Metabolism of109Cd in rats fed normal and low‐calcium diets

Abstract

Growing male rats were fed purified diets that contained either 0.6% or 0.1% calcium to investigate the relationship of calcium intake to the uptake, tissue distribution, and excretion of ¹⁰⁹ Cd. An equal number of rats were fed either the 0.6 or 0.1% calcium diets for 4 wk before they were used for experiments. In the first experiment 11 rats from each dietary group were administered 5 μCi ¹⁰⁹ Cd by stomach tube and were then maintained in metabolism cages for 72 hr. Animals fed the low‐calcium diet took up more ¹⁰⁹ Cd, as significantly higher levels of radioactivity were found in the intestinal mucosa, serum, lungs, liver, kidneys, and urine and a significantly lower level was found in the feces. Higher levels of ¹⁰⁹ Cd, associated with low‐molecular‐weight proteins that may be related to the absorption process, were found in the intestinal mucosa of the low‐calcium group. In the second experiment 10 rats from each dietary group were administered 5 μCi ¹⁰⁹ Cd by subcutaneous injection and then maintained in a metabolism cage for 72 hr. No significant differences were found in the distribution or excretion of ¹⁰⁹ Cd except for the lungs where radioactivity was greater in the low‐calcium group. The results of the study indicate that the enhanced cadmium toxicity observed in calcium‐deficient animals exposed to the heavy metal is the result of an increased uptake from the small intestine.