A Novel Animal Model to Evaluate Oxygen Derived Free Radical Damage in Soft Tissue

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Abstract
We present a novel animal model which allows the continuous intra-arterial infusion in one hindlimb of non-anaesthetized rats, without inducing ischemia. Using this model the effect of continuous infusion (lml/h) for 24 h with tert-butylhydroperoxide (tert-BuOOH) at a concentration of 25mM on soft tissue of the left hind limb was studied and compared to the effect of saline infusion (control group). The tert-BuOOH-infused foot showed increased skin temperature, increased circumference, redness of the plantar skin, impaired function and increased pain sensation, while in the contralateral foot and in rats only perfused with saline these signs of inflammation were absent (p < 0.01). Histological analysis of the left gastrocne-mius muscle showed edema, muscle cell degeneration with a patchy distribution pattern and vascular damage. All these features increased in severity from 4 to 24 h of tert-BuOOH infusion. After 24 h of tert-BuOOH infusion infiltration of neutrophils in the interstitiuni was observed. Vascular permeability, expressed as left to right gastrocnemius muscle 99mmTc-IgG uptake ratio, was similarly increased after 4 h (2.09 ± 0.26) and 12 h (2.04 ± 0.08) of tert-BuOOH infusion compared to saline (1.05 ± 0.08) (p < 0.001), and further increased after 24 h (3.84 ± 0.13): (p < 0.001). In this animal model free radical-related soft tissue damage was induced, by continuous infusion of tert-BuOOH, followed by increasing necrosis and vascular permeability in skeletal muscle coinciding with neutrophilic infiltration.