Glucose metabolism of injured skeletal muscle: the contribution of inflammatory cells.

Wounded muscle which has increased glucose uptake is infiltrated with a large number of inflammatory cells. Macrophages which are the predominant inflammatory cells in wounded muscle can increase glucose oxidation by epididymal fat pads. Therefore, the possibility that inflammatory cells could also alter glucose metabolism in skeletal muscle was investigated. Peritoneal inflammatory cells (67% macrophages, 7% lymphocytes, 15% polymorphonuclear leukocytes, and 11% eosinophils) were elicited with a 1% sodium caseinate solution. Extensor digitorum longus muscles, were incubated alone, in the presence of inflammatory cells or in an inflammatory-cell-conditioned media. Similar incubations were performed using epididymal fat pads. In addition, inflammatory cells were incubated alone. The present studies confirmed the previous finding that inflammatory cells release a factor(s) that increases glucose oxidation in epididymal fat pads. The coincubation of inflammatory cells with skeletal muscle resulted in a 22% increase in glucose uptake and a 19% increase in the conversion of glucose to lactate compared to the sum of these processes for muscle or inflammatory cells incubated alone. In addition, this study showed that the incubation of skeletal muscle in inflammatory-cell-conditioned medium produced a 117.6% increase in glucose uptake and a 147% increase in the conversion of glucose to lactate. Therefore, inflammatory cells can increase glucose metabolism in skeletal muscle through the release of a soluble factor(s). This effect does not require a direct contact of the inflammatory cells with skeletal muscle.