Absorption interactions of zinc and cadmium in the isolated perfused rat intestine

Interactions between zinc and cadmium using either 65Zn or 109Cd in separate experiments were studied using an isolated rat intestinal preparation. In all experiments, the intraluminal concentrations of Zn were 0, 5, 10 or 20 mg/L and 0, 0.03, 0.10, 1.00 and 10.0 mg/L for Cd. In the first series using 109Cd, the amount of Cd found in the vascular effluent (VE) was significantly increased by the presence of Zn in comparison with control perfusions (no Zn present in the luminal perfusate). Zn had no significant effect on the amount of Cd retained by the gut tissue except at the lowest Cd concentration (0.03 mg/L), at which Zn concentrations of 10 and 20 mg/L significantly reduced the amount of Cd retained by the tissue. In the second series using 65Zn, Cd reduced the amount of Zn appearing in the VE. This effect was particularly marked when the Zn concentration was low. Cd had no effect on Zn retained by the tissue except at the highest concentration, when it increased the tissue Zn content. Binding of the metals to the intracellular protein metallothionein (MT), as well as to higher molecular weight proteins (HMWP), in both series of experiments was studied by gel fractionation of the 100,000 g supernatants of epithelial cell homogenates. When no Zn was present, the amount of labelled Cd-MT increased as the Cd intraluminal dose was increased. The further addition of Zn into the lumen during the perfusion period resulted post-perfusion in a decrease in labelled Cd-MT.(ABSTRACT TRUNCATED AT 250 WORDS)