CORYNANTHINE INHIBITS, WHILE IDAZOXAN POTENTIATES, CARDIOTOXIC EFFECTS OF OUABAIN

1 Ouabain, infused intravenously to anaesthetized guinea-pigs induced ventricular premature beats, ventricular tachyarrhythmias and lethalit y. 2 Corynanthine (1, 2 and 4 mg kg(-1)), an alpha(1)-adrenoceptor ant agonist and idazoxan (100, 200 and 300 mu g kg(-1)), an alpha(2)-adren oceptor antagonist were administered 10 min prior to ouabain. Corynant hine (2 and 4 mu g kg(-1)) showed significant increase in the amount o f ouabain required to cause arrhythmia and lethality, whereas idazoxan (200 and 400 mu g kg(-1)) decreased it. 3 Corynanthine inhibited the ouabain-induced presser response while idazoxan potentiated it. 4 Effe cts of these agents on the sympathetic nervous system appear to have p layed a significant role in its anti- and proarrhythmic actions.