Apolipoprotein A-IV synthesis in rat intestine: Regulation by dietary triglyceride

Apolipoprotein A-IV (apoA-IV) synthesis rates were measured in vivo in rat enterocytes by immunoprecipitation after administration of [³H]leucine into in situ loops of jejunum and ileum. Basal apoA-IV synthesis rates (percent total protein synthesis) were significantly higher in jejunal enterocytes (2.05 ± 0.54%) compared with ileal enterocytes (0.48 ± 0.32%) from the same fasted animals. After an acute triglyceride bolus, significant and sustained elevations of apoA-IV synthesis rates were seen in both jejunal and ileal enterocytes with maximal effects noted at 4-6 h. Animals fed diets containing 30% wt/wt triglyceride as saturated (SF) or polyunsaturated (UF) fats for 6 wk had similarly increased rates of apoA-IV synthesis in jejunal enterocytes with both SF (3.73 ± 0.83%) and UF (3.33 ± 0.64%) but no change in ileal enterocytes. By contrast, animals consuming a fat-free diet for 3 wk had jejunal apoA-IV synthesis rates indistinguishable from basal values (2.40 ± 0.45%). Translatable intestinal mRNA levels for pre-apoA-IV after triglyceride increased in parallel to synthesis rates with a 50% increase in jejunum and a 350% increase in ileum observed at 4-6 h. These results suggest that apoA-IV synthesis by rat small intestine 1) increases in response to acute and chronic dietary triglyceride, 2) is maintained in the absence of dietary triglyceride, and 3) may be under pretranslational control.