TOLERANCE TO THE INDUCTION OF CARDIAC ARRHYTHMIAS BY ADRENALINE IN CYCLOPROPANE-ANAESTHETIZED DOGS

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Abstract
Long-continued maintenance of anaesthesia with cyclopropane has been reported to inhibit the induction of arrhythmias by adrenaline through an "adrenolytic effect". This effect is not observed in dogs in which anaesthesia is maintained with 20% cyclopropane, although a tachyphylaxis to the arrhythmic effect of adrenaline develops with repeated injections of the amine. Tachyphylaxis to the induction of multifocal and fibrillatory ventricular rhythms by adrenaline occurs less readily in the thiopental-treated animal. An "adrenolytic effect", independent of the number of injections of adrenaline, is apparent at higher concentrations of cyclopropane. The latter observation may explain in part the finding that cardiac arrhythmias are demonstrable within a limited range of cyclopropane concentrations.