Assessment of Vitamin D Metabolites and Combination of 1α, 25-Dihydroxyvitamin D3 and Parathyroid Hormone on Mineralization of Embryonic Chick Femurs in Organ Culture

Abstract

Organ culture system was used to evaluate the effects of vitamin D metabolites,1α,25-dihydroxyvitamin D₃(1,25(OH)₂D₃),1α-hydroxyvitamin D₃(1αOHD₃)and 24R,25-dihydroxyvitamin D₃(24,25(OH)₂D₃).and the combination of 1,25(OH)₂D₃ and bovine parathyroid hormone (1-34)on mineralization of the 10-day embryonic chick femurs in vitro. The embryonic chick femurs were cultured in the control medium during 5 days, and were kept in the several experimental mediums containing vitamin D metabolites at concentration of 10^-11-10^-8 M or both 10^-8 M 1,25(OH)₂2D₃ and 0.1nM PTH during an additional 5 days. The contents of calcium (Ca), phosphorus (P) and magnesium (Mg) in bones cultured in the control medium increased in the order of the 10-day cultures,5-day cultures and 10-day embryonic chick femurs as culture period goes on. The activities of both alkaline phosphatase (ALP) and acid phosphatase (ACP)were higher in the 10-day cultures with the control medium than those in the 10-day embryonic chick femurs. The Ca content in the cultured bones decreased in the treatment with 1,25(OH)₂D₃ at concentration of 10^-10-10^-8 M, and increased in the treatment with 1αOHD₃ at concentration of10^-10-10^-8 M, and was no change in the treatment with 24,25(OH)₂D₃. There was no change in the P content in the cultured bones treated with 1aOHD3 and 1,25(OH)D₂D₃. Its content of bones cultured with 10^-8 M 1,25(OH)₂D₃ decreased. The activities both ALP and ACP did not change in the cultured bones with vitamin D metabolites. The contents of Ca and P in the cultured bones increased in the bPTH (1-34) (PTH) treatment. The calcium content in the cultured bones with the combination of 1,25(OH)₂D₃ and PTH was higher than that of the PTH alone. The ALP activity in the cultured bones decreased in the PTH treatment to the half level of the 5-day cultures with the control medium, and increased in the combination of 1,25(OH)₂D₃ and PTH treatment compared with the PTHtreatment. The contents of total protein, collagen and noncollagenous protein in the cultured bones decreased in the 10^-8M 1,25(OH)²D³ treatment. These results indicated that 1,25(OH)²D³ stimulated bone resorption, and 1αOHD³ increased bone formation, and that 1,25(OH)²D³ augmented the bone formation induced by PTH alone. This organ culture system may provide a good means for estimation of efficacy of various substances influencing bone-remodeling.