Effects of ethanol on glycoprotein synthesis and secretion during inflammation-induced stimulation of hepatic glycoprotein secretion

Dean J. Tuma, Michael Floyd Sorrell

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Abstract

The effects of ethanol on glycoprotein metabolism in liver slices obtained from rats whose synthesis and secretion of glycoproteins had been stimulated by turpentine-induced inflammation were investigated and compared to colchicine, a potent inhibitor of secretion. Inflammation resulted in a large stimulation in liver slices of [14C]glucosamine and [14C]leucine incorporation into medium proteins and a lesser stimulation into hepatocellular proteins. Both ethanol (10 mm) and colchicine (50 μm), when present in the incubation medium, markedly decreased the appearance of glucosamine- and leucinelabeled proteins in the medium of both turpentine-stimulated and control livers. However, when microsomes were isolated and fractionated in a fraction rich in secretory contents and another rich in membrane components, the effects of these agents on the labeling of glycoproteins in these microsomal fractions differed. Colchicine did not affect the incorporation of either glucosamine or leucine into the membrane fraction but increased the labeling of the secretory fraction, whereas, ethanol decreased the labeling of both fractions. These effects were observed for both the stimulated and control slices. When protein synthesis was inhibited by cycloheximide in both types of slices, ethanol and colchicine decreased the secretion of glucosamine-labeled protein into the medium while increasing the specific activity of the glycoproteins of the secretory fraction without altering the labeling of the membrane fraction. When fucose, a terminal sugar, was used as a label, both agents decreased the secretion of fucose-labeled proteins into the medium while also causing a retention of labeled glycoproteins in the microsomal secretory fraction. These results indicate that the ethanol-induced inhibition of glycoprotein synthesis and secretion in the normal liver persists in the liver where synthesis and secretion have been greatly stimulated by inflammation.

Original languageEnglish (US)
Pages (from-to)303-311
Number of pages9
JournalToxicology and Applied Pharmacology
Volume63
Issue number2
DOIs
StatePublished - Jan 1 1982

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Glycoproteins
Ethanol
Liver
Glucosamine
Colchicine
Inflammation
Labeling
Turpentine
Proteins
Fucose
Membranes
Leucine
Cycloheximide
Microsomes
Metabolism
Sugars
Rats
Labels

ASJC Scopus subject areas

  • Toxicology
  • Pharmacology

Cite this

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abstract = "The effects of ethanol on glycoprotein metabolism in liver slices obtained from rats whose synthesis and secretion of glycoproteins had been stimulated by turpentine-induced inflammation were investigated and compared to colchicine, a potent inhibitor of secretion. Inflammation resulted in a large stimulation in liver slices of [14C]glucosamine and [14C]leucine incorporation into medium proteins and a lesser stimulation into hepatocellular proteins. Both ethanol (10 mm) and colchicine (50 μm), when present in the incubation medium, markedly decreased the appearance of glucosamine- and leucinelabeled proteins in the medium of both turpentine-stimulated and control livers. However, when microsomes were isolated and fractionated in a fraction rich in secretory contents and another rich in membrane components, the effects of these agents on the labeling of glycoproteins in these microsomal fractions differed. Colchicine did not affect the incorporation of either glucosamine or leucine into the membrane fraction but increased the labeling of the secretory fraction, whereas, ethanol decreased the labeling of both fractions. These effects were observed for both the stimulated and control slices. When protein synthesis was inhibited by cycloheximide in both types of slices, ethanol and colchicine decreased the secretion of glucosamine-labeled protein into the medium while increasing the specific activity of the glycoproteins of the secretory fraction without altering the labeling of the membrane fraction. When fucose, a terminal sugar, was used as a label, both agents decreased the secretion of fucose-labeled proteins into the medium while also causing a retention of labeled glycoproteins in the microsomal secretory fraction. These results indicate that the ethanol-induced inhibition of glycoprotein synthesis and secretion in the normal liver persists in the liver where synthesis and secretion have been greatly stimulated by inflammation.",
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