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London Health Sciences Centre Research Incorporated and the Departments of 1 Surgery, 2 Medical Biophysics, 3 Physiology, and 4 Pharmacology and Toxicology, University of Western Ontario, London, Ontario, Canada N6A 4G5
We tested the hypothesis that ischemic preconditioning (PC) of skeletal muscle provided tolerance to a subsequent ischemic event 24 h later, and that such protection was due to nitric oxide (NO). Male Wistar rats, anesthetized with halothane, were randomly assigned to groups: ischemic (no PC; n = 11), PC (n = 11), PC + N-nitro-L-arginine methyl ester (L-NAME; 100 µmol/l; n = 5), PC + N-nitro-D-arginine methyl ester (100 µmol/l; n= 4), PC + aminoguanidine (AMG; 100 µmol/l; n = 4), ischemic + L-NAME (n= 4), or ischemic + AMG (n = 4). PC consisted of 5× 10 min of ischemia and reperfusion, and, 24 h later, 2 h of ischemia were induced by a tourniquet applied to the limb. With the use of intravital microscopy, the number of perfused capillaries (Npc) in the extensor digitorum longus (EDL) muscle was measured over a 90-min reperfusion period. The ratio of ethidium bromide- to bisbenzimide-labeled nuclei was used to estimate tissue injury. PC preserved Npc (23.6 ± 2.5) following 2 h of ischemia compared with sham muscles (11.5 ± 5.1), significantly elevating inducible NO synthase (iNOS) activity (81% increase), but did not afford protection to the parenchyma. L-NAME and AMG prevented ischemia-reperfusion-induced reduction in Npc in muscles without PC. However, after 90 min of reperfusion, L-NAME (Npc = 15.0 ± 1.7), but not AMG (Npc = 22.8 ± 3.1), significantly reduced the microvascular protection afforded by PC. We conclude that PC of the EDL muscle resulted, 24 h later, in protection to microvascular perfusion only, and that such protection was due to NO from sources other than iNOS.
ischemic preconditioning; microvascular perfusion; tissue injury
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