Bile diversion lowers apolipoprotein A-I and A-IV mRNA levels in rat ileum.

We recently reported that cholestyramine (a bile acid sequestrant) lowered ileal apolipoprotein A-I mRNA level in rats. To obtain further information about this phenomenon, in this study, we investigated whether bile diversion lowers apolipoprotein A-I mRNA level in the ileum of rats. Bile-diverted rats were fed a diet with no added Na taurocholate (control diet) or with 0.4% Na taurocholate for 7 days. Sham-operated rats were also fed the control diet for the same period. Northern blot analysis revealed that the relative concentrations of jejunal apolipoprotein A-I and A-IV mRNA at the end of experimental period did not differ between groups while ileal apolipoprotein A-I and A-IV mRNA concentrations were significantly lower in bile-diverted rats fed the control and Na taurocholate-containing diets than in sham-operated rats. Plasma total and HDL cholesterol concentrations were the same in all groups. Relative concentration of apolipoprotein A-I in plasma also did not change. These results suggest that the bile plays an important role in ileal apolipoprotein gene expression at the pretranslational stage, but it is still unclear whether the effector is the bile acid or not. The unchanged concentration of plasma apolipoprotein A-I may have resulted from the constant secretion independent of synthesis in the intestine or the larger contribution from the liver which is another principal site for apolipoprotein A-I expression.