Evidence for calcitonin gene-related peptide-mediated ischemic preconditioning in the rat heart

Previous studies have suggested that calcitonin gene-related peptide (CGRP) may play an important role in the mediation of ischemic preconditioning. In the present study, we examined the release of CGRP during ischemic preconditioning and the effect of preconditioning frequency on this effect in the isolated rat heart. Thirty minutes of global ischemia and 40 min of reperfusion caused a significant cardiac dysfunction and an increase in the release of creatine kinase (CK) during reperfusion. Preconditioning with one, two or three cycles of 5-min ischemia and 5-min reperfusion caused a marked improvement of cardiac function and a decrease in the release of CK, and there was no difference in the degree of improvement among groups. The protective effects of ischemic preconditioning were abolished by the CGRP receptor antagonist CGRP(8-37). A single preconditioning cycle induced a significant increase in the release of CGRP in the coronary effluent. In the hearts treated with two or three preconditioning cycles, the level of CGRP was highest in the first cycle, and was gradually decreased with increasing number of cycles of preconditioning. These results suggest that the protective effects of ischemic preconditioning are mediated by endogenous CGRP in the isolated rat heart.