Chronic dieldrin exposure increases hepatic disposition and biliary excretion of [14C]dieldrin in rainbow trout

Previous work demonstrated that exposure of laboratory animals including fish to certain organochlorine (OC) insecticides altered the tissue distribution of a subsequent tracer dose of the same [14C]OC. In the present study, 10- to 20-g rainbow trout were exposed to 15 ppm dieldrin in the diet. Fish were subsequently challenged at 2-week intervals with an intraperitoneal injection of 0.1 mg/kg [14C]dieldrin and viscera (liver, bile, mesenteric fat, kidney, and intestine) analyzed for radioactivity, 24 hr later. After 10 and 12 weeks of dieldrin pretreatment, [14C]dieldrin was significantly elevated relative to controls in liver (200%), bile (500%), and fat (500 and 1200% for 10 and 12 weeks, respectively) of pretreated fish. Other tissues were unchanged. Chloroform/methanol extractions revealed a time-dependent increase in label disposition to carcass lipid in controls but not in pretreated fish. Altered disposition could not be explained by changes in total body lipid or induction of total cytochrome P-450 or ethoxyresorufin-O-deethylase, pentoxyresorufin-O-deethylase, glutathione S-transferase, or UDP glucuronosyltransferase activities. In vivo assessment of [14C]dieldrin metabolism revealed no increase in hepatic and only a slight (22%) increase in biliary polar:nonpolar concentration ratio after 9 weeks 20 ppm dieldrin pretreatment. Results suggest that constitutive changes in liver integral to dieldrin sequestration, transport, or excretion may be an adaptive response of trout to chronic OC exposure.