Biosynthesis and Secretion of Plasma Glycoproteins on Galactosamine-treated Rats

Abstract

Hyperasialoglycoproteinemia is observed in galactosamine-treated rats. I studied the effects of galactosamine on biosynthesis and secretion of rat plasma glycoproteins in order to obtein the information on mechanism of hyperasialoglycoproteinemia. The administration of a large amount of galactosamine to rats resulted in marked elevation of values of GOT, GPT and serum asialoglycoproteins, and decrease of serum total protein and hepatic asialoglycoprotein receptor. The amount and rate of incorporation of leucine and mannose into plasmatransferin and total protein were inhibited by 85^-90% on first and third day after galactosamine injection. Amino acid incorporation into these proteins returned to normal on fifth days, in contrast, mannose incorporation remained 50% reduction of normal on fifth day. The ratio of high mannose type to compley type in carbohydrate chains of plasma glycoproteins of normal rats and those on fifth day after injection was 94.5: 5.5 and 97.5: 2.5, respectively. The ratio of N-acetylglucosamine tosialic acid of the former was as same asthat of the latter.
From these results, I concluded as follows.
1. Most of biosynthesis and secretio n of plasma glycoproteins stopped on first and third day after galactosamine injection.
2. On fifth day, partia l glycosylated plasma glycoproteins were observed in the circulatin, but their carbohydrate chains were processed normally.
Therefore, pathogenesis of hyperasialoglycopro teinemia in galactosamine hepatitis was not secretion of plasma glycoproteins with abnormal carbohydrate chains but decrease of asialoglycoprotein receptor in liver.