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 ex posed to standard perfusion (control group, n = 10); 60 min of global ische mia (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 ultrastr uctural 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 myoc ytic volume differed significantly from the respective control values. Both the myocytic mitochondrial volume (135 +/- 8 vs control 89 +/- mu l) and t he volume of myocytic clear space (35 +/- 6 vs control 10 +/- 2 mu l) were significantly increased. The capillary volume (22 +/- 4 vs control 58 +/- 6 mu l) and the volume of the capillary lumen (15 +/- 3 vs control 48 +/- 5 mu l) were significantly decreased. The volume of the capillary wall, howev er, was not altered after exposure to ischemia (7 +/- 3 vs control 10 +/- 1 mu l) Additive effect of ischemia and reperfusion: Both the ventricular vo lume (755 +/- 28 vs control 600 +/- 32 mu l) and the myocytic volume (396 /- 24 vs control 287 +/- 16 mu l) were significantly increased after 10 min of reperfusion. Effect of reperfusion: The ischemic-induced myocytic mitoc hondrial swelling and increase of clear space were not reinforced during re perfusion. Furthermore, the volume of the capillary lumen and the capillary wall did not alter significantly in the groups exposed to reperfusion comp ared to the ischemic hearts. In conclusion, stereological evaluation did no t reveal significant aggravation of ischemic-induced myocardial injury duri ng the early phase of reperfusion. (C) 1999 by Elsevier Science Inc.