THE LONGITUDINAL DISTRIBUTION OF CADMIUM, ZINC, COPPER, IRON, AND METALLOTHIONEIN IN THE SMALL-INTESTINAL MUCOSA OF RATS AFTER ADMINISTRATION OF CADMIUM CHLORIDE

Different routes of Cd intake may influence the intestinal distributio n of Cd, metallothionein (MT), and trace metals differently. Therefore , we compared the effects of parenteral and enteral administration of Cd on the distribution of trace metals and MT along the small intestin e. In a first experiment three groups of rats were employed: a control , one receiving CdCl2 within the drinking water, and another receiving sc injections of CdCl2. In a second experiment, rats were fed three d ifferent diets with either 0, 0.3, or 1 mmol CdCl2/kg for one and two weeks to study the time- and dose-dependent effects of orally administ ered Cd. Metal concentrations (Cd, Zn, Cu, Fe) were measured by atomic emission spectrometry and MT was determined by radioimmunoassay. Inte stinal MT levels did not show proximodistal gradients in controls or a fter sc administration of Cd, but orally administered Cd increased muc osal MT levels longitudinally from the duodenum to the ileum. Cd level s paralleled those of MT. Compared with the metal concentrations in th e controls, sc administration of Cd did not change intestinal Zn, Cu, and Fe levels. Oral administration of Cd, however, increased Cu and de creased Fe levels in the intestinal mucosa significantly. The second e xperiment revealed that only high dietary concentrations of Cd increas e intestinal Cd and MT levels longitudinally toward the distal parts, whereas at lower dietary concentration the longitudinal distribution w as reversed. This shows that different routes and doses of Cd intake l ead to a different trace metal and MT distribution and emphasizes the role of dietary Cd in the local induction of small-intestinal MT.-