Copper and molybdenum absorption by rats given ammonium tetrathiomolybdate

Previous studies have shown that the tetrathiomolybdate ion [MoS_4^2?] is a potent antagonist of Cu metabolism. Effects of orally administered MoS_4^2? on the absorption and tissue distribution of ⁶⁴Cu in rats have now been investigated. Four or 12 mg Mo/kg diet, when given as MoS_4^2?, strongly inhibited ⁶⁴Cu absorption and modified the fate of absorbed Cu, decreasing hepatic and renal uptake but increasing plasma retention of ⁶⁴Cu. These effects were not induced by equivalent dietary concentrations of Mo as MoS_4^2? or when S^2? was given as CaS. Clinical and biochemical effects induced by orally administered MoS_4^2? were abolished by increasing dietary concentrations of Cu. Such treatment also inhibited the absorption and tissue retention of ⁹⁹Mo derived from ⁹⁹MoS_4^2?. Intraperitoneal administration of Cu ameliorated clinical effects attributable to MoS_4^2? but neither inhibited ⁹⁹Mo absorption nor the appearance of systemic defects in Cu metabolism. Since the absorption of MoS_4^2? (or its derivatives) from the gastrointestinal tract is inhibited by Cu, it is evident that the site of its action as an antagonist influencing either the absorption or the subsequent metabolic fate of Cu depends upon the ratio Cu/MoS_4^2? in the diet.     

Intestinal metallothionein and the mutual antagonism between copper and zinc in the rat.

A study has been made of the mechanism of the mutual antagonism between copper and zinc in rats. Dietary zinc concentrations of up to 450 mg/kg had no effect on intestinal 64Cu absorption but 900 mg/kg caused a 40% reduction. This was associated with an increase in the mucosal uptake of 64Cu in the small intestine. This occurred mainly in the form of metallothionein and it appeared that copper displaced zinc from the protein after its synthesis had been induced by zinc. Ths intestinal absorption of 65Zn was decreased by 20% when the dietary copper intake was increased from 3 to 24 mg/kg. Further increases in copper intake to 300 mg/kg did not cause any additional decrease in 65Zn absorption or any change in the association of intestinal 65Zn with metallothionein. Concentrations of this protein in the intestinal mucosa were not influenced by dietary copper intake.     

Effect of acute stress on the absorption and distribution of zinc and on Zn-metallothionein production in the liver of the chick.

A study has been made of the effects of chloroform inhalation, Escherichia coli endotoxin injection and hydrocortisone injection on the absorption of a single intragastric dose of 65Zn by the chick. Injection of hydrocortisone increased the absorption of the 65Zn by 30-55% in both Zn-deficient and Zn-supplemented chicks. The influence of chloroform and endotoxin was less consistent; the former treatment only increased 65Zn absorption and endotoxin was less consistent; the former treatment only increased 65Zn absorption in Zn-supplemented chicks fed ad libitum whereas endotoxin only increased that in Zn-supplemented chicks on a restricted food intake. Injection of endotoxin increased the hepatic uptake of the absorbed 65Zn in both Zn-deficient and Zn-supplemented chicks, whereas hydrocortisone had a similar effect in the Zn-supplemented birds only. Chloroform inhalation increased hepatic 65Zn uptake in Zn-deficient chicks only. The increase in hepatic Zn concentrations in the stressed chicks was mainly associated with a protein in the cytosol identified as metallothionein. Both endotoxin and hydrocortisone decreased total plasma Zn concentrations in Zn-supplemented and Zn-deficient chicks; chloroform decreased plasma 65Zn content only.     

The effects of age,sex, and zinc status on the accumulation of (copper,zinc)-metallothionein in rat kidneys

A study has been made of the distribution of copper in the kidneys of growing rats. Renal copper concentrations increased steadily with age and were greater in female than in male animals. Most of the copper was present as (copper, zinc)-metallothionein and two forms of this protein were isolated and characterized from the kidneys of mature female rats. That copper metabolism in kidneys is subject to hormonal influence was indicated by a reduction in the concentrations of copper and (copper, zinc)-metallothionein in ovariectomized rats and by an increase in their concentrations after the administration of progesterone. Concentrations of renal (copper, zinc)-metallothionein were less in zinc-deficient than in zinc-adequate rats during pregnancy and after progesterone administration.