Oxidative capacity of liver and muscle from genetically obese rats

Abstract

The contribution of muscle tissue to the Increased metabolic efficiency of the obese (fa/fa) zucker rat at 6 weeks of age was examined, in vitro oxygen consumption was similar in obese and nonobese soleus and extensor dlgltorum longus (EDL) muscles, whether the animals were in an ad libitum fed, fasted, or triiodothyronlne-stlmulated state. NO phenotypic difference in in vitro oxygen consumption was seen when the muscles were preincubated with insulin, py­ ruvate kinase, citrate synthase, succinate dehydrogenase, and cytochrome oxidase activities were phenotypically simi­ lar in the soleus and the EDL muscles, phosphofructokinase and lactate dehydrogenase activities were increased in the obese soleus, while hexokinase activity was in­ creased in the nonobese EDL* Mitochondrial and whole muscle homogenate respiration rates were similar in both phenotypes. The soleus and EDL muscles from the obese animals weighed less than those from the nonobese, but empty carcass weights were similar. Taken together these data suggest that muscle mass, muscle oxygen consumption, and muscle oxidative capacity are similar in 6 week old obese and nonobese rats. Therefore, defective energy metabolism in muscle probably does not contribute to the Increased metabolic efficiency of the young obese rat.