Nitric oxide synthase in aging rat skeletal muscle.

The neuronal isoform of nitric oxide synthase (NOS) is expressed at high concentrations in skeletal muscle, and NO influences muscle contractility, glucose utilization, and free radical damage or protection. NOS activity and expression was evaluated in extensor digitorum longus (EDL), soleus, and diaphragm of 8 and 24 month old Fisher 344 rats. In 8-month-old animals, NOS activity was highest in EDL, which contained the highest percentage of NOS containing fibers, and was lowest in soleus. NOS activity and percentage of NOS containing fibers was significantly reduced in all muscle groups with age. To determine if NOS reduction correlated with free radical injury the level of lipid peroxidation, as measured by malonaldehyde equivalents, was determined. With age lipid peroxidation increased in EDL, was reduced in diaphragm, and showed a non-significant change in soleus. Therefore, a straightforward reduction of NOS activity does not correlate with lipid peroxidation. The reduction of NOS with age in skeletal muscle may be most significant for muscle metabolism and force production and be of limited significance for free radical metabolism.