Date of Award:

5-1979

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Animal, Dairy, and Veterinary Sciences

Department name when degree awarded

Interdepartmental Program in Toxicology

Committee Chair(s)

Joseph C. Street

Committee

Joseph C. Street

Abstract

This investigation addressed several aspects of the covalent interaction of metabolites of the insecticide chlordane with cellular macromolecules in vitro. Microsomal preparations from the liver of mice and rats were used and covalent binding to microsomal protein and RNA or to added calf thymus DNA was studied. Pure 14C-labelled cis- and trans-chlordane isomers as well as an isomeric mixture (14C-cis-chlordane plus 14C-trans-chlordane 3:1, w:w) were used as substrates for the in vitro system. Biochemical parameters investigated included inhibition of microsomal mixed-function oxidase and epoxide hydratase plus the induction of these enzymes by pretreatment with chlordane or phenobarbital. The effect of these manipulations on covalent binding of the metabolites to the macromolecules was of interest.

Isolation of the protein, RNA and DNA from the in vitro microsomal systems and determination of unextractable radioactivity indicated that the chlordane derived material bound to each of the macromolecules investigated. The only exception was that mouse liver microsomes did not activate trans-chlordane to a form which bound to DNA in measurable amounts under the conditions employed.

Microsomal epoxide hydratase and aminopyrine demethylase activity were increased in both the rat and the mouse following chlordane pretreatment. The effect of this induction on the macromolecular interaction of chlordane metabolites was variable for both chlordane and phenobarbital pretreated groups. Generally, for the mouse, induction increased binding to protein and DNA but decreased binding to RNA. In the rat, induction decreased binding to each of the macromolecular species. The effect of enzyme inhibition was variable in both species under the different conditions tested except for the binding of cis-chlordane derived material to DNA in the mouse liver system. In that case inhibition of epoxide hydratase clearly reduced the concentration of material covalently interacting with the DNA to unmeasurable levels.

The results indicated little possibility that the primary epoxide metabolite of chlordane, oxychlordane, is involved in the binding. The effects of epoxide hydratase inhibition, however, indicate that some secondary epoxide is involved in the cis-chlordane binding to DNA in the mouse. The possible analogy between the binding behavior of chlordane found in this study and the binding behavior of other well characterized toxic compounds is discussed.

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