Ultrastructural Alterations During the Critical Phase of Reperfusion: A Stereological Study in Buffer-Perfused Isolated Rat Hearts

The present study focuses on myocardial ultrastructural alterations during the early phase of reperfusion. Isolated buffer-perfused rat hearts were exposed to standard perfusion (control group, n = 10); 60 min of global ischemia (n = 10); 60 min of global ischemia followed by 2 min of reperfusion (n = 10); or 60 min of global ischemia followed by 10 min of reperfusion (n = 10). The hearts were perfusion-fixed for electron microscopy, and ultrastructural evaluation was performed using stereological technique in order to obtain an estimate of the volume fraction and absolute volume of different tissue components. Effect of ischemia: Neither the ventricular nor the myocytic volume differed significantly from the respective control values. Both the myocytic mitochondrial volume (135 ± 8 vs control 89 ± 6 μl) and the volume of myocytic clear space (35 ± 6 vs control 10 ± 2 μl) were significantly increased. The capillary volume (22 ± 4 vs control 58 ± 6 μl) and the volume of the capillary lumen (15 ± 3 vs control 48 ± 5 μl) were significantly decreased. The volume of the capillary wall, however, was not altered after exposure to ischemia (7 ± 3 vs control 10 ± 1 μl). Additive effect of ischemia and reperfusion: Both the ventricular volume (755 ± 28 vs control 600 ± 32 μl) and the myocytic volume (396 ± 24 vs control 287 ± 16 μl) were significantly increased after 10 min of reperfusion. Effect of reperfusion: The ischemic-induced myocytic mitochondrial swelling and increase of clear space were not reinforced during reperfusion. Furthermore, the volume of the capillary lumen and the capillary wall did not alter significantly in the groups exposed to reperfusion compared to the ischemic hearts. In conclusion, stereological evaluation did not reveal significant aggravation of ischemic-induced myocardial injury during the early phase of reperfusion. Cardiovascular Pathol 1999;8:279–289