Background: Analyze the effects of ischemic postconditioning on skeletal muscle injury and apoptosis produced by partial ischemia and reperfusion in rats.
Materials and methods: An experimental study was designed using 70 Wistar rats divided in 3 groups: Sham; Control-submitted to ischemia and reperfusion; and Postconditioning-submitted to ischemia and reperfusion with ischemic postconditioning. Subgroups (n = 10) were divided by duration of ischemia (4, 5, or 6 hr). A partial ischemia model using aortic clamping was used. The postconditioning protocol consisted of 3 cycles of clamping the aorta for 1 min and releasing for another minute. Skeletal muscle injury was evaluated by measuring serum levels of releasing cytoplasmic enzymes: aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and total creatine phosphokinase (CPK). Lipid peroxidation was evaluated by muscular levels of malondialdehyde (MDA). Energetic cell storage was evaluated by muscular glycogen levels. Apoptosis was evaluated analyzing the expression of caspase 3 and protein B-cell lymphoma 2 (Bcl-2) by immunohistochemistry.
Results: AST levels in Sham group were 109.80 units/L, in Control subgroups were 4h 200.60 units/L/5h 392.30 units/L/6h 118.82 units/L, whereas in Postconditioning subgroups were: 4h 316.10 units/L/5h 268.40 units/L/6h 267.00 units/L. There was a 2-3-fold increase in Control and Postconditioning groups compared with Sham group (P = 0.003) There was no difference between groups with the same ischemic injury time. LDH, CPK, and MDA levels were similar in Sham, Control, and Postconditioning groups. Subgroups with the same ischemic injury time were also similar. Glycogen levels in Sham group were 0.629 mg%, in Control subgroups were 4h 0.323 mg%/5h 0.348 mg%/6h 0.183 mg%, whereas in Postconditioning subgroups were: 4h 0.443 mg%/5h 0.270 mg%/6h 0.324 mg%. Control and Postconditioning groups were decreased by half in relation with the Sham group (P = 0.002), with no difference between groups with the same ischemic injury time. For both caspase 3 and Bcl-2, the percentage of positive cells increased more than 2-fold in Control and Postconditioning groups when compared with Sham group (P < 0.001). The greater the ischemic injury time, the greater was the percent of positive cells (P < 0.0005), with no difference between subgroups with the same ischemic injury time.
Conclusions: Ischemic postconditioning had neither protective effect on skeletal muscle injury nor avoided apoptosis induction in rats submitted to partial ischemia and reperfusion.
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