The influence of molybdenum on the copper metabolism of the rat at different Cu levels of the diet.

1. Male WAG/Cpb inbred rats fed on rations with approximately 1.5 mg copper/kg (deficient), 6.0 mg Cu/kg (adequate) and 25.0 mg Cu/kg (excess) were supplemented with varying amounts of molybdenum (0, 50, 150 and 500 mg/kg diet) and the effect on the Cu concentration of blood, plasma, liver and kidney, the caeruloplasmin activity of plasma and the Mo concentration of liver and kidney were studied. 2. Mo increased the Cu concentration of blood, plasma, liver and kidney and the Mo concentration of liver and kidney. 3. In the plasma of Mo-supplemented rats the presence of a Cu-containing fraction was demonstrated, the Cu of which did not react with dithiocarbamate and was not related to caeruloplasmin. The Cu in this fraction was not able to increase the caeruloplasmin activity in the plasma of Cu-deficient Mo-supplemented rats. The Cu concentration of the erythrocytes did not seem to have been increased by the Mo treatment. 4. When compared to Cu-adequate rats the effect of Mo on the Cu distribution was reduced both by Cu deficiency and Cu excess. This decreased effect of Mo was explained by reduced uptake or retention of Mo in the body as observed in the liver and kidney.