Journal of Lipid Research, Vol 29, 1359-1366, Copyright © 1988 by Lipid Research, Inc.
Alpha-tocopherol is secreted from rat liver in very low density lipoproteins
W Cohn, F Loechleiter and F Weber
Department of Vitamin Research, F. Hoffmann-La Roche & Co., Ltd., Basle, Switzerland.
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.