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The Effect of Dietary Calcium on Bone Metabolism in Young and Aged Female Rats Using a Short-Term In Vivo Model^1,2,

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

The use of high dietary calcium supplementation in the treatment of patients with osteoporosis is controversial. The present study examined the mechanisms underlying the effects of calcium supplementation by investigating the influence of dietary calcium on bone dynamics in young and aged rats. A 2 x 2 x 2 factorial design was utilized with 0.2% (low) or 1.0% (high) calcium, 2- or 24-m-old female Long-Evans rats that were implanted subcutaneously with demineralized (DB) and mineralized (MB) bone powder. The four groups of rats were fed each of the respective diets for 11 wk and then implanted with one #5 gelatin capsule containing 30 mg of DB and another containing 100 mg of MB powder. The animals were injected intraperitoneally with 0.1 µCi/g body weight with ⁴⁵Ca 14 h before the end of experiment. The ectopic bone as well as the right femurs were harvested 14 d after the rats were implanted. Marker enzyme activities (alkaline-formation and acid-resorption phosphatase), ⁴⁵Ca uptake and calcium content were measured in the implants and the distal epiphyses of the right femurs. Bone turnover was higher in the young rats than in the old animals, and high dietary calcium in the young animals increased bone formation, as indicated by alkaline phosphatase activity. Dietary calcium level did not affect ectopic bone formation or resorption in the aged rats. The results indicate that high dietary intake of calcium does not affect bone dynamics in aged female rats but does increase bone formation in young rats.

KEY WORDS: • dietary calcium • aging • bone metabolism • demineralized and mineralized bone implants

¹ Supported by part by USDA Grant No. 83-CRCR-1-1238 and in part by an award to R. Sinha from The Aging Institute, University of Maryland.

² Presented in part at the Seventy-First Annual Meeting of the Federation of American Societies for Experimental Biology, March 29–April 2, 1987, Washington, DC. [Sinha, R., Smith, J. C. and Soares, J. H. (1987) Effect of dietary calcium on net bone loss in aged rats. Fed. Proc. 46: 3397 (abs.)].

³ Present address: National Institutes of Health/National Cancer Institute, Bldg. 387, Rm. 3A19, Bethesda, MD 20892.

⁴ To whom requests for reprints should be addressed.

Manuscript received 11 December 1987. Revision accepted 24 May 1988.