Rat plasma triglycerides and hepatic fatty acid synthetase mRNA, but not apolipoprotein B and A-IV mRNA, respond to dietary fat content.

The objective was to determine whether apolipoprotein B and A-IV mRNA abundance or plasma lipid concentrations would be altered by chronic or acute consumption of diets that differed in fat content. Forty Wistar male rats were fed either a low fat (5 g/ 100 g) or high fat (20 g/100 g) diet for 4 wk. Animals were killed unfed or 3 h after consumption of a test meal of the diet to which they had been adapted (n = 8). In addition, a low fat diet-adapted group was fed a high fat test meal and killed 3 h after the meal. Adaptation to the high or low fat diets did not result in differences in triglyceride or cholesterol concentrations in the plasma of unfed rats. In fed animals, plasma, VLDL, and LDL triglyceride concentrations were significantly higher in those fed the high fat test meal than in those fed the low fat test meal. Feeding did not alter plasma cholesterol concentrations; however, LDL cholesterol concentrations in the groups fed the high fat meals were significantly higher than in the group fed the low fat meal. There were no differences in plasma apolipoproteins B, A-IV, E, and A-I nor in the liver or intestinal apolipoprotein B and A-IV mRNA contents. Fatty acid synthetase (FAS) activity was significantly higher in rats adapted to the low fat diet, and no increase in activity due to feeding was observed. Hepatic FAS mRNA was higher in fed than unfed rats, and the low fat test meal resulted in a higher level than the high fat test meal. Plasma lipid concentrations were affected by the fat content of test meals rather than by the adaptation diet fat content. Apolipoprotein B and A-IV mRNA do not seem to respond to dietary fat or meal feeding.