Effects of Molybdate and Tetrathiomolybdate Supplementation of Drinking Water on Immature Rats Infected with Nippostrongylus brasiliensis. 2. Copper Status and Tissue Molybdenum Accretion

Molybdate (MoO4) and tetrathiomolybdate (MoS4) supplementation of rats via drinking water had opposite effects on the establishment of Nippostrongylus brasiliensis larvae but both induced hypercupraemia, temporarily inhibited activities of superoxide dismutase in liver and duodenum after infection and enlarged the femoral head. Effects of MoO4 and MoS4 on activities of caeruloplasmin oxidase (CpO) in plasma, erythrocyte superoxide dismutase (ESOD) and tissue copper (Cu) and molybdenum (Mo) were compared to test the hypothesis that species lacking a rumen can thiolate MoO4. Three groups of 18 immature Wistar rats were given Mo (70 mg/L as MoO4) or MoS4 (5 mg/L) via drinking water or remained untreated; all received a commercial, cubed diet and 12 from each group were infected with larvae of N. brasiliensis. Rats were killed 7–9 days later and liver, kidney, spleen, heart, muscle (quadriceps), brain and bone (femur) removed for Cu and Mo analysis. Plasma Cu was greatly increased by MoO4 and MoS4, without changing CpO activity, but the effect was more variable with MoO4 and accompanied by a smaller decrease in ESOD. Tissue Cu and Mo were increased by MoS4 in all tissues examined except brain and bone, correlating with plasma Cu and with each other; relationships were strongest in spleen, followed by kidney. MoO4 also increased soft tissue Cu and Mo but increases were generally smaller than those induced by MoS4 and correlations between the two elements and with plasma Cu generally weaker. Since hypercupraemia and correlated increases in liver and kidney Cu and Mo are characteristic of systemic thiomolybdate (TM) exposure, we conclude that MoO4 was partially thiolated to give a different TM profile from that produced by MoS4. The pathophysiological significance of systemic exposure to di- and tri-TM merits investigation in non-ruminants as agents of chelation therapy and in ruminants as agents of short-lived TM toxicity on Mo-rich pastures.