Studies on Poisonous Metals. VII. Effects of Proteins and Amino Acids on the Small Intestinal Absorption of Cadmium in Rats

Abstract

The effects of various proteins and amino acids on the in situ rat small intestinal absorption of cadmium were studied. Proteins such as glycinin, ovalbumin, and β-lactoglobulin significantly decreased the intestinal absorption of cadmium. On the other hand, amino acids such as L-cysteine, L-histidine, and L-proline promoted the absorption of the metal. We concluded that proteins which are little absorbed from the small intestine decrease the amount of free cadmium available to be transported across the intestinal wall by binding the metal, resulting in depression of the absorption of the metal. On the other hand, the stimulatory effect of amino acids on the intestinal absorption of cadmium occurs because amino acids taken up into the mucosal tissue depress the binding of cadmium to the intestinal tissue by the formation of complexes with the metal, and the relatively stable complex of amino acid with cadmium, which is formed in the lumen, is transported across the intestinal wall.