A possible direct effect of 24,25-dihydroxycholecalciferol on the parathyroid gland in patients with chronic renal failure

No short-term effects of 24,25-dihydroxycholecalciferol in healthy subjects

Seven healthy volunteers were given 25 micrograms of 24,25-DHCC for one week to study the effects on calcium and bone metabolism. Mean plasma 24,25-DHCC concentration increased from 2.2 +/- 1.7 micrograms/l to 10.8 +/- 6.1 micrograms/l (p less than 0.001). No significant change was seen in the fasting plasma concentrations of Ca, Ca++, PTH and alkaline phosphatase activity and in urinary excretion of calcium and hydroxyproline and in tubular reabsorption of phosphate. The area under the curve for plasma ionized calcium concentration and urinary excretion of calcium during a standard calcium infusion of 10 mg/kg of Ca in 2 h did not change by 24,25-DHCC. We conclude that in healthy subjects no effect of 24,25-DHCC on the steady state parameters of calcium and bone metabolism, on renal calcium handling and on the handling of an intravenous calcium challenge by the homeostatic system could be demonstrated.

Vitamin D metabolite profiles in moderate renal insufficiency of childhood

In a prior study, we reported vitamin D metabolite profiles in the plasma of healthy children. In view of these findings, we investigated these same profiles in children with moderate renal insufficiency. Specimens were obtained in both summer and winter in untreated patients, and before and after treatment for up to 1 year, with either 25(OH)D3 or 1,25(OH)2D3. Mean pretreatment 1,25(OH)2D levels were normal. Levels of 25(OH)D3 were also normal and continued to vary with season. Mean pretreatment 24,25(OH)2D3 levels were significantly lower in patients and, interestingly, did not show the normal seasonal variation. Treatment with 25(OH)D3 resulted in consistent and sustained rises in 25(OH)D3 and 24,25(OH)2D3 levels, but no increase in 1,25(OH)2D levels. After 1,25(OH)2D3 treatment, 25(OH)D3 levels were unchanged but still showed seasonal variation in some patients, suggesting a lack of feedback control by 1,25(OH)2D3. Levels of 24,25(OH)2D3 were not significantly different from baseline values. Levels of 1,25(OH)2D increased initially then dropped to pretreatment levels or lower. Normal 1,25(OH)2D levels and reduced 24,25(OH)2D3 levels with the loss of seasonal variation suggests in our patients that the kidney was able to maintain 1,25(OH)2D levels at the expense of 24,25(OH)2D3 levels, presumably to preserve calcium homeostasis.

Effect of 24,25(OH)2D3 on PTH levels and bone histology in dogs with chronic uremia

Controversy exists as to whether 24,25(OH)2D3 has a direct inhibitory effect on parathyroid hormone (PTH) secretion. Therefore, the present investigation examined the effect of long-term administration of 24,25(OH)2D3 on immunoassayable PTH levels (iPTH) and bone histology in dogs with chronic renal failure. Chronic renal failure was produced in 16 dogs, half of which served as controls whereas the other half received 2.5 micrograms/day of 24,25(OH)2D3, orally. Serum iPTH, serum total, ionized calcium, serum phosphorus, and creatinine were followed at weekly or biweekly intervals in both groups. Also, creatinine clearances, serum levels of 25(OH)D3, 24,25(OH)2D3, and 1,25(OD)2D3 and the intestinal absorption of calcium were measured. After 1 year of chronic renal failure the dogs were sacrificed and rib biopsy specimens were obtained for histological examination and measurement of mineral content. Serum iPTH increased equally in the two dog groups with no effect at any time of 24,25(OH)2D3 treatment, despite a significant increase in the serum levels of 24,25(OH)2D3 and a concomitant decrease of the 1,25(OH)2D3 levels. There was no difference in the levels of serum calcium or in the calcium content of bone. Furthermore, after 8 months of uremia three control dogs were switched to the group treated with 24,25(OH)2D3 and followed for another 7 months. No suppressive effect of administering 24,25(OH)2D3 on the iPTH levels could be demonstrated in these three dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum vitamin D metabolites in younger and elderly postmenopausal women

Previous investigations have suggested that a lower-than-normal serum 1,25(OH)2D is found in elderly women with postmenopausal osteoporosis. We examined the fundamental aspects of this theory by investigating serum vitamin D metabolites in four representative samples of Caucasian women. These included 44 early postmenopausal women divided into two subgroups: fast bone losers, that is, bone loss greater than 3%/year (n = 20), and "physiological" bone loss (n = 24); and 28 70-year-old women divided into two subgroups: with and without osteoporotic fractures. Serum 1,25(OH)2D concentrations were virtually the same in all groups thus contradicting the previous reports of low 1,25(OH)2D in elderly women. Furthermore, mean 25OHD and 24,25(OH)2D did not differ between the groups. We conclude that 1,25(OH)2D is unlikely to be significant in the development or treatment of a majority of women with postmenopausal osteoporosis.