Very low density lipoproteins in intestinal lymph: role in triglyceride and cholesterol transport during fat absorption

Abstract

A B S T R A C T The role of nonchylomicron very low density lipoproteins (VLDL, in the transport of triglyceride and cholesterol was studied during lipid absorption. Various long chain fatty acids were infused intraduodenally in the form of mixed fatty acid-monoolein-taurocholate micelles; control animals received saline or taurocholate.As compared with controls, all fatty acids (palmitic, oleic, linoleic) resulted in significant increases in chylomicron (Sf > 400) triglyceride. In addition, palmitic acid resulted in a twofold increase in VLDL triglyceride, whereas with the absorption of oleic or linoleic acid VLDL triglyceride did not change significantly. Differences in triglyceride fatty acid composition between chylomicrons and VLDL were observed during lipid absorption.Although the absolute amount of endogenous choles- These studies demonstrate that dietary long chain fatty acids differ significantly in their effects upon the transport of triglyceride and cholesterol by lipoproteins of rat intestinal lymph. These findings, together with the observed differences in rates of removal of chylomicrons and VLDL from plasma, suggest that variations in lipoprotein production at the intestinal level may be reflected in differences in the subsequent metabolism of absorbed dietary and endogenous lipids. INTRODUCTIONIn previous studies (1) we have shown that in the fasting state very low density lipoproteins (VLDL) play a major role in the transport of endogenous lipids in intestinal lymph. This class of triglyceride-rich lipoproteins can be operationally distinguished from the less dense chylomicrons by its flotation rate (VLDL, Sf 20-400; chylomicrons, Sf > 400). Although it is possible that VLDL and the more often studied chylomicrons represent two ends of a single spectrum of particle size and density, these two fractions differ also in other respects, including electrophoretic mobility in agarose gel and per cent lipid and protein composition (1, 2). Accordingly, intestinal lymph VLDL bear a greater similarity to plasma VLDL than to chylomicrons. These observations have suggested that the metabolic role of in-

Metabolism of cholesterol-rich chylomicroms. Mechanism of binding and uptake of cholesteryl esters by the vascular bed of the perfused rat heart.

“…Each point represents the mean of duplicate determinations. Minutes After Infusion FIGURE 11 Clearance of chylomicron cholesteryl [ 20 mg/h of triglyceride (22). Thus, lymphatic particles under these conditions will contain an average cholesteryl ester/triglyceride weight ratio of 0.03.…”

Cholesterol: from feeding to gene regulation

“…Caco-2 cells) have been used extensively to study the formation and the secretion of lipoproteins [49,54,55,74,113] and the genetic expression and posttranslational modification of apolipoproteins [75]. During fasting, very low-density lipoproteins (VLDLs) are the only lipoproteins produced by the small intestine [87,88,114]. Following a meal, the small intestine produces predominantly CMs [114,135].…”

A possible role for rat intestinal surfactant-like particles in transepithelial triacylglycerol transport.

“…There is evidence that chylomicrons and VLDL are packaged differently within the enterocyte (3,11,12). The difference in intercellular lipid packaging has been reinforced by experiments using the nonionic hydrophobic surfactant, Pluronic L-8 1. This compound, when given intraluminally by continuous infusion or by bolus injection, caused a decrease in chylomicron formation and transport (13).…”