ETHANOL EFFECTS ON HEPATIC PROTEIN TURNOVER

Excessive ethanol consumption causes an increase in liver protein content.
The studies proposed are designed to ascertain the mechanism of this
increase by examining intracellular protein turnover rate changes that
occur during chronic ethanol consumption. The proposed hypothesis is that
chronic ethanol ingestion causes a decrease in the rate of degradation of
intracellular hepatic proteins which results in their net accumulation in
the liver. The proposed experiments will examine protein synthesis in some
detail, but greater emphasis will be given to protein catabolism in the
alcoholic animal. The initial objective is to determine the time course of
alcohol-induced protein accumulation in livers of rats maintained on a
liquid diet containing ethanol. One of two control groups of rats will be
pair-fed an identical liquid diet minus ethanol. The second control group
will receive a normal (chow) diet. These initial studies will determine
the progression of protein accumulation, and the time at which an
ethanol-induced 'steady state' of hepatic protein is reached following
initiation of ethanol feeding. Protein turnover measurements under both
nonsteady state and steady state conditions will then be conducted on total
liver and specific subcellular fractions from control and ethanol fed
rats. Quantitative immunochemical techniques will also measure turnover
rates or specific intracellular proteins. Measurements of in vivo, protein
synthesis and degradation will utilize single and dual isotope
pulse-labelling techniques. Protein synthesis will be measured by
incorporation of [3H]puromycin into nascent polypeptides. Protein
catabolism studies during hepatic protein increase (nonsteady state) will
examine the kinetics of decay of isotopically prelabelled intracellular
proteins. Turnover measurements, conducted under steady state conditions,
will utilize dual isotope measurements to further examine differential
turnover rate changes in subcellular fractions in the alcoholic state. The
proposed studies will provide information on changes in rates of hepatic
intracellular protein turnover during ethanol ingestion. They will also
allow correlations with, and will serve as a useful prototype for similar
studies with other hepatotoxins. Protein accumulation in the liver may
contribute to ethanol-induced liver injury since it is associated with
hepatomegaly, a common state in the development of alcoholic liver disease.