Cardiotoxic effects of 5-fluorouracil in the guinea pig

In order to search into the underlying mechanisms of ECG changes suggestive of ischemia observed in humans and in rabbits after administration of 5-fluorouracil (5-FU), experiments were performed in anesthetized open-chest guinea pigs. The substance produced similar ECG changes in this species as well, after a rather long latent period of around 3 hours after intravenous administration. The incidence of ECG abnormality in animals given 60 mg/kg was 7/7, while that in animals given 30 mg/kg was 4/9. with 10-20 mg/kg, ECG changes were not observed during an experimental period as long as 5 hours. Associated with these ECG changes, a depletion of the high-energy phosphate compounds of the ventricular myocardium was observed. Analysis of tricarboxylic acid cycle (TCA cycle) intermediates revealed an accumulation of citrate within the myocardium, suggesting a malfunction of TCA cycle resulting from an inhibition of aconitase by fluorocitrate, as a cause of depletion of the high-energy phosphates. It is highly probable that the accumulation of citrate was due to the formation of fluoroacetate, an inhibitor of aconitase, from 5-FU via alpha-fluoro-beta-alanine, a major degradation product of 5-FU, for it is known that beta-alanine is usually converted to acetate.