Origin of intestinal lymph cholesterol in rats: contribution from luminal absorption, mucosal synthesis and filtration from plasma.

Measurement of cholesterol transport from plasma to intestinal lymph based on i.v. labeling with radioactive beta-sitosterol was validated by the simultaneous i.v. administration of 4-14C-beta-sitosterol and of 1,2-3H-cholesterol to two rats with bile duct, intestinal lymph, duodenum and jugular vein cannulations. In 11 other rats undergoing intestinal lymph duct cannulation, each potential source of lymph cholesterol was determined 2-3 weeks after i.v. pulse administration of 1,2-3H-beta-sitosterol and 4-14C-cholesterol. For this purpose, lymph fat, after an intragastric infusion of cottonseed oil (1900mg), was used as a marker for total cholesterol mass transported into intestinal lymph. In these two experimental groups of rats, namely, in the absence and in the presence of supplemental dietary cholesterol, filtration of cholesterol from plasma to lymph and absorption of cholesterol derived from bile did not change in the presence of exogenous cholesterol. In other words, absorption of cholesterol based on the amount of cholesterol in intestinal lymph by direct measurement was comparable to the level obtained by the isotopic procedure based upon lowering of the lymph/plasma ratio of 4-14C-cholesterol specific activity (d.p.m./mg of cholesterol). Plasma cholesterol appearing in intestinal lymph was transported mainly in lymph lipoproteins at a density below 1.006 (i.e., chylomicrons). Esterification was not necessary for luminal cholesterol absorption under these experimental conditions.