Thermal injury is known to cause increased muscle catabolism, but the mechanisms involved in this process are not clear. Diaphragms from thermally injured rats were removed and incubated in vitro on the third postburn day in order to determine the rates of protein synthesis and degradation using [14C]tyrosine uptake and release as an indicator of these processes. Diaphragms from rats that received 50% total body surface, full-thickness wounds and unburned sham-treated controls were examined. The rate of protein synthesis in the absence of insulin supplementation was found to decrease (26%) and the rate of protein degradation increased (81%) under these conditions. Insulin supplementation (0.1 U/ml) to the incubation media caused a significant increase (39%) in the rate of synthesis in the sham-controls but did not stimulate synthesis in the burned group. Degradation rates measured in the presence of insulin were increased in the burned group (64%), but were somewhat blunted in comparison to the insulin-deficient degradation rates (81%). These results indicate that diaphragm muscles from thermally injured rats show a decreased insulin stimulation of protein synthesis after injury, and insulin does not significantly alter the enhanced rate of protein degradation observed in these muscles after injury.
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