Assessment of biliary mutagenicity in fasted rats given the known hepatotoxin 1,1-dichloroethylene

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These studies were conducted to determine the effect of a 200 mg/kg oral dose of 1,1-dichloroethylene (DCE) on the excretion of mutagenic bile by fasted rats and the effect of Aroclor 1254 pretreatment on the excretion of mutagenic bile in the standard Ames Salmonella/microsome mutagenicity assay. Aroclor 1254 pretreatment consisted of daily feedings of 150[micrograms]M/kg body weight one week (7 days) prior to surgery and treatment. On the eighth day rats were anesthetized with ethyl ether, a midventral incision made, and the bile duct cannulated with PE-10 tubing. The cannula was then secured with 2-3 sutures, exteriorized through the back of the animal, and placed in a foil covered microcentrifuge tube taped to the animal's flank. The incision was then closed with stainless steel staples and the animal transferred to an individual metabolism cage. After a 1-1.5 hour recovery period during which control bile was collected, the animals were given a 200 mg/kg oral dose of DCE. Bile was collected 1, 2, 3 and 4 hours after treatment and frozen until needed for mutagenicity testing. Bile from corn oil pretreated-mineral oil treated, corn oil pretreated-DCE treated, Aroclor 1254 pretreated-mineral oil treated, and Aroclor 1254 pretreated-DCE treated rats was then analyzed in Ames Salmonella typhimurium strains TA 97, TA 98 and TA 100. All samples were examined in the presence and in the absence of a previously induced population of rat liver microsomes and added cofactors (S9 mix). Analysis of bile-mediated reversion frequencies indicated that bile from all four groups of rats was non-mutagenic in the standard plate incorporation assay. Addition of S9 mix had no effect on mutagenicity of these samples. A pilot study confirming DCE-mediated hepatotoxicity and Aroclor 1254 protection from the hepatotoxic effect was also conducted. In this study, the extent of DCE-mediated hepatotoxicity and Aroclor 1254 protection from this hepatotoxic effect was similar to that recorded by Reynolds et al. (1975). Serum activities of SCOT, SGPT and LDH measured in the corn oil pretreated-DCE treated group were 32, 25, and 92 times greater than in the corn oil pretreated- mineral oil treated group respectively, while the Aroclor 1254 pretreated-DCE treated group was not significantly different from the corn oil pretreated- mineral oil treated control group. Hematoxylin and eosin stained hepatic tissue also confirmed DCE hepatotoxicity and Aroclor 1254 protection. Ames analysis of thiodiglycolic acid and chloroacetic acid, two known DCE metabolites, was also conducted and both compounds were found to be non- mutagenic at concentrations of up to 1000 [micro]g/plate whether or not S9 mix was present. [...]

Mutagenicity testing, Bile, Rats--Physiology, Animal testing