The effect of ethanol on liver glycogen of fed animals : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biochemistry at Massey University
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Date
1996
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Massey University
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Abstract
A hyperglycemic effect of ethanol has been reported in fed animals, but
is poorly documented and in general, little work has been done on the
effects of ethanol on carbohydrate metabolism in the fed state. This
study is a further extension of research investigating the effect of ethanol
on liver carbohydrate metabolism, as liver is a major source of glucose
output in fed animals. It has been suggested that the hyperglycemic
condition might be caused by an ethanol-stimulated liver glycogenolysis.
Because it was possible that the actions of ethanol were a direct effect
on carbohydrate stores rather than an effect mediated by h01mones,
ethanol was tested on a simple unicellular organism Ochromonas danica
where hormonal mechanisms are absent. It appears that ethanol does
cause a reduction of Ochromonas carbohydrate stores in the absence of
hormones. The major difficulty in using this organism was that its
carbohydrate content could change according to the osmotic pressure in
the external environment which therefore had to be strictly controlled.
Fallowing the initial work using Ochromonas danica, further
experiments were carried out using fed rats to assess the effects of
ethanol on tissue glycogen stores. Sprague-Dawley rats were
administered with an acute dose of ethanol (6g/kg). The effect of ethanol
on the liver glycogen content of the animals was examined at 45, 90 and
180 minutes after the dose given. It appears that ethanol would lead to a
significant decrease in liver glycogen content in both male and female
rats at any given time. However, the decrease was not as much as that
reported in the literature. Presumably this is due to the differences in
ethanol administration, assays of liver glycogen and the strains of
animals used in the experiment. The glycogen content in other tissues
such as heart, kidney and muscle was also investigated but little
difference was observed with ethanol treatment except in muscle, which
showed some increase in glycogen content especially in the males. It is
interesting that the free glucose concentrations in these tissues were not
elevated as might have been expected if liver glycogen breakdown had
occurred. Moreover, ATP levels were also observed to be unchanged.
The female rats were found to metabolise ethanol at a slower rate than
males. The ethanol concentration in their extrahepatic tissues was
similar to the calculated theoretical value for initial ethanol absorption.
However in male rats, it is lower than the theoretical value. This
indicates that the ethanol clearance curve for these tissues was not
linear, and this implies that other factors such as delayed absorption or a
first-pass effect (Lieber et al., 1994) might occur.