Diurnal changes and adaptation by the liver of hamsters to an
atherogenic diet.
Robins, Sander J., Joan M. Fasulo, Carole R. Pritzker, Jose M.
Ordovas, and George M. Patton.
Department of Medicine, Veterans Administration Medical Center and
Boston University School of Medicine, Boston, MA 02130, and USDA
-Human Nutrition Research Center on Aging at Tufts University, Boston,
MA 02111
APStracts 2:0189R, 1995.
Studies were performed in freely-feeding, male (F1B) Syrian hamsters
fed a high fat diet to determine the extent and manner of adaptation
of the liver to diurnal changes in eating patterns and an increase in
serum lipids. Serum cholesterol and triglycerides strongly paralleled
changes in food consumption and were 40-50% greater during the 12-h
dark period than the 12-h light period of the diurnal cycle. Hepatic
cholesterol changes closely approximated changes in serum cholesterol
(r = 0.916), due principally to changes in hepatic cholesteryl esters
that were on average about 10-fold greater with the high fat diet
than with a chow diet. With the high fat diet, hepatic cholesteryl
esters were, however, extremely variable and were 40% greater at the
mid-dark than at the mid-light period. With high fat there was also a
marked increase in the secretion of very-low-density lipoproteins
(VLDL) from the liver that were cholesteryl ester-rich and closely
paralled the diurnal changes in hepatic cholesteryl esters (r =
0.911). In contrast, although with a high fat diet biliary
cholesterol secretion was increased, the increase in cholesterol in
bile exhibited no diurnal pattern and with the high fat diet was far
less in magnitude than the increase of cholesterol in VLDL. Biliary
cholesterol secretion is dependent on bile acid secretion. However,
with the high fat diet, neither the bile acid pool size nor bile acid
secretion was increased compared to chow-fed controls. Moreover, with
high fat at mid-dark, bile acid secretion was significantly less than
controls at mid-dark. Thus, in these hamsters a high fat diet
produced a marked increase in serum cholesterol that was distinctly
diurnal and was compensated for by a diurnal increase in hepatic
cholesteryl ester stores and the secretion of cholesteryl esters in
VLDL. In contrast, cholesterol secretion in bile did not correspond
to the fluctuating changes of cholesterol in the liver and was far
less in magnitude than would be necessary to reduce a greatly
expanded pool of hepatic cholesterol.
Received 27 June 1995; accepted in final form 27 June 1995.
APS Manuscript Number R143-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.