REPERFUSION AT REDUCED FLOW-RATES ENHANCES POSTISCHEMIC CONTRACTILE RECOVERY OF PERFUSED HEART

The effects of reperfusion at reduced flow rates on postischemic cardi ac contractile function were examined in perfused rat hearts. Isolated hearts were subjected to 35-min ischemia followed by reperfusion at t he preischemic flow rate (9.0 ml . g(-1). min(-1); ordinary flow rate) or at reduced flow rates (0.9-8.1 ml . g(-1). min(-1)). Reperfusion a t ordinary flow rate did not generate any left ventricular developed p ressure (LVDP), whereas reperfusion at reduced flow rates (0.9-7.2 ml . g(-1). min(-1)) elicited 13-57% of initial contractile force at repe rfusion's end; optimal recovery occurred at 3.6 ml . g(-1). min(-1) (r educed flow rate). Reduced flow rate reperfusion attenuated ischemia-r eperfusion-induced increase in left ventricular end-diastolic pressure (LVEDP) and perfusion pressure (PP), alteration in tissue Na+, K+, Ca 2+, and Mg2+, release of creatine kinase and ATP metabolites, and deve lopment of triphenyltetrazolium chloride-unstained areas. Enhanced pos tischemic LVDP recovery was inversely related to higher coronary PP at the initial stage (4 min) of reperfusion (r = -0.763). The benefit of reduced flow rate reperfusion could not be attributed to rate of calc ium delivery to the heart, formation of oxygen free radicals in myocar dium, endothelium-dependent coronary artery dilation, or LVDEP reducti on. Enhancement of postischemic LVDP recovery was associated with atte nuation of ischemia-reperfusion-induced increases in myocardial sodium and calcium; failure of postischemic LVDP recovery was accompanied by an increase. Reduction in sodium and calcium overload may underlie th e beneficial effects of reduced flow rate reperfusion in ischemic-repe rfused heart.