Ischemic Preconditioning of Skeletal Muscle

Ischaemia and reperfusion effects on skeletal muscle tissue: morphological and histochemical studies

This was a study on the oxidative stress due to ischaemia (I) and reperfusion (R) in skeletal muscle tissue. Using a tourniquet, groups of rats were submitted to ischaemia for 4 h, followed by different reperfusion periods. The animals were divided in four groups: control; 4 h of ischaemia (IR); 4 h of ischaemia plus 1 h reperfusion (IR-1 h); 4 h of ischaemia plus 24 h reperfusion (IR-24 h); and 4 h of ischaemia plus 72 h reperfusion (IR-72 h). At the end of the procedures, samples of soleus muscle were collected and frozen in n-hexane at -70 degrees C. Cryostat sections were submitted to haematoxylin-eosin, succinate dehydrogenase (SDH) and nicotinamide adenine dinucleotide-tetrazolium reductase (NADH-TR) stains. An additional muscle sample was processed for electron microscopy. No alterations were found in control animals. IR group showed fibres had normal aspect besides some round, acidophilic and hypertrophic fibres. There were several fibres with angular outlines and smaller diameters in this group compared with control group. NADH-TR/SDH reaction was moderately intense in most fibres. In some fibres, cytoplasm showed areas without activity and other fibres had very intense reactivity. IR-1 h group showed oedema hypercontracted fibres with disorganized myofibrils, mitochondria with focal lesions and dilated sarcoplasmic reticulum. NADH-TR/SDH reaction was moderate to weak. IR-24 h showed intense inflammatory infiltrate in the endomysium and perimysium. NADH-TR/SDH reaction was similar to IR-1 h. IR-72 h showed necrotic fibres, areas with inflammatory infiltrate, reduced muscle fibres at different stages of necrosis and phagocytosis, and many small round and basophilic fibres characterizing a regeneration process. NADH-TR/SDH reaction was weak to negative. Our results suggest that ischaemia and the subsequent 1-, 24- and 72-h reperfusions induced progressive histological damage. Although progressive, it may be reversible because there were ultrastructural signs of recovery after 72-h reperfusion. This recovery could in part be due to the low oxidative stress identified by the morphological and histochemical analysis.

The Effect of Ischemic Preconditioning on Secondary Ischemia in Skin Flaps

Ischemic preconditioning is a useful manipulation to reduce the undesirable effects of ischemia. The beneficial results of this phenomenon against ischemia-reperfusion have been seen in different flap models; however, all these studies have focused on primary ischemia. In this study, we investigated the effects of ischemic preconditioning on secondary ischemia in a skin flap model. We used the 6- x 3-cm-sized epigastric skin flap in 40 Wistar rats. In all animals, primary global ischemia of 2 hours was followed by 4 hours of either arterial or venous secondary ischemia 24 hours after the primary ischemia and ischemic preconditioning (IP) was tested in this protocol. Ischemic preconditioning was performed by 2 cycles of 15 minutes of repeated ischemia/reperfusion periods. The animals were allocated into 4 groups: group 1 (n = 10 animals): primary ischemia (2 hours) + secondary arterial ischemia (4 hours); group 2 (n = 10 animals): IP + primary ischemia (2 hours) + secondary arterial ischemia (4 hours); group 3 (n = 10 animals): primary ischemia (2 hours) + secondary venous ischemia (4 hours); group 4 (n = 10 animals): IP + primary ischemia (2 hours) + secondary venous ischemia (4 hours). Flap viability was assessed 1 week after the surgical procedure, and surviving flap area was recorded as a percentage of the whole flap area. Group 1 was compared with group 2, and group 3 was compared with group 4 to evaluate the effects of ischemic preconditioning against secondary arterial and venous ischemia. t test and Mann-Whitney rank sum tests were used for statistical analysis. There were statistical differences both between groups 1 and 2 and groups 3 and 4. The results revealed that ischemic preconditioning was an effective procedure to reduce the flap necrosis as a cause of secondary ischemia in skin flaps.