Controlled trial shows intact vitamin D synthesis following parathyroid hormone challenge in elderly osteopenic adults, suggesting bone loss stems from upstream regulatory defects.
This study was carried out to evaluate the effects of an iv injection of parathyroid extract on serum levels of 1,25-dihydroxyvitamin D [1,25-(OH)2D3] in elderly osteopenic patients and age-matched nonosteopenic controls. Serum concentrations of 1,25-(OH)2D were reduced in elderly osteopenic subjects (mean +/- SEM, 20 +/- 3 pg/ml) compared with values in age-matched nonosteopenic controls (35 +/- 3 pg/ml), whereas no differences were found in serum 24,25-dihydroxyvitamin D levels (1.5 +/- 0.3 and 2.2 +/- 0.5 ng/ml, respectively). An iv injection of parathyroid extract was followed by a significant increase in serum 1,25-(OH)2D levels in both osteopenic patients (16 +/- 6 pg/ml) and controls (15 +/- 5 pg/ml). The mean 4-h increases in serum 1,25-(OH)2D of 11-18 pg/ml were not significantly different in the two groups. The results indicate that the reduced 1,25-(OH)2D concentrations in the osteopenic patients are secondary to changes in factors that normally stimulate this enzyme system.
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Sørensen et al. (1982) studied this question.
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