Loss of canine myocardial nicotinamide adenine dinucleotides determines the transition from reversible to irreversible ischemic damage of myocardial cells.

We investigated if the loss of nicotinamide coenzymes in ischemic-infarcted myocardium may be responsible for the transition from reversibly ischemic to irreversibly infarcted cell damage. The LAD was occluded in 6 dogs for 4 h. Transmural needle biopsies were taken from he ischemic-infarcted region after 1/2, 1, 11/2, 2, and 4 h of ischemia and further divided into subepicardial and subendocardial halves. At each time interval the concentration of the nicotinamide coenzymes NAD, NADH, and NADPH were measured, and the degree of cellular injury was evaluated by electron microscopy. The glycohydrolase activity (EC 3.2.2.5), the enzyme which splits NAD, was determined in brain, myocardium, kidney, and skeletal muscle of 4 rats. Total NAD, the sum of NAD and NADH, started to decrease significantly in the ischemic subendocardium 1 h after onset of ischemia. Degradation of NADPH occurred later. Loss ot total NAD was about 60-70% when electron microscopy diagnosed irreversible cell injury. The glycohydrolase activity was the highest in brain followed by myocardium, kidney, and skeletal muscle, reflecting the different tolerances of these tissues towards ischemia. The key mechanism for ischemic injury seems to be the tissue acidosis which activates the glycohydrolase leading to a loss of the vital coenzymes.