Nitric oxide myotoxicity is age related.

Nitric oxide (NO) is generated under normal conditions in skeletal muscle and acts as a messenger that influences contractility, blood flow, and glucose metabolism. Excess NO generation may occur in pathological states, in particular inflammatory conditions. We demonstrate that incubation of rat extensor digitorum longus muscle with the NO donor, S-nitrosocysteine, leads to release of creatine kinase, a marker of muscle injury after a delay of 90 min. Muscle of old animals was more sensitive to the NO donor. Light microscopic analysis does not show abnormalities, with the exception of an increase in interfiber distance. Histological staining identified no pathological elevations of calcium. The study demonstrates the direct toxicity of NO to skeletal muscle, and that muscle of older animals is differentially susceptible to NO toxicity.