Abstract
While 1,25 (OH)2D3 is known to promote bone resorption in vitro little is known about the action of this metabolite on matrix formation and mineralization. This question is particularly important in view of recent controversy on which metabolite of vitamin D promotes mineralization and cures oesteomalacia. Therefore the effect of 1,25 (OH)2D3 on growth cartilage and on endosteal bone was studied in tissue culture.
Material and methods
Calvaria and proximal tibial growth cartilage were prepared from baby rats with rickets (4 weeks). Specimens were incubated in Eagles medium, modified after Dulbecco, for 1-6 days in the presence or absence of 4 × 10−8M 1,25(OH)2D3 and studied by transmission and scanning electron microscopy (critical point drying method). In a recovery experiment calvaria were incubated with 1,25 (OH)2D3 for 1 day and transferred into a medium without the metabolite for a second incubation period of 1-6 days.
Results
In ricketick cartilage we found numerous matrix vesicles in the longitudinal septa, which contained no mineral deposits. After 3 days of incubation, both groups (without and with 1,25) showed mineral material. At day 4 mineral crystals were seen outside the vesicles. At day 6 longitudinal septa of both groups were completely mineralized. In the absence of 1,25 calvaria were covered by flat lining cells. After 1 day exposure to 1,25 osteoid was denuded nearly completely, because all lining cells were transformed into globiform cells. After 2 days incubation with 1,25 proliferating fusiform cells appeared.
No osteoclasts were visible.
In our recovery experiment we found that 1,25 induced changes of lining cell's morphology were reversible within a period of 6 days.
Conclusion
1,25(OH)2D3 has no direct effect on the mineralization process of cartilage in vitro. In contrast to in vivo studies, this model precludes changes in Ca of P balance or plasma concentrations.
1,25(OH)2D3 has a dramatic effect on surface lining cells (morphology, proliferation),which are similar to the effects of parathyroid hormone.
In a further experiment we try to analyse the effect of 24,25 vitamin D on cartilage and endosteal lining cells in our in vitro system.
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Klimpel, F., Krempien, B. Influence of 1,25 (OH)2D3 on osteoblasts and on mineralization of cartilage. In vitro experiments: 30. Pediatr Res 14, 170–171 (1980). https://doi.org/10.1203/00006450-198002000-00057
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DOI: https://doi.org/10.1203/00006450-198002000-00057