SERUM TRIIODOTHYRONINE CONCENTRATION AND NA-ATPASE ACTIVITY IN LIVER AND SKELETAL-MUSCLE ARE INFLUENCED BY DIETARY-FAT TYPE IN RATS(,K+)

It has been shown previously that dietary fat type influences body fat accumulation in rats. The effects of dietary fat type on serum thyroi d hormone, activity of Na+,K+-ATPase and lipoprotein lipase were studi ed. Rats were fed an experimental diet containing lard, high oleic saf flower oil, safflower oil or linseed oil for 12 wk. Carcass fat conten t was significantly higher in rats fed the lard diet than in those fed the other diets. However, intra-abdominal adipose tissue weights were not affected by type of dietary fat. The serum triiodothyronine conce ntration and the activity of Na+,K+-ATPase in the liver and skeletal m uscle were significantly lower in the lard diet group than in the othe r diet groups. The lipoprotein lipase activity of abdominal subcutaneo us fat was significantly higher in rats fed the lard diet than in rats fed the other diets, but the activity of lipoprotein lipase in intra- abdominal fat was not significantly different. These results suggest t hat the intake of lard, compared with the intake of the vegetable oils , may decrease Na+,K+-ATPase activity in the liver and skeletal muscle by lowering serum triiodothyronine concentration, resulting in the pr omotion of body fat accumulation.