In vitro analysis of intestinal absorption of cadmium and calcium in rainbow trout fed with calcium- and cadmium-supplemented diets
The protective effects of dietary Ca2+ supplementation against Cd accumulation in rainbow trout Oncorhynchus mykiss fed with Cd-contaminated food were evaluated in relation to chronic changes in intestinal absorption rates. The changes were measured ‘in vitro’. The control diet contained c. 20 mg Ca2+ g−1 food and 0·25 g Cd g−1 food; the experimental diets were supplemented with CaCO3 and Cd(NO3)2·4H2O to levels of 50 mg Ca2+ g−1 food and 300 g Cd g−1 food, alone and in combination. The Ca2+ and Cd absorption rates were measured using radiotracers (45Ca, 109Cd) at total Ca2+ and Cd concentrations of 3·0 and 0·12 mmol l−1, respectively in the intestinal saline. Chronically elevated dietary Cd caused a significant increase in Cd absorption rate by up to 10-fold at 30 days in the mid-intestine. The high Ca2+ diet prevented this up-regulation of Cd transport rate. Conversely, intestinal Ca2+ absorption was significantly increased by two- to five-fold by the Ca2+-supplemented diet at 30 days in both the mid- and posterior intestine, and this effect was eliminated when Cd was simultaneously elevated in the diet. Ca2+ and Cd probably interact at common pathways and transport mechanisms in the intestine, though independent pathways may also exist.
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