Influence of a low calcium and phosphorus diet on the anabolic effect of human parathyroid hormone (1-38) in female rats

Parathyroid hormone (PTH) or synthetic N-terminal PTH fragments administere d intermittently have been established as anabolic agents in animal and hum an bones. In the present study, the influence of a low calcium diet on the anabolic effect of human PTH(1-38) [hPTH(1-38)] was investigated. Forty-eig ht 10-week-old female Sprague-Dawley rats were randomly assigned to a diet with a low calcium content (LCa) or a diet with the recommended amount of c alcium (RCa). After an adaptation period of 15 days, the rats were randomly assigned to hPTH(1-38) treatment (+LCa/+RCa) or vehicle only (-LCa/-RCa) f or an additional 14 days. Total bone mineral density (BMD) values of severa l bones were determined using quantitative computed tomography and from rat ios of ash weight to volume. Biomechanical competence of the fourth lumbar vertebrae and of the right femora was assessed. An anabolic effect could be detected in both PTH-treated groups. However, the bones of the +LCa group showed significantly lower BMD and also a diminished increase in maximal br eaking force compared with those of the +RCa group. The study demonstrates that the anabolic effect of hPTH(1-38) is blunted by the LCa diet. This sug gests that, during PTH treatment, dietary calcium intake is critical. (C) 2 001 by Elsevier Science Inc. All rights reserved.