TIME-COURSE OF ADAPTATION TO A HIGH-FAT DIET IN OBESITY-RESISTANT ANDOBESITY-PRONE RATS

The purpose of the present study was to characterize the time course o f adaptation (i.e., circulating metabolites and hormones, fat pad mass , lipoprotein lipase) to a high-fat diet in obesity-prone (OF) and obe sity-resistant (OR) male Wistar rats. Delineation of OP and OR was bas ed on body weight gain (upper tertile for OF; lower tertile for OR) af ter 1 wk on a high-fat diet (60% of kcal from corn oil). Rats were kil led after 1, 2, or 5 wk of the dietary period. Increased body weight a nd percent body fat in OP rats at 1 wk could not be accounted for by i ncreased retroperitoneal or epididymal fat pad weight. Plasma nonester ified fatty acids and triglycerides, as well as blood concentrations o f glucose, lactate, and glycerol, were similar throughout the study. P lasma insulin was significantly greater in OP vs. OR rats and low-fat diet (LFD; 20% of kcal from corn oil) controls at 5 wk only, and blood P-hydroxybutyrate (mM) was significantly higher in OR compared with O P and LFD rats at 1, 2, and 5 wk. Lipoprotein lipase mRNA and activity were significantly greater in epididymal fat pad and significantly lo wer in gastrocnemius muscle of OP vs. OR rats at 1 wk. Results suggest that early (i.e., 1 wk) differences in body weight and fat weight bet ween OP and OR rats are not due to fat deposition in retroperitoneal o r epididymal fat depots, and tissue-specific changes in LPL (increase in epididymal fat pad and decrease in gastrocnemius muscle) that occur in OP compared with OR rats after 1 wk on a high-fat diet provide a m etabolic environment favoring fat storage.