Molybdenum requirement of rats

Seventy male and seventy female weanling Sprague- Dawley rats were used in two experiments to study the molybdenum (Mo) requirement of rats. In each experiment, the rats were randomly divided into 7 groups of 10 animals each. The liver samples of one group (group 7) were collected at the beginning of the experiments to determine the initial molybdenum concentrations. Group 1 was fed ad libitum AIN-76A diet (basal diet) containing 0.025 mg/kg of Mo. Groups 2-6 were fed the same basal diet supplemented with sodium molybdate to provide total Mo 0.050, 0.100, 0.200, 0.400, 0.800 mg/kg, respectively. The diets were fed for 8 weeks. Effects of dietary Mo on tissue molybdenum, copper, iron, and zinc concentrations and activities ôf Mo-containing enzymes were measured.

In both experiments, Mo concentration in liver increased linearly as dietary Mo increased from 0.025 to 0.200 mg/kg. Beyond this level, no further increase occurred. Brain Mo concentrations increased in the same pattern to plateau at 0.200 mg/kg dietary Mo for the female rats and at 0.100 mg/kg for the male rats. After Mo supplementation, Mo concentrations in heart, spleen and kidney increased significantly to plateau at 0.100, 0.050, 0.050 mg/kg dietary Mo for the female rats and at 0.050, 0.100, 0.100 mg/kg Mo for the male rats, respectively. Copper concentrations in the brain of both male and female rats receiving 0.200 mg/kg Mo were significantly higher than those of the rats in the basal groups (P < 0.05). Mo supplementation significantly increased iron concentrations in the liver, heart and spleen of the male rats (P < 0.05) with peak response at 0.050 mg/kg dietary Mo. Blood iron concentration of the male rats fed 0.200 mg/kg Mo was significantly higher than those of rats fed 0.025, 0.050 and 0.400 mg/kg Mo.

Activities of xanthine dehydrogenase/oxidase (XDH), sulfite oxidase, superoxide dismutase (SOD) in the liver and XDH in the small intestinal mucosa increased significantly (P < 0.05) with increased dietary Mo to plateau at 0.050, 0.050, 0.200, 0.100 mg/kg Mo for the female rats and at 0.050, 0.100, 0.100, and 0.050 mg/kg for the male rats, respectively.

The results of these experiments showed that tissue Mo concentrations and the activities of Mo-containing enzymes reflected the nutritional status of Mo in rats. This study indicated that the Mo requirement of rats fed AIN-76A diet was 0.200 mg/kg.