MOLYBDENUM-INDUCED CHANGES IN THE EPIPHYSEAL GROWTH-PLATE

Molybdenum (Mo), at high concentrations, induces changes in the epiphy seal growth plate through its effects on copper (Cu) metabolism but it is unclear whether or not Mo can induce changes independent of its ef fects on copper status. To this end, the effect of Mo on longitudinal bone growth was examined in rats. Dietary Mo was given either as ammon ium heptamolybdate or as ammonium tetrathiomolybdate, the latter produ cing a marked Cu deficiency. There was a significant reduction in long itudinal bone growth in both groups; however, growth plate width was i ncreased only in the Cu-deficient animals due to an increase in the wi dth of the zone of transitional/hypertrophic chondrocytes. Both glucos e 6-phosphate dehydrogenase activity and cell proliferation (assessed by bromodeoxyuridine incorporation) were markedly decreased in the pro liferating zone of the growth plate in both Mo-treated groups. These c hanges were not apparently related to changes in circulating vitamin D metabolites or insulin-like growth factor-1. The results indicate tha t excess Mo impairs cell proliferation within the growth plate, wherea s the effects of copper deficiency are more related to chondrocyte dif ferentiation. Thus, Mo can induce changes in longitudinal bone growth which are distinct from those resulting from Cu deficiency.