In vitro analysis of intestinal absorption of cadmium and calcium in rainbow trout fed with calcium- and cadmium-supplemented diets

Abstract

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 μg Cd g-1 food; the experimental diets were supplemented with CaCO3 and Cd(NO 3)2·4H2O to levels of 50 mg Ca 2+ g-1 food and 300 μg 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. © 2006 The Authors.