The liver has a major role in the metabolism of cholesterol, being
the main site of lipoprotein assembly and degradation and the only
tissue where the metabolism of cholesterol to bile acids occurs.
This provides the major pathway for the removal of cholesterol from
The results described in this thesis concern the use of specific
enzyme inhibitors (58-035, Azacholesterol, Mevinolin) to determine
the intracellular use of different sources of cholesterol in
monolayers of rat hepatocytes. In particular, the fates of newly
synthesized cholesterol from mevalonic acid and cholesterol derived
from HDL2 were investigated.
Incubation of hepatocyte monolayers with 58-035 resulted in the
inhibition of esterification. In the presence of mevalonic acid as
a cholesterol source, 58-035 stimulated bile acid synthesis.
Azacholesterol inhibited bile acid synthesis, had no effect on
cholesterol synthesis, and in the presence of mevalonic acid,
stimulated secretion of cholesterol by the hepatocytes; it had no
effect on cholesterol esterification. Mevinolin inhibited
cholesterol synthesis and as a result inhibited esterification.
HDL2, in the presence of mevinolin, was used as a cholesterol
source. It stimulated bile acid synthesis and cholesterol
esterification. Addition of 58-035 to the system resulted in the
inhibition of both esterification and bile acid synthesis. Overall,
the results indicated that different intracllular pools of free
cholesterol exist and that the inter-relationships of these pools
give a complex pattern of flux of intracellular cholesterol between
various pathways in the rat hepatocyte.