The initial phase of myocardial reperfusion is not associated with aggravation of ischemic-induced ultrastructural alterations in isolated rat heartsexposed to prolonged global ischemia

The present study focuses on the qualitative and sequential development of myocardial ultrastructural changes during the first 10 min of reperfusion i n isolated rat hearts exposed to 60 min of global ischemia. The frequency o f and the association between ultrastructural changes were examined by semi quantitative morphometry using the micrograph as unit. In each micrograph t he subcellular components of the myocytes (sarcolemma, mitochondria, myofil aments and nucleus) and the endothelial cells were evaluated and graded as slightly, moderately, or severely altered. Ischemia alone induced moderate to severe ultrastructural alterations. The myocytes revealed sarcolemmal di sattachment or rupture. The myocytic mitochondria had a clear matrix with a bundant broken cristae and amorphous matrix densities. The myofilamental pa ttern was irregular or even disrupted, and most nuclei had reduced density and showed margination of chromatin. The endothelium showed vacuolization, rupture of the plasma membrane, and extracellular accumulation of cellular debris. During the first 2 min of reperfusion severe ultrastructural altera tions were partly reversed. After 10 min of reperfusion both the frequency and grade of myocardial ultrastructural alternations were similar to that o bserved after ischemia. Cristal adhesions occurred predominately during rep erfusion and were associated with moderately and severely altered myocytic mitochondrial alterations. In conclusion, the results showed that ischemic- induced ultrastructural alterations were transiently improved upon reperfus ion. With exception of the development of cristal adhesions, the acute phas e of reperfusion was not associated with additional ultrastructural changes in isolated buffer-perfused rat hearts exposed to prolonged ischemia.