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Limitations of ischemic tolerance in oxidative skeletal muscle: perfusion vs tissue protection
Amit Badhwar1, Alison A Dungey, Kenneth A Harris
1Lawson Health Research Institute and Department of Medical Biophysics, University of Western Ontario, N6A 4G5, London, Ontario, Canada.
Objectives:
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.