The effect of oral phosphate administration on major indices of skeletal metabolism in normal subjects

The effect of brief periods of phosphate administration on indices of human skeletal metabolism was investigated. Thirteen subjects (8 women, 5 men; 19–36 years old) received 2 g of oral phosphate daily for 5 days. Serum phosphorus rose 26% (3.8 ± 0.1 mg/dl to 4.8 ± 0.1 mg/dl; p < .01) while total calcium fell (9.3 ± 0.1 mg/dl to 8.9 ± 0.1 mg/dl; p < .01). Parathyroid hormone levels increased by 50% (14.1 ± 2.0 pg/ml to 21.5 ± 1.7 pg/ml; p < .05) although values remained within the normal range. A persistent phosphaturia (0.64 ± 0.10 g/g Cr to 1.8 ± 0.4 g/g Cr; p < .05) and a 69% fall in urinary calcium (80.8 ± 10.0 mg/g Cr to 24.6 ± 6.0 mg/g Cr; p < .001) were observed. 1,25-dihydroxyvitamin D3 and urinary hydroxyproline concentrations did not change significantly but the bone γ-carboxyglutamic acid protein (BGP) concentration rose 41% by day 2 (9.6 ± 1.3 mg/ml to 13.5 ± 2.2 mg/ml; p < .005) and remained elevated throughout the study period. These results support the possibility that brief periods of phosphate administration may be useful in the therapy of disorders associated with low bone turnover, such as osteoporosis.