| Abstract: | The purpose of the present study was to compare tissue oxidative capacity, skeletal muscle fatty acid composition, and tissue fuel stores in low-fat fed (LFD, 12% of energy from corn oil) male Wistar rats, and in high-fat fed (45% of energy from corn oil) obesity-prone (OP) and obesity-resistant (OR) male Wistar rats. Designation of OP and OR rats was based on body weight gain (upper tertile for OP; lower tertile for OR) after 5 weeks on the high-fat diet. Body weight gain over the 5-week dietary period was 91 ± 9 g in LFD, 98 ± 4 g in OR, and 158 ± 5 g in OP (p<0. 05 vs. LFD and OR). Energy intake over the 5-week dietary period was 3099 ± 101 kcal in LFD, 3185 ± 51 kcal in OR, and 3728 ± 45 kcal in OP (p<0. 05 vs. LFD and OR). Maximal citrate synthase activity (μ. mol?1min?1) in the gastrocnemius muscle was not significantly different among groups: 12. 1 ± 2. 4 in LFD, 11. 4 ± 1. 9 in OR and 133 ± 2. 5 in OP rats. Similarly, citrate synthase activity in the heart, 59. 3 ± 7. 2, and liver, 6. 6 ± 0. 4, was also not significantly different among groups. Fatty acid composition of the gastrocnemius muscle was not significantly different among groups. Fasting glycogen levels in the liver, gastrocnemius muscle, and heart were 6. 4 ± 3. 7, 13. 2 ± 2. 3 and 6. 8 ± 1. 9 μmol/g in LFD, 21. 2 ± 5. 1 (p<0. 05 vs. LFD and OP), 10. 4 ± 1. 8 and 5. 9 ± 1. 1 mUmol/g in OR, and 36. 3 ± 4. 8 (p<0. 05 vs. LFD and OR), 10. 2 ± 23 and 53 ± 2. 1 μmol/g in OP rats, respectively. Triglyceride levels were similar among groups in plasma, heart and gastrocnemius muscle, but were significantly (p<0. 05) higher in the liver of OP (15. 5 ± 1. 9 (μmol/g) compared to OR (9. 1 ± 1. 1 μmol/g) and LFD (8. 1 ± 1. 4 μmol/g) rats. These data suggest that susceptibility to dietary obesity, in this rodent model, cannot be explained by differences in tissue oxidative capacity or muscle fatty acid composition. |
