Tyramine-like effect of cyclocytidine (2,2'-anhydro-1-beta-arabinofuranosylcytosine hydrochloride), an antineoplastic agent.

Since cyclocytidine (2,2'-anhydro-1-beta-arabinofuranosylcytosine hydrochloride) was introduced as an antineoplastic agent for the treatment of lymphatic leukemia, sinus acceleration and an increase in systemic blood pressure has been reported as its systemic effects in the clinical cases. These cardiovascular effects of cyclocytidine were observed also in anesthetized dogs, but not in reserpine-pretreated animals. Increases in heart rate and in systemic blood pressure were prevented by propranolol and phentolamine, respectively. The mechanism of these sympathomimetic effects was further analysed in the excised, blood-perfused canine sinoatrial node and papillary muscle preparations with a support dog. Positive chronotropic and inotropic responses to cyclocytidine were abolished by desipramine, propanolol, and pretreatment with reserpine but not by tetrodotoxin and hexamethonium. The tyramine-like actions of cyclocytidine at adrenergic neuronal terminals were discussed in conjunction with the uptake mechanism of the drug into the tumor cells.