Functional and histological characteristics of skeletal muscle and the effects of leptin in the genetically obese (ob/ob) mouse

BACKGROUND: Skeletal muscle mass in genetically obese (ob/ob) mice displays a reduced mass compared with their normal lean counterpart mice. However, the functional capacity of the available skeletal muscle mass in these anim als has not yet been determined. OBJECTIVE: To investigate the properties of skeletal muscle in ob/ob mice a nd determine the effects of leptin administration on skeletal muscle in the se mice. METHODS: Following 4 weeks of i.p, leptin administration (or control treatm ent) anaesthetized ob/ob and lean mice had their extensor digitorum longus and soleus muscles removed, and standard measures of isometric contractile properties and fatigability were performed. Histochemistry was used to dete rmine fibre type proportions and individual fibre areas of all muscles. RESULTS: Leptin had no effect on the morphology or function of ob/ob skelet al muscle despite reducing body mass in ob/ob mice. Force production was un altered in obese mice. However, a significant prolongation of contraction a nd relaxation times were evident. Obese skeletal muscle was also more fatig ue resistant. Fibre proportions displayed a more slow type profile in ob/ob skeletal muscle, and in conjunction with previous work a reduced ability t o hypertrophy. CONCLUSION: Skeletal muscle from obese mice is morphologically and function ally different from lean mouse skeletal muscle. Obese muscle is very simila r to skeletal muscle from aged mice, and the specific contractile propertie s examined appear to be determined by the fibre make-up of these muscles.