Covalent binding of trans-stilbene to rat liver microsomes.

A number of estrogenic compounds have been shown to bind covalently to tissue macromolecules. Some of these agents cause impairement of liver function as measured by bromosulfophthalein clearance time. Trans-stilbene, a weak synthetic estrogen, which has been shown to be hydroxylated in several animal species, was investigated to determine if it covalently binds to tissue macromolecules. Liver damage was also evaluated histopathologically. Trans-stilbene binds covalently in vivo to various tissues of non-pretreated, phenobarbital-pretreated and 3-methylcholanthrene-pretreated rats. Pretreatment with 3-methylcholanthrene caused the greatest amounts of ¹⁴C-trans-stilbene to covalently bind to plasma and liver proteins. Studies in vitro showed that ¹⁴C-trans-stilbene became covalently bound to hepatic microsomes and that the covalent binding of ¹⁴C-trans-stilbene to liver microsomes from non-pretreated, phenobarbital-pretreated and 3-methylcholanthrene-pretreated rats was linear with time for at least 20 min. Oxygen and NADPH were necessary for binding. Carbon monoxide inhibited covalent binding to microsomes from non-pretreated rats and, to a much lesser extent, to microsomes from 3-methylcholanthrene-pretreated rats. The effects of various pretreatments on the covalent binding in vitro paralleled those of the binding in vivo. Although trans-stilbene was seen to bind covalently in vivo and in vitro, no histopathological abnormalities of liver or kidney were observed. Pretreatment of rats with phenobarbital or 3-methylcholanthrene, before administration of trans-stilbene, also did not cause any tissue abnormalities in liver or kidney. Glutathione did not seem to act as a protective agent in this study because, even after complete depletion of this substance, trans-stilbene did not cause any significant liver or kidney histopathological changes.