Contribution of coronary endothelium to high resistance against hypoxia-reoxygenation injury in neonatal rat hearts

Abstract

Respective functional changes of myocardium, vascular smooth muscle and coronary endothelium induced by hypoxia (Hx)-reoxygenation (Rx) were compared between neonatal and adult hearts. Isolated, Langendorff-perfused hearts of neonatal (7 days) and adult (10 weeks) rats were subjected to 45-min Hx followed by 30-min Rx. Recovery of pressure rate product (PRP) after Rx was significantly better in neonatal hearts, with recovery to 9.96 ± 5.84 and 73.39 ± 12.85% in adult and neonatal hearts, respectively. Creatine kinase (CK) and troponin T released after Rx were significantly less in neonatal hearts. When the hypoxic period was prolonged to 150 min in neonatal hearts to match the extent of PRP reduction, recovery of PRP after Rx was better and CK leakage was significantly less than in adult hearts treated by 45-min Hx-Rx. The decrease in coronary perfusion pressure (CPP) induced by endothelium-independent vasorelaxant (adenosine) was not affected in either group. However, the response to the endothelium-dependent relaxant (bradykinin), decreased significantly after Rx in adult hearts (9.29 ± 1.05 to 2.94 ± 2.26%; p < 0.05) but not in neonatal hearts (13.42 ± 3.30 to 10.57 ± 4.95%; NS). In the early Rx phase, the release of prostanoids increased significantly in adult, but not in neonatal hearts, with increases of 70.09 ± 28.96 and −22.45 ± 13.78% in adult and neonatal hearts, respectively. These results indicate that neonatal hearts show higher resistance to Hx-Rx than adult hearts in endothelium as well as in myocardium.