted to the left by lowering the temperature from 36 to 24 degrees C. The positive inotropic effect of phenylephrine (PHE) in lower concentrations was attenuated by lowering the temperature. Phentolamine markedly inhibited the PHE response at 36 and 32 degrees C, whereas it produced no inhibition at 24 degrees C. Similar changes were observed with rat left atria. In guinea pig left atria, propranolol inhibited the response to PHE more effectively at 24 degrees C than 32 degrees C. With guinea pig and rat atria the dose--response curve for the positive inotropic effect of PHE in the presence of phentolamine was shifted to the left by lowering the temperature. The results suggest that lowering the temperature of the bath solution diminished the positive inotropic effect of PHE mediated by alpha-adrenoceptors and potentiated that mediated by beta-adrenoceptors.