Response of serum triglycerides of endogenous origin to the administration of triglyceride-rich lipid particles.

Studies were performed in rats to quantitate the changes in the concentration of serum triglycerides (TGs) of endogenous and exogenous origin after the acute intravenous injection of TG-rich emulsion particles. Emulsions were prepared to approximate chylomicrons and to contain a TG with a single fatty acid that could be traced during its clearance from the serum. After injection of emulsions, there was a rapid increase of not only the emulsion TG but TGs that contained a variety of other fatty acids of endogenous origin. Endogenous TGs were cleared from the serum at a slower rate than the emulsion TG and accounted for the major increase in serum TGs, especially during the latter phase of the clearance period. The increase in endogenous TGs was completely abolished by hepatectomy, which had no effect on the clearance of the emulsion TG. Results thus show that TGs of hepatic origin accumulate in the serum in response to the introduction of new TG-rich lipoproteins. Feeding rats a specific TG produced a similar result, with a pronounced rise in endogenous TGs that, like the changes after emulsion administration, was particularly evident once the TG that was fed was largely cleared from the serum. These findings are consistent with a process in which the preferential clearance of chylomicron TGs interrupts the clearance of very low density lipoprotein TGs that are produced by the liver. Consequently, the composition of serum TGs that accumulate after a meal may not reflect the composition of the meal itself.