The effects of ethanol and its metabolites on glycoprotein secretion were investigated in rat liver slices. A pulse-chase system was used to study the influence of these agents on glycoprotein secretion independently of their effects on synthesis. When ethanol (10 mM) was present in the incubation medium, the secretion of [14C]leucine- and [14C]glucosamine-prelabeled proteins into the medium was inhibited. The secretion of glycoproteins, that were prelabeled in the terminal positions of the oligosaccharide side chain with [14C]fucose or [14C]galactose, was also inhibited by ethanol. When low concentrations of acetaldehyde, similar to levels generated during in vivo ethanol oxidation, were maintained in the medium by infusion, the secretion of [14C]leucine-, [14C]glucosamine- and [14C]fucoseprelabeled glycoproteins was impaired. Acetate (1 and 5 mM) did not affect the secretion of prelabeled glycoproteins. Colchicine (50 μM), an agent known to block the secretion of completed glycoproteins, behaved in a manner similar to ethanol in inhibiting the secretion of glycoproteins in our system. These results indicate that ethanol via its metabolite, acetaldehyde, impairs the secretion of glycoproteins by the liver and suggest that this impairment follows the attachment of the terminal monosaccharides in the Golgi membrane.
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