title: The role of nitric oxide synthase and heme oxygenase in the protective effect of hypothermia in ischemia-reperfusion injury.
abstract: BACKGROUND
  Ischemia-reperfusion injury plays an important role in limb salvage following limb ischemia. The purpose of the present study was to evaluate the effect of local hypothermia and chemical modulators on microvascular permeability following ischemia-reperfusion injury in skeletal muscle.
  
  
  METHODS
  Sprague-Dawley rats were randomized into nine groups. Postcapillary venules of the extensor digitorum longus muscle were visualized with use of intravital microscopy. Following an intravenous bolus of fluorescein isothiocyanate-labeled albumin, the intravascular and extravascular space was examined for leak. Rats in the sham group underwent a one-hour mock ischemic period without the application of a femoral artery tourniquet, followed by one hour of mock reperfusion. The treatment groups (n = 5 in each group) had the tourniquet applied for one hour, followed by one hour of reperfusion at 10 degrees C (cold) alone, at 10 degrees C with nitric oxide synthase inhibitor, at 10 degrees C with heme oxygenase inhibitor, at 10 degrees C with a combination of inhibitors, at 34 degrees C (warm) alone, at 34 degrees C with a heme oxygenase inducer, at 34 degrees C with a nitric oxide synthase inducer, or at 34 degrees C with a combination of inducers.
  
  
  RESULTS
  Rats in the sham group did not show a significant increase in microvascular permeability. Rats in the warm ischemia/reperfusion group displayed significant increases in microvascular permeability, as did the rats that received inhibitors of heme oxygenase and nitric oxide synthase at 10 degrees C. No significant increase in microvascular permeability was observed in the animals in the cold ischemia/reperfusion group or in animals that received inducers of heme oxygenase and nitric oxide synthase at 34 degrees C.
  
  
  CONCLUSIONS
  Local hypothermia protects skeletal muscle from increased microvascular permeability following ischemia-reperfusion injury. This protective effect is also seen with the induction of the nitric oxide synthase and heme oxygenase systems at physiologic temperature. We also have shown that the protective effects of hypothermia are blocked by giving heme oxygenase and nitric oxide synthase inhibitors while keeping the muscle hypothermic. These findings demonstrate that heme oxygenase and nitric oxide synthase play a combined role in ischemia-reperfusion injury, suggesting possible pathways for clinical intervention to modulate injury seen following trauma, tourniquet use, vascular surgery, and microvascular surgery.
authors.affiliation: Departments of Orthopaedic Surgery, Scott and White Memorial Hospital, 2401 South 31st Street, Temple, TX 76508, USA.
authors.forename: Russell
authors.initials: R
authors.lastname: Ward
authors.forename: Nicholas
authors.initials: N
authors.lastname: Souder
authors.forename: Daniel
authors.initials: D
authors.lastname: Stahl
authors.forename: Felicia
authors.initials: F
authors.lastname: Hunter
authors.forename: Robert
authors.initials: R
authors.lastname: Probe
authors.forename: Christopher
authors.initials: C
authors.lastname: Chaput
authors.forename: Ed
authors.initials: E
authors.lastname: Childs
mesh_terms: D000818:Animals; D006419:Heme Oxygenase (Decyclizing) / Q000502:physiology*; D007036:Hypothermia, Induced; D018482:Muscle, Skeletal / Q000098:blood supply*; D019001:Nitric Oxide Synthase / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015427:Reperfusion Injury / Q000209:etiology / Q000517:prevention & control*
chemical_list: D019001:Nitric Oxide Synthase; D006419:Heme Oxygenase (Decyclizing)