ULTRASTRUCTURAL-CHANGES IN THE MYOCARDIAL MYOCYTIC MITOCHONDRIA - CRUCIAL STEP IN THE DEVELOPMENT OF OXYGEN RADICAL-INDUCED DAMAGE IN ISOLATED RAT HEARTS

The present study focuses on the sequential development of myocardial ultrastructural changes produced by oxygen radicals. Isolated rat hear ts were perfused with oxygen radicals, generated by hypoxanthine and x anthine oxidase, for 5 and 10 min followed by a 35-min recovery period . The frequency of, and the association between, ultrastructural chang es were examined by semiquantitative morphometry using the micrograph as unit. In each micrograph sarcolemmal, myocytic mitochondrial and my ofilamental alterations were observed and graded as slight, moderate o r severe. The myocytic nucleus and the endothelial cells were scored a s normal or altered. Five min group: Among the cellular organelles exa mined, the myocytic mitochondria showed the highest frequency of alter ation (in 15.3% of the micrographs). Among the grades of myocytic mito chondrial ultrastructural changes, slight alterations predominated (12 .5%). Slight myocytic mitochondrial alterations were not significantly associated with the occurrence of ultrastructural changes of other ce llular organelles. Endothelial ultrastructural alterations were sparse (1.5%). Ten min group: The frequency of altered organelles was greate r when compared to the 5 min group. The myocytic mitochondria were sti ll the most frequently altered component (61.7%), and myocytic mitocho ndrial ultrastructural alterations of all grades were strongly associa ted with the occurrence of other myocytic ultrastructural changes. In conclusion, the present study showed that myocytic mitochondrial chang es predominated after both 5 and 10 min of oxygen radical exposure fol lowed by recovery. In the 5 min group slight myocytic mitochondrial ch anges appeared independent of other myocardial changes, but in the 10 min group, however, myocytic mitochondrial changes were strongly assoc iated with other myocardial ultrastructural changes. These results ind icate that myocytic mitochondria are especially vulnerable to oxygen r adicals, and further that myocytic mitochondrial ultrastructural chang es may be a crucial step in the development of oxygen radical-induced myocardial damage.