Tissue distribution of cadmium in rats given minimum amounts of cadmium-polluted rice or cadmium chloride for 8 months

To investigate the relationship between cadmium (Cd) toxicity, intestinal a bsorption, and its distribution to various tissues in rats treated orally w ith minimum amounts of Cd, 14 female rats per dose group per time point wer e given diets consisting of 28% purified diet and 72% ordinary rice contain ing Cd-polluted rice (0.02, 0.04, 0.12, or 1.01 ppm of Cd) or CdCl2 (5.08, 1.9.8, or 40.0 ppm of Cd) for up to 8 months. At 1, 4, and 8 months after t he commencement of Cd treatment, seven rats per group were euthanized for p athological examinations to determine the Cd concentrations in the liver an d kidneys and metallothionein (MT) in the liver, kidneys, intestinal mucosa , serum, and urine. One week before each period of 1, 4, and 8 months, the remaining seven rats in each group were administered a single dosage of Cd- 109, a tracer, to match the amounts of the designated Cd doses (about 1.2 t o 2400 mu g/kg body wt). They were euthanized 5 days later to determine the distribution of Cd to various tissues. No Cd-related toxic changes were ob served. The concentrations of Cd in the liver and kidneys at any time point and MT in the liver, kidney, serum, and urine at 4 and 8 months increased dose-dependently, whereas MT in the intestinal mucosa did not alter markedl y at any time point. The distribution rates of Cd to the liver increased do se-dependently (40% at lower doses to 60% at higher doses), whereas those t o the kidney decreased dose-dependently (20% at lower doses to 10% at highe r doses). The Cd retention rates 5 days after Cd-109 administration (amount s of Cd in various tissues/amounts of Cd administered) ranged from 0.2 to 1 .0% at any time point. These results suggest that the distribution of Cd to the liver and kidneys after the oral administration vary depending on the dosage levels of Cd. The difference of the distribution pattern of Cd to th e liver and kidney is probably due to the difference in the form of the abs orbed Cd, i.e., free ion or Cd-MT complex, although not closely related to the MT in the intestinal mucosa. (C) 1999 Academic Press.