title: Gastrointestinal uptake and fate of cadmium in rainbow trout acclimated to sublethal dietary cadmium.
abstract: Adult rainbow trout were pre-exposed to a sublethal concentration of dietary Cd (500 mg/kg dry wt.) for 30 days to induce acclimation. A gastrointestinal dose of radiolabeled Cd (276 microg/kg wet wt.) was infused into the stomach of non-acclimated and Cd-acclimated trout through a stomach catheter. Repetitive blood samples over 24 h and terminal tissue samples were taken to investigate the gastrointestinal uptake, plasma clearance kinetics, and tissue distribution of Cd. Only a small fraction of the infused dose (non-acclimated: 2.4%; Cd-acclimated: 6.6%) was internalized across the gut wall, while most was bound in the gut tissues (10-24%) or remained in the lumen (16-33%) or lost from the fish (approximately 50%) over 24 h. Cadmium loading during pre-exposure produced a profound increase of total Cd in the blood plasma (approximately 28-fold) and red blood cells (RBC; approximately 20-fold). The plasma Cd-time profiles consisted of an apparent rising (uptake) phase and a declining (clearance) phase with a maximum value of uptake in 4 h, suggesting that uptake of gastrointestinally infused Cd was very rapid. Acclimation to dietary Cd did not affect plasma Cd clearance (approximately 0.5 ml/min), but enhanced new Cd levels in the plasma (but not in the RBC), and resulted in a longer half-life for plasma Cd. Tissue total and new Cd levels varied in different regions of the gastrointestinal tract, and overall levels in gut tissues were much greater than in non-gut tissues, reflecting the Cd exposure route. Dietary Cd, but not the infused Cd, greatly increased total Cd levels of all gut tissues in the order posterior-intestine (640-fold) > cecae (180-fold) > mid-intestine (94-fold) > stomach (53-fold) in Cd-acclimated fish relative to naïve fish. Among non-gut tissues in the Cd-acclimated fish, the great increases of total Cd levels were observed in the liver (73-fold), kidney (39-fold), carcass (35-fold), and gills (30-fold). The results provide some clear conclusions that may be useful for environmental risk assessment of dietary Cd exposure in fish.
authors.affiliation: Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ont., L8S 4K1, Canada. chowdhury.mohammed@epamail.epa.gov
authors.forename: M J
authors.initials: MJ
authors.lastname: Chowdhury
authors.forename: D G
authors.initials: DG
authors.lastname: McDonald
authors.forename: C M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D000064:Acclimatization / Q000187:drug effects*; D000704:Analysis of Variance; D000818:Animals; D001692:Biological Transport; D002104:Cadmium / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000633:toxicity; D002106:Cadmium Radioisotopes / Q000493:pharmacokinetics; D002404:Catheterization; D004032:Diet; D004912:Erythrocytes / Q000378:metabolism; D041981:Gastrointestinal Tract / Q000378:metabolism*; D005880:Gills / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008954:Models, Biological; D017686:Oncorhynchus mykiss / Q000378:metabolism*
chemical_list: D002106:Cadmium Radioisotopes; D002104:Cadmium