CHARACTERIZATION OF THE FIBROTIC LESION IN DIBUTYLTIN-INDUCED EXPERIMENTAL LIVER INJURY

Author

Jeannee Karen Yermakoff, University of Rhode Island

Date of Award

1980

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Pharmaceutical Sciences

Department

Interdepartmental Program

First Advisor

George C. Fuller

Abstract

Administration of di-n-butyltin dichloride (DBT) by oral intubation has been shown to produce hepatic fibrosis in rats. Unlike post-necrotic experimental fibrosis, DBT-induced hepatic fibrosis progresses from inflammation and biliary injury. The relationship of histological changes to various parameters of collagen synthesis and liver injury were investigated. In vitro collagen synthesis was determined by incubation of liver biopsies with labeled praline and subsequent digestion with protease-free collagenase. Prolyl hydroxylase activity in liver homogenates was taken as a second parameter reflecting the rate of collagen synthesis. DBT administration (20 mg/kg/day, p.o.) produced a progressive increase in both in vitro collagen synthesis and prolyl hydroxylase activity from 0 to 4 days. The increases in these two parameters were significantly correlated and both accompanied the appearance of inflammatory cells in portal tracts and bile duct proliferation. Serum alanine transaminase activity was increased after 4 days of DBT administration. DBT administration (20 mg/kg, q.o.d., p.o.) for 12 days produced increased prolyl hydroxylase activity, an increase in the percent of in vitro collagen synthesis, and the accumulation of hydroxypraline in the liver. These biochemical changes were associated with fibrosis, bile duct proliferation and extensive inflammation in the portal tracts. Alanine transaminase and alkaline phosphatase activities in serum were unchanged after 12 days of DBT treatment. Rats 4 weeks of age at the start of treatment were relatively resistant to the effects of DBT (20 mg/kg, q.o.d., p.o.) administered for 12 days. Prolyl hydroxylase activity in these 4-week old rats was 125% of control compared to 150% and 215% in the 9- and 14-week old groups, respectively. Leucocytosis and weight loss usually associated with DBT-induced liver injury were absent in these younger rats and histology was similar to that of control animals. Thymus atrophy was observed in the 4-week old rats. Investigation of lymphocyte-mediated cytotoxicity, delayed type hypersensitivity, and immunofluorescence in rats 9 weeks of age at the start of treatment failed to reveal an immunologic reaction against DBT or liver. The relationship of differences in hepatic microsomal metabolism to the age-related phenomena was investigated using an inhibitor of microsomal enzymes, SKF 525A. Administration of SKF 525A (50 mg/kg, b.i.d., p.o.) concomitantly with DBT (20 mg/kg/day, p.o.) resulted in an interaction between these two compounds with respect to their effect on prolyl hydroxylase activity. The elevation in serum alanine transaminase activity seen with DBT treatment alone after 4 days was completely prevented by the simultaneous administration of SKF 525A. Periportal inflammation and biliary changes were absent in rats receiving DBT and SKF 525A.