Graduate Thesis Or Dissertation
 

Mechanisms affecting the bioaccumulation of dietary quinoline by rainbow trout (Salmo gairdneri)

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  • Factors that influenced the uptake, storage, and elimination of dietary quinoline by rainbow trout (Salmo gairdneri) were studied to obtain an understanding of the mechanisms affecting the bioaccumulation of dietary contaminants in teleosts. Rainbow trout readily absorbed ¹⁴C-quinoline from pelleted food (1% ration at 138 ug quinoline/g food) and most tissues reached apparent steady-state after 10 days feeding. Maximum whole-body concentrations of quinoline plus metabolites were only 30 ng/g after 7 days depuration. Uptake rate constants ranged from 0.00006/day for muscle to 0.1455/day for gallbladder plus bile. Mean elimination half-life for quinoline-derived radioactivity ranged from 0.4 days in gills to 8.7 days for muscle. Depending on tissue, 58-83% of the stored radioactivity was present as metabolites. About 14% of the radioactivity in the bile was present as glucuronide conjugates. Quinoline was absorbed from the stomach by rainbow trout and peak serum levels occurred 4-8 hr after a single feeding. Pharmacokinetics were described using a two-compartment body model with first-order absorption and disposition; estimated half-lives for the a and B phase were 4.1 and 54.1 hr, respectively. Depending on dose, 71 to 83% of the ingested radioactivity was excreted during the first 24 hr after feeding. Branchial excretion was the primary route of excretion, all other routes (fecal, biliary, urinary, dermal) contributing <5% of the eliminated dose within 48 hr after ingestion. There was evidence for saturation of minor excretory pathways as the dose was increased from 1 to 100 mg quinoline/kg body weight. Apparent spillover into the branchial route occurred at the 100 mg/kg dose. Quinoline was eliminated across the gills as parent compound; no peaks representing individual polar metabolites were detected. Physiological processes associated with feeding and digestion influenced the absorption and fate of dietary quinoline. The pH of the gut environment affected the availability of quinoline and potential for transfer across tissue membranes. Acidic gastric secretions were initially buffered by the food bolus, affecting the degree of ionization of parent compound. In the more alkaline intestine. >99% of quinoline was available for absorption. About 60% of the residual body burden was stored in the gallbladder bile, but bile was retained only in starved fish. There was no evidence for enterohepatic circulation of quinoline or its metabolites following ejection of gallbladder bile. Increased feeding rates enhanced the movement of the food bolus and associated radioactivity through the intestine, but did not affect patterns of tissue disposition.
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