An electron microscopic study of endogenous very low density lipoprotein production in the intestine of rat and man.

Previous studies have shown that in the absence of dietary lipid, intestinal lymph contains endogenous very low density lipoproteins (VLDL) which are identical to those in plasma in size, flotation rate, composition, and electrophoretic mobility. In order to document that these particles are produced in the mucosa of the small intestine itself, electron microscopic studies of rat and human intestinal mucosa were carried out. Small intestinal absorptive cells from rats fasted and restrained for 48 hr were rich in osmiophilic particles of the size of VLDL (300-1000 A). These particles were present in the endoplasmic reticulum and Golgi apparatus, and in intercellular spaces and lacteals; they were most abundant in mucosa from mid-jejunum. Similar particles were seen in jejunal mucosal biopsy specimens obtained from normal human volunteers after a 40-hr fast. After 6 hr of bile diversion or cholestyramine administration to fasted rats, the VLDL-sized particles virtually disappeared from the mucosa, suggesting that they were produced in the mucosa itself and depended upon the absorption of endogenous intralumenal lipid. These studies provide further evidence for the production of VLDL in absorptive cells of fasting rat and human intestine, and support the concept that the small intestine is a source of endogenous plasma VLDL.