Effect of 1 alpha-hydroxyvitamin D3 on cancellous bone matrix. An experimental study on adult rats

Effect of 1 alpha-vitamin D3 on bone strength and composition in growing rats with and without corticosteroid treatment

The effects of 1 alpha-vitamin D3 were studied for 6 months in 2-month-old male and female rats on a moderately low calcium diet with or without low-dose prednisolone treatment. Both cortical bone mechanical and biochemical properties were examined. Femoral bone specimens were subjected to torsional loading tests. With age, bone strength and stiffness increased in both sexes, accompanied by an increased degree of mineralization (bone ash and calcium concentrations). During growth, strength and stiffness increased more in male than in female rats. When 1 alpha-vitamin D3 (0.5 micrograms/kg/day) was given alone, bone mechanical competence improved significantly whereas insulin-like growth factor-I (IGF-I) and calcium concentrations in the bone matrix were significantly reduced. Treatment with low-dose prednisolone (0.5 mg/kg/day) alone did not influence bone mechanical properties compared with intact control rats (without prednisolone) although a significant reduction in calcium concentration and an increased phosphorus concentration were measured. A combined therapy with prednisolone and 1 alpha-vitamin D3 significantly increased bone strength, toughness, and stiffness compared with control bones. Both mineralization degree (ash and calcium concentration) and IGF-I concentration were decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

1,25 dihydroxyvitamin D3 alone or in combination with parathyroid hormone does not increase bone mass in young rats

Parathyroid hormone (PTH) alone is known to increase bone mass, but clinical studies of osteoporotic men suggest that when 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) is given in combination with PTH, the effect on bone growth is enhanced. To determine if 1,25(OH)2D3 alone would stimulate bone growth, young male rats were given daily subcutaneous injections of either vehicle or 2.5, 5, 10, or 20 ng 1,25(OH)2D3 per 100 g body weight for 30 days. To determine if 1,25(OH)2D3 would augment the PTH anabolic response, rats were given daily subcutaneous injections of either vehicle for 12 days; or 4 micrograms/100 g hPTH alone or in combination with 5 ng/100 g 1,25(OH)2D3; or 8 micrograms/100 g hPTH alone or in combination with 5 ng/100 g 1,25(OH)2D3. Calcium (Ca), dry weight (DW), and hydroxyproline (Hyp) of the distal femur; the rate of mineralization in the metaphysis of the proximal tibia; and serum calcium and phosphate were measured. Low normocalcemic doses of 1,25(OH)2D3 did not significantly stimulate bone growth. 1,25(OH)2D3 did not augment the PTH-stimulated anabolic effect in young male rats. Low doses (2.5 and 5 ng) of 1,25(OH)2D3 were not hypercalcemic, and there was no increase in total bone calcium or dry weight although the 5 ng dose increased trabecular bone calcium. 1,25(OH)2D3 at 10 and 20 ng increased trabecular bone DW and Hyp, but mineralization was impaired and rats were hypercalcemic. 1,25(OH)2D3 in combination with PTH did not augment the PTH stimulation of bone growth as trabecular and cortical bone Ca, DW, and HYP were not increased in rats given both hPTH and 1,25(OH)2D3 compared with values for rats treated with hPTH alone.

Effect of 1 alpha-hydroxyvitamin D3 on osteoporosis induced by immobilization combined with ovariectomy in rats

The effect of low-dose 1 alpha-hydroxyvitamin D3 [1 alpha(OH)D3] on experimental osteoporosis in rats induced by a combination of hemicordotomy and ovariectomy was evaluated. 1 alpha(OH)D3 (0.1 microgram/kg 1 alpha(OH)D3 three times a week) increased the femur score and photo-density. The administration of 1 alpha(OH)D3 also significantly increased the dry weight and ash weight of the bone. Histomorphometry revealed a significant decrease of bone resorption by the administration of 1 alpha(OH)D3. Significant decreases in 45Ca accretion rate and 14C-proline uptake were also observed. Bone formation in the 1 alpha(OH)D3 treated group was thought to decrease following the decrease of bone resorption.

Stimulation of undermineralized matrix formation by 1,25 dihydroxyvitamin D3 in long bones of rats

We previously reported that pharmacologic doses of 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) given for 2-3 days, inhibited osteoblastic collagen synthesis in young rats. In this study, we tested the effects of 5, 25, and 125 ng of 1,25(OH)2D3 injected subcutaneously into 6-week-old rats for 12 or 18 days. In rats given 125 ng, cortical bone of distal half femurs exhibited decreased calcium (Ca) content but dry weight and hydroxyproline (Hyp) content were no different from control. Trabecular bone Ca was not different from control but dry weight and Hyp were increased. When cortical and trabecular bone were combined, there was a decrease in Ca, an increase in Hyp, and a 50% decrease in Ca:Hyp. Fluorescent labels given after 8 days of treatment were either diffuse or absent in calcified sections from rats given 125 ng, indicating impaired mineralization. The 25 and 125 ng doses produced hypercalcemia with normal serum phosphate. There was a dose-related increase in serum immunoreactive bone gla protein (BGP) and serum 1,25(OH)2D3 and a decrease in serum 25(OH)D3. At the 5 ng dose, no adverse effects were seen on body growth. With 25 ng and 125 ng, growth was inhibited. Increased serum urea nitrogen and histologic evidence of nephrocalcinosis occurred at the 125 ng dose. When 125 ng was given for 12 days and then withdrawn for 6 days, systemic toxicity decreased and bone Hyp and Ca increased so that Ca:Hyp remained low and comparable to that of rats treated with 1,25(OH)2D3 continuously.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of 1 alpha-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 on experimentally induced heterotopic ossification in rats

We report the effects of 1 alpha-OH-D3 and 24,25(OH)2D3, either alone or combined, on new bone formation induced by demineralized cortical bone matrix transplanted extraskeletally to the abdominal muscle wall in rats. 1 alpha-OH-D3 was administered orally in dosages of 0.1 microgram, 24,25(OH)2D3 in dosages of 0.2 micrograms, and, in the combined procedure, in the same dosages as mentioned above per day and rat. The amount of induced new bone in respect of organic matter, mineral content and 45Ca activity increased in all treatment groups, compared with controls. The differences between the groups treated separately with 1 alpha-OH-D3 or 24,25(OH)2D3 were insignificant. The differences in the combined treatment group were not so profound, but differed considerably compared with controls. However, 1 alpha-OH-D3 showed more prominent effects on the mineralization of implanted grafts, while 24,25(OH)2D3 especially promoted the production of organic material of the newly formed bone.

Effects of 1,25-dihydroxycholecalciferol on fracture healing. Calcium, phosphate, and zinc in callus and serum

The incorporation of calcium, phosphate, and zinc into the callus of closed tibial fractures was studied in adult rats fed a standard diet. Low doses (60 ng/kg per day) of 1,25(OH)2D3 5 days a week greatly increased early callus mineralization. This was not related to an increased serum calcium-phosphate molar product but rather to a decreased ratio. The incorporation of zinc into callus seemed to be correlated to the mineralization process but not to the 1,25(OH)2D3 administration as such. The question of a direct, indirect, or a complex role of 1,25(OH)2D3 in bone formation and mineralization is discussed.