Inhibitory effects of active vitamin D preparations on PTH secretion in rats

Prevention and treatment of glucocorticoid-induced osteoporosis with active vitamin D3 analogues: a review with meta-analysis of randomized controlled trials including organ transplantation studies

The aim of this review with meta-analysis was to determine if there is a rationale to use activated forms of vitamin D3 to treat or prevent glucocorticoid-induced osteoporosis, and to compare the effect of active vitamin D3 metabolites with that of other anti-osteoporosis therapies. We performed a systemic search using MEDLINE/PubMed (1966-2003). Animal studies and clinical trials involving humans with data on therapy to treat or prevent glucocorticoid-induced osteoporosis with active vitamin D3 analogues were included. Animal studies and basic research studies with active vitamin D3 were reviewed (qualitative review). Meta-analysis (quantitative review) on clinical trials (including organ transplantation studies) was performed with percent change in lumbar spine bone mineral density or bone mineral content as the primary outcome measure; the secondary outcome measure was incidence of vertebral fractures. Fifty-four articles were found. Animal and basic research studies showed that active vitamin D3 analogues can inhibit bone loss during treatment with glucocorticoids. Concerning the effect on bone mineral density, the pooled effect size of active vitamin D3 analogues compared with no treatment, placebo, plain vitamin D3 and/or calcium was 0.35 (95% confidence interval (CI) 0.18, 0.52). Compared with bisphosphonates, the pooled effect size was -1.03 (95% CI -1.71, -0.36). The pooled estimate of the relative risk for vertebral fractures of active vitamin D3 analogues compared with no treatment, placebo, plain vitamin D3 and/or calcium was 0.56 (95% CI 0.34, 0.92) and compared with bisphosphonates it was 1.20 (95% CI 0.32, 4.55). Active vitamin D3 analogues not only preserve bone during glucocorticoid therapy more effectively than no treatment, placebo, plain vitamin D3 and/or calcium, but are also more effective in decreasing the risk of vertebral fractures. Bisphosphonates, however, are more effective in preserving bone and decreasing the risk of vertebral fractures than active vitamin D3 analogues.

Reduced binding of [3H]1,25-dihydroxyvitamin D3 in the parathyroid glands of patients with renal failure

This study examined the hypothesis that altered binding of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) to parathyroid receptors might be involved in the pathogenesis of secondary hyperparathyroidism associated with chronic renal failure. The binding of [3H]1,25-(OH)2D3 to hyperplastic parathyroid glands obtained from seven patients with chronic renal failure was measured. These values were compared with those for binding to hyperplastic parathyroid tissue obtained from six patients who had received renal transplants and for binding to parathyroid adenomas removed from five patients who had primary hyperparathyroidism. We found that Nmax (an estimate of the concentration of 1,25-(OH)2D3 receptors) was reduced (42 +/- 15 fmol per milligram of protein) in patients with chronic renal failure as compared with patients with transplanted kidneys (78 +/- 24 fmol per milligram of protein) and patients with primary hyperparathyroidism (114 +/- 30). Nmax correlated inversely with the severity of renal dysfunction, the serum level of phosphorus, and the logarithm of the serum level of immunoreactive parathyroid hormone. These observations suggest that 1,25-(OH)2D3 binding by parathyroid tissue is reduced in chronic renal failure. This may contribute to the pathogenesis of secondary hyperparathyroidism by reducing the inhibition by 1,25-(OH)2D of parathyroid hormone secretion. The low serum levels of 1,25-(OH)2D in chronic renal failure may accentuate this effect.