Effects of Zn status, bile and other endogenous factors on jejunal Cd absorption

The possible contribution of endogenous factors to the control of intestinal Cd uptake was studied in rat jejunum isolated and perfused in situ. If Cd is transported by the same mechanism as Zn, factors influencing Zn absorption should exert similar effects on that of Cd. In spite of an earlier demonstration of interaction between the 2 metals at the level of their intestinal absorption, the increased Zn uptake expected on the basis of previous observations on Zn-deficient rats is not accompanied by increased Cd uptake. The mechanisms involved in Cd and Zn transport in the jejunum are therefore not identical. Cadmium, like Zn and Cu, is readily taken up from a perfusate free of exogenous ligands, so that there is no need to assume an obligatory role of such ligands in Cd absorption. Jejunal Cd transport was strongly depressed by secretions from the bile duct. This inhibition could not be accounted for by the protein content of he bile. On the other hand, micelle-forming bile salts completely abolished Cd absorption at or above a level corresponding to their critical micellar concentration. It is suggested that bile salts represent one endogenous factor which might be involved in preventing extensive Cd uptake from the intestinal lumen.