Role of calcium overload on coronary arterial stunning caused by myocardial ischemia reperfusion

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Transient myocardial ischemia attenuates pharmacological coronary vasodilation, suggesting attenuation of colonary blood flow(CBF) during reduction of coronary perfusion pressure after transient ischemia. To test this idea, 32 dogs were studied. CBF of the left anterior descending coronary artery was measured during stepwise reduction of coronary perfusion pressure by 10mmHg. In the control, reductions of CBF,fractional shortening(FS) and lactate extraction ratio (LER) were not observed during coronary perfusion pressure=100-70mmHg. Thirty min after 10 min of coronary occlusion, CBF response to adenosine (2mug/kg/min, ic) and papaverine (60mug/kg/min, ic) were attenuated by 34<plus-minus>9 and 26<plus-minus>7%, respectively, although FS,LER and basal CBF returned to control. During reduction of coronary perfusion pressure between 80-50mmHg, CBF and End/Epi flow ratio decreased by 9<plus-minus>5 and 35<plus-minus>9%, respectively, compared with the pre-ischemic condition. Both FS and LER were attenuated (p<.01) at coronary perfusion pressure=80-50mmHg (FS : 9.8<plus-minus>1.2 vs.20.6<plus-minus>1.2%, LER : -18.5<plus-minus>6.8 vs.26.7<plus-minus>3.6% at coronary perfusion pressure=70mmHg). Thus we conclude that transient ischemia mainly impairs autoregulation of endomyocadial flow, and causes myocardial contractile and metabolic dysfunction when coronary perfusion pres