Temperature-dependent supersensitivity of isolated atria to catecholamines

Experiments with isolated guinea-pig atria show that lowering of temperature from 37 to 27°C induced supersensitivity to noradrenaline, isoprenaline, dopamine and orciprenaline which was not due to impairment of the uptake mechanisms (neuronal or extraneuronal) or to impairment of enzyme activity (catechol-O-methyl transferase or monoamine oxidase). While the reason for the supersensitivity remains to be analysed in detail, the results are inconsistent with the postulate of Muñoz-Ramíres et al. (1973) that an impairment of the activity of catechol-O-methyl transferase is responsible for hypothermia-induced supersensitivity to catecholamines.