title: Limitations of ischemic tolerance in oxidative skeletal muscle: perfusion vs tissue protection.
abstract: OBJECTIVE
  This study determined if ischemic tolerance occurs in oxidative skeletal muscle following a severe ischemia/reperfusion (I/R) insult and if such protection involves the induction of nitric oxide synthase (NOS).
  
  
  METHODS
  The soleus muscle of male Wistar rats (250-350 g) was preconditioned (PC + I/R) using five cycles of ischemia (10 min) and reperfusion (10 min) or had no PC (I/R) and 24 h later 2 h no-flow ischemia was induced. Calcium dependent (cNOS) and independent (iNOS) NOS activities were determined from PC (n = 5), or sham (n = 5) and the role of iNOS was tested by application of aminoguanidine (AMG) (100 microM; n = 4) to the muscle bath. Direct measures of the number of perfused capillaries (Npc; #/mm) during 90-min reperfusion were obtained using intravital microscopy. Tissue injury was estimated using the fluorescent vital dyes ethidium bromide (E; labels injured cells) and bisbenzimide (B; labels all cells) and expressed as the ratio E/B.
  
  
  RESULTS
  PC prevented microvascular flow deficits (Npc:I/R = 23.4 +/- 1.3 vs PC + I/R = 29.9 +/- 1.1) and resulted in a modest, but significant reduction (21%) in tissue injury (I/R = 0.82 +/- 0.03 vs PC + I/R = 0.64 +/- 0.04). PC led to a nine fold increase in iNOS activity, but decreased cNOS activity by 94% compared to sham. AMG prevented the parenchymal protection following PC, but had no effect on microvascular perfusion.
  
  
  CONCLUSIONS
  Ischemic tolerance, 24 h following PC, preserved microvascular perfusion, but only modestly improved tissue viability in the soleus muscle.
authors.affiliation: Lawson Health Research Institute and Department of Medical Biophysics, University of Western Ontario, N6A 4G5, London, Ontario, Canada.
authors.forename: Amit
authors.initials: A
authors.lastname: Badhwar
authors.forename: Alison A
authors.initials: AA
authors.lastname: Dungey
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Harris
authors.forename: Jeremy A
authors.initials: JA
authors.lastname: Scott
authors.forename: Sarah D
authors.initials: SD
authors.lastname: McCarter
authors.forename: Jeffery R
authors.initials: JR
authors.lastname: Scott
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Forbes
authors.forename: Richard F
authors.initials: RF
authors.lastname: Potter
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D007511:Ischemia / Q000503:physiopathology*; D019194:Ischemic Preconditioning; D008297:Male; D008833:Microcirculation / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000098:blood supply*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D015424:Reperfusion; D015427:Reperfusion Injury / Q000517:prevention & control
chemical_list: D004791:Enzyme Inhibitors; D006146:Guanidines; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; C004479:pimagedine; D002118:Calcium