The Therapeutic Role of 24,25 Dihydroxycholecalciferol in Dialysis Patients with Secondary Hyperparathyroidism. In: Hatano M, editor. Nephrology. Berlin: Springer Berlin Heidelberg; 1991. pp. 455-62. [DOI: 10.1007/978-3-662-35158-1_41]

Effects of 24R,25-dihydroxyvitamin D3 on alkaline phosphatase activity in pig renal epithelial LLC-PK1 cells in culture

1. The effects of 24R,25-dihydroxyvitamin D3 [24,25(OH)2D3] on alkaline phosphatase activity (ALP) were evaluated in pig kidney LLC-PK1 cells in culture. 2. The vitamin D3 metabolite increased ALP activity in these cells, whereas no effect of the hormone was observed on gamma-glutamyltranspeptidase and acid phosphatase activities. 3. ALP activity was stimulated after 3- to 12-hr incubation in the presence of 10(-9) mol/l 24,25(OH)2D3 with a maximum after 6 hr. 4. The hormonal induction of ALP activity was prevented by pretreatment of cells by actinomycin D. 5. It is proposed that 24,25(OH)2D3 could increase ALP activity by de novo protein synthesis.

Bone turnover in rats treated with 1,25-dihydroxyvitamin D3, 25-hydroxyvitamin D3 or 24,25-dihydroxyvitamin D3

Female rats were given 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), 0.25 microgram per 100 g body weight (bw), 25-hydroxyvitamin D3 (25(OH)D3), 1.7 micrograms/100 g bw or 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) 1.7 micrograms/100 g bw, subcutaneously three times a week for 12 weeks. Traditional variables pertaining to calcium homeostasis and growth, i.e. blood and urine calcium (Ca) and phosphate (P), serum levels of vitamin D3 metabolites parathyroid hormone, (PTH), calcitonin (CT), prolactin (PRL) and growth hormone (GH) were measured every four weeks. This data pool was correlated with bone matrix turnover parameters, i.e. serum levels of alkaline phosphatase (ALP) and urinary hydroxyproline (u-HYP) excretion. After 12 weeks of treatment, 1,25(OH)2D3 significantly enhanced serum total and ionized Ca, urine Ca and urine P, and also diminished urine cAMP due to reduced renal function (creatinine clearance). However, 25(OH)D3 administration had no such impact. 24,25(OH)2D3 opposed the effect of 1,25(OH)2D3 after 12 weeks by significantly augmenting serum P and diminishing serum levels of total Ca and ionized Ca. Cross sectional group analyses showed that circulating levels of ALP were directly related with serum 1,25(OH)2D3 and inversely related to serum 24,25(OH)2D3 and CT. Total u-HYP and per cent non-dialysable HYP (ndHYP) were reciprocally and positively correlated with serum PRL, respectively. However, no such relations were observed with serum GH. It appears that rats with elevated circulating levels of 1,25(OH)2D3 exhibit increased bone resorption, while augmented 24,25(OH)2D3 is associated with the opposite. Apparently, high bone turnover (i.e. reduced total urinary HYP and enhanced ndHYP) is associated with high serum PRL.