Bone loss was previously shown to be induced in the femoral tissue of regucalcin transgenic (TG) rats. Regucalcin is expressed in rat bone marrow cells and its expression is enhanced in regucalcin TG rats. This study was undertaken to determine the change in osteoclastic bone resorption in regucalcin TG rats with increasing age. Femoral-diaphyseal and -metaphyseal tissues were obtained from normal (wild-type) and regucalcin TG rats aged 5, 14, 25 or 50 weeks. Calcium content in the femoral-diaphyseal and -metaphyseal tissues was significantly decreased in regucalcin TG male and female rats aged 5, 14, 25 or 50 weeks as compared with the value obtained from normal rats with each age. When the marrow cells obtained from normal or regucalcin TG rats were cultured for 7 days, the number of tartrate-resistant acid phosphatase (TRACP), a marker of osteoclasts, positive multinucleated cells (MNCs) were significantly increased in the marrow culture of regucalcin TG male and female rats aged 5, 14, 25 or 50 weeks. The effect of parathyroid hormone [human PTH (1-34); 10−7 M] or 1,25-dihydroxyvitamin D3 [1,25(OH)2D3; 10−7 M] in stimulating TRACP-positive MNC formation was significantly enhanced in regucalcin TG male and female rats aged 14 or 25 weeks. This study demonstrates that osteoclastic bone resorption is stimulated in regucalcin TG male and female rats with increasing age.

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