Abstract
Recent progress in calcium metabolism has revealed the therapeutic usefulness of active vitamin D3 analogues for senile osteoporosis. However, it has not been well understood the mechanism of accelerated bone mineralization by active vitamin D3 in human senile osteoporosis.
In this report, we examined the effects of 1α-hydroxycholecalciferol (1α-OH D3) on calcium and phosphate metabolism in the elderly subjects. The treatment of 2μg/day of 1α-OH D3 for a week in 6 subjects significantly increased the intestinal calcium absorption rate, serum levels of phosphate and renal reabsorption of phosphate (% TRP). The administration of 0.5μg/day of 1α-OH D3 for 2 weeks in 6 subjects did not change these parameters. Furthermore, no significant changes in the intestinal phosphate absorption, serum level of calcium, iPTH, vitamin D metabolites, blood urea nitrogen, creatinine and Al-Pase activity were observed by the treatment of both doses of 1α-OH D3. The increase in serum phosphate levels after the treatment of 2μg/day of 1α-OH D3 might be due to the increased renal phosphate reabsorption.
These data suggest that increased intestinal calcium absorption and accelerated renal reabsorption of phosphate explain the mechanism of accelerated bone mineralization of active vitamin D3 analogues.
