Alpha-tocopherol is secreted from rat liver in very low density lipoproteins.
Three separate studies were carried out to test the hypothesis that rat liver secretes vitamin E (alpha-tocopherol) within very low density lipoproteins (VLDL). i) When the clearance of plasma chylomicrons (CM) and VLDL was blocked by the administration of Triton WR-1339, alpha-tocopherol concentrations increased linearly with time in both classes of triacylglycerol-rich lipoproteins, although accumulation rates within VLDL exceeded those within CM. For fasted rats, appearance of alpha-tocopherol in VLDL persisted at slightly reduced rates. alpha-Tocopherol and triglycerides in the VLDL fraction responded to Triton WR-1339 administration by coordinate increases. In contrast to the situation in serum, alpha-tocopherol concentrations decreased in the liver following injection of Triton. ii) In order to inhibit the secretion of hepatic lipoproteins containing apolipoprotein B (apoB), rats were fed a diet containing orotic acid. This resulted in a reduction of apoB and alpha-tocopherol concentrations in serum and VLDL, whereas the vitamin E content of liver was increased. iii) In primary cultures of hepatocytes, alpha-tocopherol was secreted into the culture media predominantly within VLDL. We, therefore, conclude that the liver secretes alpha-tocopherol within VLDL and in this way contributes to the maintenance of serum vitamin E concentrations.
Cohn
W
W
Department of Vitamin Research, F. Hoffmann-La Roche & Co., Ltd., Basle, Switzerland.
Loechleiter
F
F
Weber
F
F
D000818:Animals; D001055:Apolipoproteins B / Q000032:analysis; D002478:Cells, Cultured; D002914:Chylomicrons / Q000378:metabolism; D003470:Culture Media / Q000032:analysis; D008079:Lipoproteins, VLDL / Q000097:blood / Q000378:metabolism*; D008099:Liver / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009963:Orotic Acid / Q000494:pharmacology; D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D014810:Vitamin E / Q000097:blood / Q000378:metabolism*
D001055:Apolipoproteins B; D002914:Chylomicrons; D003470:Culture Media; D008079:Lipoproteins, VLDL; D014810:Vitamin E; D011092:Polyethylene Glycols; D009963:Orotic Acid; C016811:tyloxapol