Coronary flow rate dependent enzyme release rate from normoxic and anoxic rat hearts in vitro

To study the relation between coronary flow rate (CFR) and the rate of enzyme release from isolated perfused rat hearts which were either normoxic or anoxic, we measured the total activity of lactate dehydrogenase (LDH) released from the heart during a 3 h test period and mean CFR during that period. The test period consisted of (under)perfusion in the presence of oxygen and sodium pyruvate (normoxic ischaemia) or (under)perfusion in the absence of oxygen and metabolic substrates (anoxic ischaemia). Activity of LDH released during the 3 h test period correlated positively with mean CFR during anoxic ischaemia for the whole range of CFR from 0 to 17 ml·min−1, and during normoxic ischaemia when CFR was in the range 0 to 7 ml·min−1. At a CFR higher than 7 ml·min−1, the activity of LDH released during 3 h of normoxic ischaemia correlated negatively with CFR. Mean CFR was negatively correlated with coronary vascular resistance at the end of the 3 h period of perfusion. In the hearts subjected to normoxic ischaemia, coronary vascular resistance correlated positively with the percentage of myocardium unperfused. This study shows that a low CFR leads to unhomogeneous myocardial perfusion, which inhibits leakage of enzymes from myocytes into the perfusate.