Measuring very low density lipoprotein-triglyceride kinetics in man in vivo: how different the various methods really are

Abstract

Purpose of review: The purpose of this article is to briefly outline the methods that are currently available for the determination of very low density lipoprotein-triglyceride (VLDL-TG) kinetics in man in vivo.

Recent findings: A number of novel methodologies have been developed over the years for quantifying VLDL-TG production, clearance, and turnover rates. Besides the splanchnic arteriovenous balance technique, tracer methods with radioactive and, more recently, stable isotopes have been widely used. Most of the latter approaches utilize an isotopically labelled substrate, such as glycerol, fatty acid or acetate, which is eventually incorporated into a VLDL-TG moiety, and monitor the time course of change in specific activity or enrichment. A procedure of in vivo labelling of VLDL-TG with stable isotopes and use of the labelled VLDL-TG as a tracer has also been described in man. There is, however, considerable variability in estimates of VLDL-TG kinetics obtained by the various techniques, which cannot be readily attributed to normal physiological variation. Still, a large part of this discrepancy may be related to differences in VLDL-TG pool size within the normal range, which seem to account for approximately 40-50% of the total variance in VLDL-TG kinetics in both men and women.

Summary: Several methods are available for quantifying VLDL-TG kinetics in man in vivo, varying in the selection of tracer, mode of administration and sampling, and data analysis. These inherent features, along with different pool sizes, result in multifold variable estimations of VLDL-TG kinetic parameters.