The role of glutamine in skeletal muscle ischemia/reperfusion injury in the rat hind limb model

Glutamine and its relationship with intracellular redox status, oxidative stress and cell proliferation/death

Glutamine is a multifaceted amino acid used for hepatic urea synthesis, renal ammoniagenesis, gluconeogenesis in both liver and kidney, and as a major respiratory fuel for many cells. Decreased glutamine concentrations are found during catabolic stress and are related to susceptibility to infections. Besides, glutamine is not only an important energy source in mitochondria, but is also a precursor of the brain neurotransmitter glutamate, which is likewise used for biosynthesis of the cellular antioxidant glutathione. Reactive oxygen species, such as superoxide anions and hydrogen peroxide, function as intracellular second messengers activating, among others, apoptosis, whereas glutamine is an apoptosis suppressor. In fact, it could contribute to block apoptosis induced by exogenous agents or by intracellular stimuli. In conclusion, this article shows evidences for the important role of glutamine in the regulation of the cellular redox balance, including brain oxidative metabolism, apoptosis and tumour cell proliferation.

Skeletal muscle ischaemia-reperfusion injury: further characterisation of a rodent model

BACKGROUND

Postischaemic damage in skeletal muscle may be reflected in changes to microvascular blood flow, vascular permeability, and subsequent tissue viability. Previous preclinical studies have not addressed all these parameters, and have not used periods of ischaemia and reperfusion relevant to the clinical setting. This study aimed to develop an animal model hindlimb ischaemia-reperfusion to simulate acute lower limb ischaemia.

METHODS

A rodent model of hindlimb tourniquet-induced ischaemia-reperfusion was employed. Gastrocnemius muscle blood flow (GMBF; radio-labelled microspheres), oedema (GMO; using a wet:dry ratio method) and viability (GMV; histochemistry and computerised planimetry) were quantified.

RESULTS

6 h ischaemia per seresulted in neither muscle oedema nor loss of viability, but these changes were apparent following 4 h reperfusion. Early reperfusion at 10 min demonstrated low reflow, with GMBF improving at 120 min before declining sharply at 240 min.

CONCLUSION

Prolonged hindlimb ischaemia followed by reperfusion in this rodent model caused significant reductions in gastrocnemius muscle blood flow, associated with muscle oedema and necrosis. These three parameters have not been previously reported together in the same model. This reproducible model could be used in the evaluation of potential therapeutic intervention strategies aimed at ameliorating skeletal muscle reperfusion injury.

Effects of ovariectomy and estrogen on ischemia-reperfusion injury in hindlimbs of female rats

The effects of estrogen and ovariectomy on indexes of muscle damage after 2 h of complete hindlimb ischemia and 2 h of reperfusion were investigated in female Sprague-Dawley rats. The rats were assigned to one of three experimental groups: ovariectomized with a 17beta-estradiol pellet implant (OE), ovariectomized with a placebo pellet implant (OP), or control with intact ovaries (R). It was hypothesized that following ischemia-reperfusion (I/R), muscle damage indexes [serum creatine kinase (CK) activity, calpain-like activity, inflammatory cell infiltration, and markers of lipid peroxidation (thiobarbituric-reactive substances)] would be lower in the OE and R rats compared with the OP rats due to the protective effects of estrogen. Serum CK activity following I/R was greater (P < 0.01) in the R rats vs. OP rats and similar in the OP and OE rats. Calpain-like activity was greatest in the R rats (P < 0.01) and similar in the OP and OE rats. Neutrophil infiltration was assessed using the myeloperoxidase (MPO) assay and immunohistochemical staining for CD43-positive (CD43+) cells. MPO activity was lower (P < 0.05) in the OE rats compared with any other group and similar in the OP and R rats. The number of CD43+ cells was greater (P < 0.01) in the OP rats compared with the OE and R rats and similar in the OE and R rats. The OE rats had lower (P < 0.05) thiobarbituric-reactive substance content following I/R compared with the R and OP rats. Indexes of muscle damage were consistently attenuated in the OE rats but not in the R rats. A 10-fold difference in serum estrogen content may mediate this. Surprisingly, serum CK activity and muscle calpain-like activity were lower (P < 0.05) in the OP rats compared with the R rats. Increases in serum insulin-like growth factor-1 content (P < 0.05) due to ovariectomy were hypothesized to account for this finding. Thus both ovariectomy and estrogen supplementation have differential effects on indexes of I/R muscle damage.