Serum Lipids After Intravenous and Intragastric Fat Emulsion in Man

Abstract

1. For the purpose of studying some mechanisms of lipid transport, the effect of fat emulsion on whole serum and subnatant serum lipids after single intragastric and intravenous administration and after daily intravenous infusion was studied in healthy young adults. 2. The level of whole serum neutral fat after intragastric administration of fat in the same subject did not result in as great an increase as was observed after intravenous administration. Following a single intravenous infusion of fat emulsion, subnatant serum neutral fat and free cholesterol reached a maximum eight hours after the start of the infusion. Increases were observed after intragastric administration of fat emulsion but not to the same degree as after intravenous infusions. During the first day, cholesterol and phospholipids decreased substatially in whole serum and subnatant after both intragastric and intravenous administration of fat emulsion, but returned to preinfusion levels on the second day of the experiment when no fat load was administered. 3. Daily intravenous administration of fat emulsion resulted in essentially similar patterns on the three days studied. Neutral fat and phospholipids peaked at the end of the infusion in the whole serum, and on successive days, the clearing rate of the infused fat emulsion decreased and the fasting level for neutral fat increased. Neutral fat in the subnatant serum reached its highest level four hours postinfusion along with an increase in cholesterol. The esterified cholesterol fraction dropped in serum from the beginning of the experiment and fell to its lowest point by the end of the third day, gradually returning to preinfusion levels by the sixth day. 4. The results of this study strongly suggest that the infused artificial chylomicrons are removed from the circulation essentially intact, reappearing, at least in part, as “soluble” lipoprotein. Serum cholesterol apparently becomes associated with the infused neutral fat thereby accounting for the immediate decrease in serum cholesterol. 5. The experiments described are discussed in the light of current knowledge in lipid transport.