Journal of Lipid Research, Vol. 20, 494-502, May 1979
Copyright © 1979 by Lipid Research, Inc.

Apoprotein composition and turnover in rat intestinal lymph during steady-state triglyceride absorption

Peter R. Holt , Ai-Lien Wu , and Susanne Bennett Clark

Gastroenterology Division, Medical Service, St. Luke's Hospital Center, and College of Physicians and Surgeons, Columbia University, New York, NY

Apoproteins of chylomicrons, very low density lipoprotein (VLDL), and a low density + high density fraction secreted by proximal and distal rat small intestine into mesenteric lymph were examined during triglyceride (TG) absorption. Apoprotein output and composition were determined and the turnover rates of labeled non-apoB (soluble) apoproteins in lipoprotein fractions were measured after an intraluminal [³H]leucine pulse during stable TG transport into lymph. The output of VLDL apoproteins exceeded that of chylomicrons during the absorption of 45 µmol of TG per hour. More [³H]leucine was incorporated into VLDL than into chylomicrons and the decay of newly synthesized VLDL apoproteins was more rapid than that of chylomicrons, in part due to higher concentrations of apoA-I and apoA-IV with a rapid turnover rate. Chylomicrons from proximal intestine contained more apoA-I and less C peptides than chylomicrons from distal intestine. Ninety percent of [³H]leucine incorporated into soluble apoproteins was in apoA-I and apoA-IV, but little apoARP was labeled. The turnover rate of apoA-I and apoA-IV differed significantly in the lymph lipoproteins examined. Although total C peptide labeling was small, evidence for intestinal apoC-II formation and differing patterns of apoC-III subunit labeling was obtained. [³H]Leucine incorporation and apoprotein turnover rates in lipoprotein secreted by proximal and distal intestine were similar. The different turnover rates of apoA-I and apoA-IV in individual lipoproteins suggest that these A apoproteins are synthesized independently in the intestine.—Holt, P. R., A-L. Wu, and S. Bennett Clark. Apoprotein composition and turnover in rat intestinal lymph during steady-state triglyceride absorption.

Supplementary key words lipoproteins • VLDL • HDL • chylomicrons • fat absorption

Submitted on January 26, 1978
Revised on September 15, 1978
Accepted on December 18, 1978

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