Characterization of muscles from aspartic acid obese rats.

This study was undertaken to determine whether changes in muscle mass, muscle fiber diameter, or shifts in fiber type occur in the aspartic acid-injected rat, an animal model of hypothalamically induced obesity. We found that diaphragm, gastrocnemius, and soleus muscle mass was 140, 149, and 171% greater, respectively, in control compared with aspartic acid-injected rats. No differences were noted in heart weights. Significant reductions in mean fiber diameter of aspartic compared with control rats were present in each skeletal muscle. Furthermore, significant size reductions were noted for each fiber type in the diaphragm, with fast-glycolytic fibers showing the greatest reduction compared with controls at both 7 and 12 mo. Fiber type composition within the diaphragm did not differ between groups but showed a change with age. These results are compared with genetic models of obesity, the Zucker rat and the ob/ob mouse, as well as the ventromedial hypothalamic lesioned rat and the gold thioglucose mouse. Based on these results, the aspartic rat appears more similar to the two genetic models of obesity and also mimics some of the effects of malnutrition in rodents.