Cadmium binding components in the supernatant fraction of the small intestinal mucosa of rats administered cadmium.

Renal damage due to an accumulation of the metal is an important factor in chronic cadmium poisoning. Absorbed cadmium from the intestine contributes to the accumulation of cadmium in the kidney of normal individuals who are free from other occupational exposures to the metal. Thus, information about intestinal cadmium absorption is important for our understanding of chronic cadmium poisoning. Few studies have investigated the absorption of cadmium. It is necessary to investigate the rate, mechanism, sites of absorption, and dietary factors that influence the absorption of cadmium. The retention rates of orally administered cadmium have been reported1-4). And, intestinal cadmium absorption is known to be influenced by various factors5,6) In previous reports we confirmed that the absorption rates of newly administered 109Cd decreased in mice which were orally administered cadmium for set periods. This phenomenon is a convenient and suitable function in the bodies of mice. Recent investigations have shown that a low molecular weight Cd-binding protein, isolated from the kidney and the liver cytosol7-11) is induced by a cadmium injection. This protein is a metallothionein which characteristically is composed of at least 25% cysteine. A similar protein has been identified in rat intestinal cytosol.12) However, the biological role of this protein is not understood. The data presented here identify the intestinal Cd-binding factor induced by the oral administration of cadmium as a metallothionein. This protein may function in the regulation of intestinal cadmium absorption.