Simultaneous measurements of chylomicron lipolysis and remnant removal using a doubly labeled artificial lipid emulsion: studies in normolipidemic and hyperlipidemic subjects.

An artificial chylomicron-like lipid emulsion doubly labeled with tri[(N)3H]oleoylglycerol ([3H]TO) and cholesteryl [1-14C]oleate ([14C]CO) was infused intravenously into human subjects with the purpose of simultaneously measuring the plasma disappearance rates (residence time, RT) of [14C]CO, which represents solely the splanchnic organ uptake of the remnant chylomicron core, and of [3H]TO, which combines the remnant disappearance with the shedding off of chylomicron triglycerides by the action of lipoprotein lipase. Thus, the fraction of the particle triglyceride content that is removed before the remnant is taken up is expressed as a delipidation index (DI = 1 - RT of [3H]TO/RT of [14C]CO. The present procedure has an advantage over the use of chylomicrons labeled with retinyl ester or radioactive triglycerides alone that represent, respectively, the chylomicron remnant or the whole particle metabolism only. When normal subjects as well as primary hyperlipidemic subjects were studied, the plasma triglyceride concentration was directly related to [14C]CO RT and [3H]TO RT, but inversely related to the delipidation index. There may be different patterns of relations between these parameters of chylomicron metabolism in primary and in secondary hyperlipidemias, as well as under the action of drugs that influence the metabolism of lipoproteins.