Effects of dietary zinc depletion and food restriction on intestinal transport of cadmium in the rat.

The effects of Zn depletion and short-term fasting on intestinal transport of Cd were examined in perfused rat small intestines. The small intestine was isolated with its vascular network intact, then simultaneously perfused from the luminal and vascular sides. A Zn-depleted state that results in marked hypozincemia was produced in some rats by feeding a Zn-deficient diet for 4 days. Uptake of Cd from the luminal perfusate was greater in the Zn-depleted rats, whereas transport of Cd to the vascular perfusate was not affected. Fasting overnight prior to perfusion did not influence Cd transport nor alter the effect of Zn depletion on Cd uptake. The Cd concentration in the soluble fraction of intestinal mucosa from perfused intestines was not different between Zn-depleted and Zn-adequate rats. Gel filtration chromatography of the soluble fraction showed a shift in the distribution of Cd from metallothionein to high molecular weight ligands in intestines from Zn-depleted rats. The decrease in amount of metallothionein-associated Cd corresponded to a decrease of total intestinal metallothionein as measured by the Cd-binding assay. The results suggest association of Cd with intestinal metallothionein did not influence the absorption of Cd under these conditions.