TISSUE OXIDATIVE CAPACITY, FUEL STORES AND SKELETAL-MUSCLE FATTY-ACIDCOMPOSITION IN OBESITY-PRONE AND OBESITY-RESISTANT RATS

The purpose of the present study was to compare tissue oxidative capac ity, 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 (OF) and o besity-resistant (OR) male Wistar rats. Designation of OP and OR rats was based on body weight gain (upper tertile for OF; lower tertile for OR) after 5 weeks on the high-fat diet. Body weight gain over the 5-w eek 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 die tary 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 syntha se activity mu mol . g(-1). min(-1)) in the gastrocnemius muscle was n ot significantly different among groups: 12.1 +/- 2.4 in LFD, 11.4 +/- 1.9 in OR and 13.3 +/- 2.5 in OP rats. Similarly, citrate synthase ac tivity in the heart, 59.3 +/- 7.2, and liver, 6.6 +/- 0.4, was also no t significantly different among groups. Fatty acid composition of the gastrocnemius muscle was not significantly different among groups. Fas ting glycogen levels in the liver, gastrocnemius muscle, and heart wer e 6.4 +/- 3.7, 13.2 +/- 2.3 and 6.8 +/- 1.9 mu mol/g in LFD, 21.2 +/- 5.1 (p<0.05 vs. LFD and OF), 10.4 +/- 1.8 and 5.9 +/- 1.1 mu mol/g in OR, and 36.3 +/- 4.8 (p<0.05 vs. LFD and OR), 10.2 +/- 2.3 and 5.3 +/- 2.1 mu mol/g in OP rats, respectively. Triglyceride levels were simil ar among groups in plasma, heart and gastrocnemius muscle, but were si gnificantly (p<0.05) higher in the liver of OP (15.5 +/- 1.9 mu mol/g) compared to OR (9.1 +/- 1.1 mu mol/g) and LFD (8.1 +/- 1.4 mu mol/g) rats. These data suggest that susceptibility to dietary obesity, in th is rodent model, cannot be explained by differences in tissue oxidativ e capacity or muscle fatty acid composition.