Xanthine oxidase/dehydrogenase release following ischemia in isolated rat hearts

The release of xanthine oxidase/dehydrogenase XO/XDH (4.99 +/- 1.08 x 10(-12) moles/min/g wet wt in aerobic hearts) was not significantly increased following 30 min of ischemia, but almost doubled following 45 min of ischemia, indicating some endothelial cell damage. This release, however, was small compared to the release induced by digitonin perfusion (26 fold increase in an equivalent volume of effluent) and was nearly 1000 fold less than the enzyme activity measured in the tissue homogenate. There was a significant decrease in cardiac function (heart rate and systolic pressure) following 30 min of ischemia and no recovery of function following 45 min of ischemia and reperfusion. Endothelial cell damage determined by XO/XDH release is negligible during times of ischemia that cause severe damage to myocardial contractility. Coronary endothelial cells should not contribute significantly to circulating XO/XDH levels following ischemia.