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 mu g Cd g(-1) food; the experimental diets were supplemented with CaCO3 and Cd(NO3)(2).4H(2)O to levels of 50 mg Ca2+ g(-1) food and 300 mu g Cd g(-1) food, alone and in combination. The Ca2+ and Cd absorption rates were measured using radiotracers (Ca-45, Cd-109) 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. (c) 2006 The Authors Journal compilation (c) 2006 The Fisheries Society of the British Isles.