Differential effects of calcium-regulating hormones on bone metabolism in weanling rats orally administered zinc sulfate

The effect of calcium-regulating hormones on bone metabolism was investigated in weanling rats orally administered zinc sulfate. Administration of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3 (150 ng/100 g BW) or parathyroid hormone (1-34) (PTH) (10 U/100 g) produced significant increases in alkaline phosphatase activity and DNA content in the femoral diaphysis, while calcitonin (CT) (1.0 U/100 g) did not have a significant effect. Administration of zinc (1.0 mg/100 g) caused a significant elevation of alkaline phosphatase activity and DNA content in the femoral diaphysis. In combination with these hormones and zinc, both 1,25(OH)2D3 and zinc caused a synergistic increase in diaphyseal alkaline phosphatase activity and DNA content, while the combination with zinc and PTH, or zinc and CT did not cause a synergistic increase. The synergistic effects in combination with 1,25(OH)2D3 and zinc were completely inhibited by treatment of mitomycin C (10 micrograms/100 g). Meanwhile, the increase in diaphyseal zinc content following zinc administration was not altered by treatment with 1,25(OH)2D3. These results indicate that zinc synergistically enhances 1,25(OH)2D3-stimulated bone metabolism. This suggests a physiologic significance of zinc in the regulation of bone metabolism.