Regulation by nutritional status of lipids and apolipoproteins A-I, A-II, and A-IV in inbred mice.

This study illustrates that genetic strain and feeding status can markedly influence tissue lipid concentrations and mRNA levels of apolipoprotein genes. C57BL/6 and BALB/c mice were maintained for 2 weeks on four test diets differing in amount of cholesterol and type of fat, and fasted for 4 h or 16 h prior to collection of tissues. For both strains, the primary effect of fasting from 4 h to 16 h was to paradoxically elevate triglyceride levels in plasma and liver, and to elevate hepatic apoA-IV mRNA levels. Triglyceride secretion rates, estimated after the injection of Triton WR-1339, suggested that elevations in plasma triglyceride levels were due to reduced clearance of very low density lipoproteins. Although plasma glucose levels decreased with fasting time for both strains, insulin levels decreased for BALB/c but not C57BL/6 mice regardless of diet. This suggests that factors thought to be mediated by insulin, (e.g., plasma free fatty acid concentrations; hepatic apoA-IV mRNA levels) may be influenced by local changes in insulin sensitivity, which are controlled genetically and are not reflected by plasma insulin levels. In summary, nutritional status influences a constellation of factors involved in lipid transport that also show strong genetic components and may influence subsequent analyses of gene expression in the mouse system.