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Calcium and Vitamin D in Bone Metabolism: Analyses of Their Effects with a Short-Term In Vivo Bone Model in Rats^1,2,

Nutritional Sciences Program and Department of Poultry Science, University of Maryland, College Park, MD 20742 ^* Beltsville Human Nutrition Research Center, U.S. Department of Agriculture, Beltsville, MD 20705

A short-term in vivo system was developed to examine simultaneously bone formation and resorption, and the effects of dietary calcium and vitamin D on these processes. In experiment 1, 25 male Long-Evans rats were each implanted with two gelatin capsules containing mineralized bone (MB) powder subcutaneously in the thorax region. At 4, 6, 8, 10 and 12 d after implantation the acid phosphatase activity (resorption) increased significantly (P < 0.01), whereas alkaline phosphatase activity (formation) did not change. In experiment 2, both MB and demineralized bone (DB) powder were implanted on contralateral dorsal sites of the thorax in 40 male Long-Evans rats and harvested after 7, 9, 11 and 13 d. Enzyme, mineral and histological assessment indicated bone formation in DB implants with bone resorption in MB implants. In experiment 3, the effects of dietary calcium (0.2 or 1.0%) and vitamin D (cholecalciferol at 300 ng/d or 1,25-dihydroxy-cholecalciferol [1,25(OH)₂D₃] at 75 ng/d) were examined using 40 male Long-Evans rats. These rats were implanted with both DB and MB powders and the implants were harvested on d 12. Both low (0.2%) dietary calcium and 1,25(OH)₂D₃ stimulated resorption of MB implants. Therefore, the physiological processes of bone formation and resorption were mimicked in this system of bone powder implants. Further, dietary calcium and 1,25(OH)₂D₃ were shown to modulate these processes.

KEY WORDS: • demineralized bone implants • mineralized bone implants • bone metabolism • calcium • vitamin D

¹ Supported by U.S. Department of Agriculture Grant No. 83-CRCR-1-1238. Scientific Article No. A-4490 Contribution No. 7483 of the Maryland Agricultural Experimental Station.

² Presented in part at the 70th Annual Meeting of the Federation of American Societies for Experimental Biology, April 13–18, 1986, St. Louis, MO [Sinha, R., Smith, J. C. & Soares, J. H. (1986) An experimental short-term model for the study of bone formation and resorption in vivo. Fed. Proc. 45: 327 (abs.)].

³ Present address: Bldg. 37, Rm. 3A19, National Institutes of Health/National Cancer Institute, Bethesda, MD 20892.

⁴ To whom requests for reprints should be addressed.

Manuscript received 8 July 1987. Revision accepted 24 September 1987.

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