Differing uptake of emulsion triglyceride by the fed and fasted rat liver

The recycling perfusion of a fasted rat liver with an apoprotein E-enriched synthetic triglyceride emulsion revealed a significantly greater hepatic uptake of both the apoprotein and the triglyceride than did the liver of a chow-fed animal. This greater hepatic triglyceride uptake by the perfused fasted liver in comparison to the fed was also noted for emulsions containing no added apoprotein or supplemented with both the E and CIII-1 proteins. However, no difference in the uptake of the triglyceride emulsion was seen for the fed and fasted livers when evaluated by a nonrecycling single pass perfusion. The isolated hepatocyte plasma membranes from fasted rats failed to demonstrate enhanced binding of apoprotein or lipid when compared to those from fed animals. If the residual E loaded triglyceride emulsion was recovered from the recycling perfusates of fed and fasted livers and evaluated in a non-recycling single-pass system, the emulsion from the fasted perfusion was cleared as facilely as previously, whereas that from the fed was less actively cleared. The emulsions retrieved from the perfusion of the fed liver contained significantly more protein than did the fasted; in particular apo C. This apparent alteration of emulsion apoproteins by the fed liver possibly results in a less active hepatic retrieval and may be important in downregulating the entry of lipoprotein triglyceride in the postabsorptive liver.