The administration of oxytocin during early reperfusion, dose-dependently protects the isolated male rat heart against ischemia/reperfusion injury

In our previous study, the administration of oxytocin (OT) could precondition the heart against ischemia/reperfusion injury. In this study, to investigate the cardiac postconditioning effect of oxytocin, isolated rat hearts were mounted on a Langendorff perfusion apparatus. In all groups, the hearts underwent 30 min of regional ischemia followed by 120 min of reperfusion. In the ischemia/reperfusion (IR) group, ischemia and reperfusion was induced. In the ischemic postconditioning (Ipost) group, hearts underwent 6 cycles of 10 s reperfusion and 10 s ischemia at the beginning of reperfusion. In the other groups (III-IX), OT was perfused 5 min before the onset of reperfusion and continued for 25 min with following doses (Molar): 10− 12, 5 × 10− 12, 8 × 10− 12, 10− 11, 2 × 10− 11, 5 × 10− 11, and 10− 10. The infarct size and coronary effluent levels of creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH) and malondialdehyde (MDA) were calculated at the end of reperfusion. The infarct size decreased considerably in Ipost group compared to IR group (P < 0.05). Also, the infusion of oxytocin by doses of 8 × 10− 12 M, 10− 11 M and 2 × 10− 11 M dose-dependently reduced infarct size (P < 0.05) significantly compared to the IR group. LDH level in coronary effluent was markedly decreased in Ipost group and treatment with oxytocin by doses of 8 × 10− 12 M, 10− 11 M, 2 × 10− 11 M and 5 × 10− 11 M (P < 0.05) compared to IR group. Ipost, OT 2 × 10− 11and 10− 11 M significantly decreased CK-MB level (P < 0.05). Ipost, OT 8 × 10− 12, 10− 11 and 2 × 10− 11 M significantly decreased MDA level as compared to IR group. Our study shows that oxytocin dose-dependently exerts cardiac postconditioning.