American Journal of Clinical Nutrition, Vol 16, 173-181, Copyright © 1965 by The American Society for Clinical Nutrition, Inc.

Characterization of Lipids of Human Serum Following Intravenous Fat Infusion

¹ From the Southern Regional Research Laboratory, Southern Utilization Research and Development Division, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, Louisiana

Only small changes in amounts and electrophoretic mobilities of the various protein fractions were observed during the course of a single infusion of a fat emulsion. A rapid return to original values occurred 4 hours after completion of the infusion in all but one patient. In this patient a significant decrease in gamma globulin occurred, although an abnormal beta globulin distribution was noted. The effects of a single infusion on the protein fractions of human serum correspond to the effects observed on dog serum.

The mobilities of the lipoprotein fractions showed minor, but temporary, changes during the course of the infusions. As might be expected, the increase in total lipids extracted from samples of whole serum was greatest in those obtained at the completion of infusions. The extracted lipids, with a few exceptions, were of the same type and degree of unsaturation. The exceptions were noted in series 6-26 C.D. When chromatography was performed on whole serum samples, with no prior extraction of the lipids, separations indicated that some lipid-protein complex or lipoprotein did not move and the result was a lipid at the origin. The degree of unsaturation of the lipid at the origin and at the monoglyceride and diglyceride areas remained the same throughout the infusion, but at the free fatty acid and cholesterol fractions the lipid became progressively more unsaturated over the time intervals at which samples were drawn. The unsaturation of the triglycerides apparently increased until completion of the infusions, then decreased. Possibly, as was observed previously with samples of dog serum, prolonged administration of intravenous fat emulsions would result in more drastic changes in protein fractions, particularly a decrease in the albumin fractions, and a more lasting prealbumin lipoprotein fraction. However, no lasting effects were observed with the limited amount of lipid infusions used in this study. Since metabolism of lipids is intimately associated with that of carbohydrates and proteins, the findings of this and similar studies, which indicate alterations in protein and lipoproteins when fat is administered in the absence of proteins, should help to elucidate the mechanism of balance among these nutrients.