These results indicate that hearts became more vulnerable to ischemia with age and that the beneficial effects of preconditioning were reversed in middle-aged rat hearts.

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Protection of the ischemic myocardium by pretreatment with a high dose of 2,3-butanedione monoxime (BDM) is attributed to the enhancement of glycolytic ATP production rather than to the inhibition of contracture during mild ischemia. Our objective was to investigate whether the inhibition of contracture would protect the arrested heart during prolonged ischemia. Isolated perfused rat hearts were subjected to 30 min of low-flow ischemia followed by reperfusion. Ischemic hearts were treated with BDM (5 mmol/l) after beating stopped. BDM ameliorated the increase in intraventricular pressure after ischemia without significant changes in ATP levels and with a decreased accumulation of lactate. BDM treatment accelerated the recovery of function and high-energy phosphates with reduced myocardial Ca2+ overload. The results of this study suggested that inhibition of contracture can protect the heart from ischemia-reperfusion injury.

To clarify the roles of subclasses of alpha 1-adrenoreceptors in ischemic-reperfused myocardium, we compared the effect of the nonselective alpha 1-blocker bunazosin with that of the alpha 1A-blocker WB4101 and the alpha 1B-blocker chlorethylclonidine (CEC) in isolated rat hearts. After 30 min of preperfusion, Langendorff-perfused hearts were subjected to 25 min of global ischemia followed by 30 min of reperfusion. Hearts were randomly divided into 4 groups, with one of the following substances being added to the perfusate: buffer alone (control), 10(-6) mol/L bunazosin, 10(-7) mol/L WB4101, or 10(-7) mol/L CEC. Bunazosin had a negative inotropic effect and preserved the postischemic ATP content, reduced the postischemic increase in intracellular Na+ content and then enhanced postreperfusion recovery of creatine phosphate. Bunazosin also reduced myocardial 45Ca2+ uptake during reperfusion (control 5.2 vs bunazosin 2.5 mumol/g dry weight of tissue (dwt), p < 0.01). However, the recovery of left ventricular developed pressure (DP) was not improved when bunazosin was added to the perfusate during reperfusion. WB4101 had neither a negative inotropic nor an energy-sparing effect, but it improved the recovery of DP (control 43% vs WB4101 56% of preischemic value, p < 0.05) with no reduction in myocardial 45Ca2+ uptake. CEC had a negative inotropic and energy-sparing effect and then reduced myocardial 45Ca2+ uptake (CEC 3.1 mumol/g dwt, p < 0.05), but it did not improve the recovery of DP. These results suggest that the preischemic administration of an alpha 1B-adrenoreceptor subtype blocker protected ischemic-reperfused myocardium via reduction of Ca2+ overload, whereas the selective blockade of the alpha 1A-adrenoreceptor subtype reduced myocardial damage via mechanism(s) other than Ca2+ metabolism.

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