Limitations of ischemic tolerance in oxidative skeletal muscle: perfusion vs tissue protection.
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.
Badhwar
Amit
A
Lawson Health Research Institute and Department of Medical Biophysics, University of Western Ontario, N6A 4G5, London, Ontario, Canada.
Dungey
Alison A
AA
Harris
Kenneth A
KA
Scott
Jeremy A
JA
McCarter
Sarah D
SD
Scott
Jeffery R
JR
Forbes
Thomas L
TL
Potter
Richard F
RF
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
D004791:Enzyme Inhibitors; D006146:Guanidines; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; C004479:pimagedine; D002118:Calcium