Long bone calcification in chick embryos acutely- or chronically-treated with aluminum (Al) citrate was investigated. Acutely treated embryos received 100 μl of 60 mM Al citrate, 60 mM sodium (Na) citrate, or 0.7% sodium chloride on day 8 of incubation. Chronically treated embryos received a daily 25 μl dose of the above solutions beginning on day 8. Following 28 days of additional incubation, blood was collected, embryos killed, hind limbs radiographed, and tibias collected. Radiography indicated that Al administration resulted in a persistent angulation in the mid-diaphysis of tibias and femurs and a transient mineralization defect during the 10- to 12- day period of incubation. Tibias from 10- to 12-day embryos which were administered Al contained significantly less (P < 0.005) bone calcium (Ca) compared with tibias from NaCl-treated embryos. By day 14 there were no significant differences among the Ca content of tibias from embryos acutely treated with Al citrate, Na citrate or NaCl. Similarly, the rate of 45Ca uptake by tibias of embryos treated with Al was significantly lower on days 10 (acute) and 12 (chronic) with no significant differences in Ca uptake rate among the three treatment groups by day 16. In each treatment group bone alkaline phosphatase (ALPase) activity increased approximately tenfold between days 10 and 16. At all stages, bone ALPase activity was consistently higher and significantly different (chronic) compared with levels in NaCl- treated embryos. In contrast, Al had no significant effect on the rate of tibia collagen and noncollagenous protein synthesis or serum levels of procollagen carboxy-terminal propeptide (PICP), osteocalcin, and parathyroid hormone (PTH).
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Acknowledgments This work was supported by grants to C.E. Firling from the National Institutes of Health, Institute of Environmental Health Sciences (NIH 1R15 ES05360-01) and the Graduate School of the University of Minnesota. The authors are grateful to M. D. Marko, K. M. Sufka, B. A. Nelson, and N. Swanstrom for their excellent technical assistance. All experiments followed procedures approved by the University of Minnesota Animal Care Committee.
- Alkaline phosphatase
- Aluminum toxicity
- Bone calcification
- Embryonic bone