Effect of actinomycin D and cycloheximide on ischemic preconditioning-induced delayed cardioprotective effect in rats

The present study was designed to investigate the effect of actinomycin D, a transcription inhibitor, and cycloheximide, a translation inhibitor, on the delayed cardioprotective effect of ischemic preconditioning. Left thoracotomy was performed in anaesthetized rats at 4th/5th intercostal space and polypropylene suture (5-0) was employed to occlude left common coronary artery. Ischemic preconditioning was produced by four episodes of 5 min of coronary artery occlusion followed by 5 min of reperfusion and thoracic cavity was sutured. Left thoracotomy was performed again after 24 hr of ischemic preconditioning and left coronary artery was occluded for 30 min followed by reperfusion for 120 min. Area at risk and infarct size was estimated by patent blue and TTC staining respectively. Total left ventricular RNA was isolated and estimated quantitatively. Ischemic preconditioning, 24 hr after its induction, produced significant decrease in myocardial infarct size occurred as a result of sustained ischemia and reperfusion but produced no marked effect on ventricular RNA content. Actinomycin D and cycloheximide only, in high dose, markedly attenuated ischemic preconditioning induced decrease in myocardial infarct size. However, no such effect was noted with low dose of cycloheximide. The results suggest that delayed cardioprotective effect of ischemic preconditioning may be mediated through denovo synthesis of protein(s) which is regulated both at transcriptional and translational level.