Effect of aluminum on normal and uremic rats: tissue distribution, vitamin D metabolites, and quantitative bone histology

The effects of intraperitoneal aluminum chloride (1.5 mg aluminum/kg/day for 9 weeks) were studied in normal and uremic rats. Parameters measured included tissue aluminum, serum vitamin D metabolites, and quantitative bone histology. Aluminum administration increased tissue concentrations of this metal in uremic and nonuremic animals. Bone aluminum concentrations were higher in uremic rats (121 +/- 27 mg/kg compared to 47 +/- 4), whereas liver values were higher in the nonuremic group (175 +/- 47 mg/kg compared to 100 +/- 36). Serum concentrations of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D were reduced in uremia, but aluminum was without apparent effect on any vitamin D metabolite. Aluminum, in the doses administered, caused no skeletal changes in nonuremic animals. Some uremic, non-aluminum-treated rats developed osteomalacia and marrow fibrosis. However, osteomalacia was more severe and the osteoclast count was higher in the uremic, aluminum-treated rats. In this group of animals the mineral apposition rate was reduced at the metaphyseal endosteum but increased at the periosteum, indicating different control mechanisms at the two sites.     

Effects of dietary supplementation of calcium and vitamin don bone growth in growing male rats

Effects of dietary supplementation of calcium (Ca) and vitamin D(D) on bone growth in growing male rats were investigated. We performed this study using D-deficient rats of 3-month-old. In the experiment 1, the D-deficient rats were fed either low-Ca (0.22% Ca) or high-Ca (1.20% Ca) diets with oral supplementation of different amounts of D₃ (0, 0.7, 7 or 70 IU/week) for 28 days. In the dxperiment 2, the D-deficient rats were fed diets containing different concentrations of Ca (0.22, 0.44, 0.88 or 1.20%) with oral D₃ supplementation of either low-dose (0.7 IU/week) or relatively high-dose (70 IU/week) for 28 days. After the feeding period, plasma levels of Ca, 1α, 25 (OH)₂D₃, PTH, bone Gla protein were measured. Bone ash weight, bone mineral density, mechanical bone strength were also measured. In the both experiments, the plasma levels of PTH decreased to the normal levels in response to the increased amounts of dietary Ca intakes as well as D supplementation. In contrast, the bone markers increased to the respective normal levels in response to the increased amounts of dietary Ca intakes as well as D supplementation. In the experiments 1 and 2, a high correlation between the plasma levels of PTH and the bone markers was observed. These results suggest that both dietary Ca and D supplementation may affect bone growth in growing rats by controlling PTH secretion.     

Effects of vitamin D metabolites on healing of low phosphate, vitamin D-deficient induced rickets in rats

A model of low-phosphate, vitamin D-deficient rachitic rats was used to compare the effects of 1 alpha(OH)D3, 1,25(OH)2D3, and 24,25(OH)2D3 on cartilage and bone. The rats were maintained for 3 weeks on a high-calcium, low-phosphate, vitamin D-deficient diet, during which period they developed severe rickets. The rachitic rats were injected for 2 or 3 consecutive days with a physiologic dose of either metabolite. Other littermates were given a single dose of 50,000 IU of cholecalciferol in combination with a normal diet. Samples of cartilage fluid (Cfl) and of blood were removed prior to sacrifice for biochemical studies of some parameters of calcification. These parameters were correlated with the results of light and electron microscopic studies of the growth plate cartilage and bone. Treatment with 1 alpha (OH)D3 or with 1,25(OH)2D3, in spite of increasing Ca and P levels in the Cfl, induced only partial healing of the rickets. In contrast, 24,25(OH)2D3 or vitamin D with a normal diet resulted in complete morphologic and biochemical healing of the rickets. Transmission electron microscopic (TEM) studies have shown partial mineralization of the wide hypertrophic zone of the growth plate following treatment with 1 alpha(OH)D3 or with 1,25(OH)2D3. Mineralization was more complete with 24,25(OH)2D3 treatment. The results of this study emphasize the importance of 24,25(OH)2D3 for normal endochondral bone formation and mineralization.     

Role of vitamin D in maternal skeletal changes during pregnancy and lactation: A histomorphometric study

Summary The effect of vitamin D on bone changes during the reproductive cycle in female rats has been investigated. One group of female rats was maintained on a vitamin D-deficient diet and another group on a vitamin D-replete diet from weaning. Both groups were mated with normal males and changes in their bones were determined histomorphometrically during pregnancy, lactation, and after weaning. All vitamin D-deficient rats had bone changes typical of rickets. Pregnancy caused significant reductions in mineralized tissue of trabecular and cortical bone in the vitamin D-deficient rats. Lactation caused further significant reductions in mineralized tissues of cortical and trabecular bone in both the vitamin D-deficient and vitamin D-replete animals, with the greatest changes seen at weaning. Some restoration of mineralized tissues occurred following weaning. There was an increase in tetracycline-labeled bone surface in the vitamin D-replete animals during lactation, likely due to an increase in bone formation rates. In the vitamin D-deficient animals during lactation, there was a decrease in tetracyclinelabeled bone surface, likely due to severely depressed bone mineralization. These results indicate that the mobilization of calcium from bone to maintain pregnancy and lactation occurs by a mechanism independent of vitamin D.     

Bioavailability of calcium from oyster shell electrolysate and DL-Calcium lactate in vitamin D-replete or vitamin D-deficient rats

Bioavailability of calcium (Ca) from oyster shell electrolysate (Active Absorbable Ca: AACa) and DL-Ca lactate in rats was investigated. Plasma Ca metabolism, bone mineral density and vitamin D-deficient rats were measured and compared each other. Vitamin D-deficient rats were fedad libitum a vitamin D-free diet containing 0.44 % Ca or 1.20 % Ca adjusted with either AACa or DL-Ca lactate with or without oral supplementation of physiological dose (10 IU/rat/day) of vitamin D₃ for 28 days. During and after feeding, concentrations of Ca, phosphorus, parathyroid hormone (PTH), 25-hydroxyvitamin D₃ (25-OH-D₃), 1α, 25-dihydroxyvitamin D₃ [1, 25(OH)₂D₃] and alkaline phosphatase (Alp) activity in plasma were measured. Furthermore, femoral Ca and phosphorus contents, mineral density and mechanical strength were also measured. Despite of the differences of contents and chemical forms of Ca in diets, all the groups showed prompt and complete recoveries in both Ca and vitamin D malnutritions under vitamin D-replete condition and there was no significant difference among all the groups in increases of body weight gains and plasma Ca levels, and in decreases of plasma PTH level and Alp activity. In contrast, the groups fed the same diets under vitamin D-deficient condition showed no significant recoveries in both plasma Ca metabolism and bone mineralization although Ca bioavailability of AACa appeared to be slightly better than that of DL-Ca lactate. These results suggest that bioavailability of Ca from AACa and DL-Ca lactate are substantially equal in increasing plasma Ca levels, bone mineral density and mechanical strength in both vitamin D-replete and vitamin D-deficient rats.     

Aluminum metabolism in rats: effects of vitamin D, dihydrotachysterol, 1,25-dihydroxyvitamin D and phosphate binders

In order to study the effects of vitamin D on aluminium balance when different forms of vitamin D and phosphate binders are used simultaneously for therapeutic purposes, 30 Sprague-Dawley weanling rats, weighing 44-66 g, were randomly assigned to 5 groups: (A) control, (B) aluminum hydroxide, (C) dihydrotachysterol at 16 micrograms/kg/day, (D) 1,25-dihydroxyvitamin D at 16 ng/kg/day and (E) vitamin D at 2,000 IU/kg/day. Aluminum hydroxide (60 mg/kg/day) in the feed was provided to all except the control group. The vitamin D or metabolites were fed by stomach tube daily for a period of 10 days. At the end of the study, the mean (+/- SEM) serum aluminum concentration, as determined by flameless atomic absorption spectrophotometry, was 5.0 +/- 2.4 micrograms/l; there were no significant differences in these results between groups. During the last three days of the study, 24-hour urine and stool collections were made with the usual precautions against trace mineral contamination. The means (+/- SEM) of aluminum balances for groups A, B, C, D and E were -388 +/- 261, 1,121 +/- 331; 2,316 +/- 304; 2,387 +/- 245, and 1,968 +/- 337 micrograms/day, respectively. We conclude that at therapeutic doses of aluminum hydroxide and vitamin D or its metabolites, hyperaluminemia was not observed. However, the positive aluminum balances imply retention, and the use of vitamin D, especially its potent metabolites dihydrotachysterol and 1,25-dihydroxyvitamin D, intensified this risk.     

Relative effectiveness of vitamin D metabolites in increasing bone mineral solubility

Weanling rats were given a vitamin D-deficient diet containing 1.4% calcium and 1.0% phosphorus. After 4 weeks these deficient animals were injected for 7 days with selected doses of one of the following vitamin D metabolites: 25(OH)D3, 1,25(OH)2D3, 24,25(OH)2D3, 25,26(OH)2D3 or the ethanol vehicle. A vitamin D-replete group was placed on the same diet but injected with 50 IU of vitamin D3 once a week for the entire 5-week period. By the use of a modified Ussing chamber [1], the measurements of calcium fluxes into and from the rat calvaria were possible. These data enabled the apparent mineral solubilities to be derived. After 5 weeks on this diet the vitamin D-deficient rats had low levels of serum calcium (1.41 mM) and decreased mineral solubility when compared to the vitamin D-replete group. The apparent solubility of the bone mineral increased toward the vitamin D-replete level in calvaria from vitamin D metabolite-treated rats. However, these changes did not directly reflect the alterations in the level of serum calcium. At any given dose level, 1,25(OH)2D3 was the most effective metabolite in increasing serum calcium. In fact, the high dose (250 pmoles/day) was hypercalcemic. Next in effectiveness was 25(OH)D3. These two metabolites were equally effective in increasing mineral solubility. At a 10 times higher dose, the 24,25(OH)2D3 metabolite was able to normalize serum calcium and improve but not normalize mineral solubility. At the high dose (260 pmoles/day), the 25,26(OH)2D3 metabolite caused no effect on mineral solubility and minimal increases in serum calcium.     

Effect of dietary calcium supplementation with lactose on bone in vitamin D-deficient rats

The relationship between plasma calcium and bone length, chemical and histomorphometric bone parameters was studied in vitamin D-deficient rats in order to determine whether the effects of vitamin D on bone could be attributed to the effect of vitamin D on serum calcium. Plasma calcium was varied over a wide range of dietary manipulation. Four groups of vitamin D-deficient rats were given for 6 weeks: a vitamin D-deficient diet (D⁻, n = 6), the D⁻-diet with calcium supplementation (D⁻Ca⁺, n = 6), the D⁻Ca⁺-diet with lactose substituted for dextrose (D⁻Ca⁺lac, n = 6) or a normal diet (D⁺, n = 8). After 6 weeks the mean plasma calcium concentrations were 6.1 ; 7.0; 9.8; and 10.4 mg/dl, respectively. In the vitamin D-deficient rats (groups D⁻, D⁻Ca⁺, D⁻Ca⁺lac) plasma calcium was correlated with bone length, bone ash, volumetric density of osteoid in the metaphysis of the tibia, and volumetric density of trabecular bone in the same bone section. In the D⁻Ca⁺lac group these bone parameters approximated the values of the D⁺ group, but were still significantly lower. It is concluded that in vitamin D-deficient rats longitudinal bone growth, bone mineral content and bone histomorphometry can be brought close to normal by supplying additional dietary calcium with lactose, without vitamin D repletion. The study does not exclude the possibility that residual amounts of vitamin D are required to obtain this effect.     

Studies on the role of vitamin D in early skeletal development,mineralization, and growth in rats

Summary The role of vitamin D in early skeletal development was studied by measuring serum calcium and phosphorus, osseous tissue quantity and mineralization, and endochondral bone elongation in rat fetuses and pups from vitamin D-replete and vitamin D-deficient mothers. At the 20th day of pregnancy there was a slight, yet significant, increase in the amount of osteoid on trabecular bone surfaces in fetuses from vitamin D-deficient mothers. The fetal bones otherwise appeared normal in spite of severe skeletal changes in the vitamin D-deficient mothers. After parturition, the importance of vitamin D in skeletal development becomes progressively more obvious. Serum calcium levels were slightly, yet significantly, lower in vitamin D-deficient than in vitamin D-replete pups and these levels continued to fall in the vitamin D-deficient pups through lactation and after weaning. At 3 days postpartum, there was a small, yet significant, increase in the amount of osteoid on bone surfaces of the vitamin D-deficient pups. The relative amounts of osteoid in the vitamin D-deficient pups continued to increase through lactation and after weaning when compared with vitamin D-replete pups. By the 14th day of lactation and at later periods, there were significant reductions in metaphyseal mineralized tissues in the vitamin D-deficient pups when compared with the vitamin D-replete pups. At weaning and after weaning, there were substantial increases in growth plate thickness and decreases in longitudinal bone growth in the vitamin D-deficient pups when compared with the vitamin D-replete pups. The results from this study indicate that vitamin D does not appear to play a major role in fetal skeletal development. However, after birth, vitamin D becomes progressively more important with age for normal bone development, mineralization, and endochondral growth.     

Bone maturation in the vitamin D,phosphate deficient rat and the response to acid loading

Summary Vitamin D and phosphate deficiency were produced in rats in order (a) to evaluate the degree of bone mineral and matrix maturation using a bromoform/toluene density gradient technique; and (b) to compare the aforementioned bone maturational changes due to vitamin D and phosphate deprivation to those produced with superimposed severe acidosis. Rats were fed a diet deficient in vitamin D and phosphorus (0.2%) from 3 weeks through 7 weeks of age. To examine the additional contribution of dietary calcium, we gave one-half of the animals either a low (0.06%) or high (1.3%) calcium diet. Following the 4 weeks of vitamin D deficiency, one-half of each group was given 1.8% NH₄Cl in the drinking water for 4 succeeding days to induce an acute, severe acidosis. The degree of bone maturation was quantitated via bromoformtoulene density gradient fractionation; total mineral and hydroxyproline (collagen) levels were quantitated as well. The vitamin D-deficient rats deprived of adequate dietary phosphate responded by conserving phosphorus, and as a consequence total bone phosphorus levels were maintained within that level for control rats. This conservation was independent of calcium intake but was extremely sensitive to acute acid loading, where a significant reduction in total bone phosphorus was noted. The bone maturational profile obtained from the vitamin D-phosphate deficient rats, however, revealed a significant accumulation of less mature or dense bone collagen and mineral with a corresponding decrease in the most mature or dense moieties. In contrast to the reduction of the total bone phosphorus content by acute acidosis, the skeletal collagen-mineral maturational profile was not significantly affected by the short-term systemic acidosis. The observed retardations in the bone collagen and mineral maturation of the vitamin D-deficient, phosphate-deprived state provide an additional observation which may well relate to the progressive osteopenia documented in states of chronic, mild acidosis.     

The biological activity of synthetic 25,26-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol in vitamin D-deficient rats

The biological activity of synthetic 24,25 and 25,26 diOHD3 was studied in vitamin D-deficient rats. The purpose of this study was to investigate the influence of small doses of both metabolites (0.125–0.250 μg) upon intestinal calcium transport and bone calcium mobilization. Both metabolites were able to increase calcium absorption in rats maintained on a calcium-deficient diet, but failed to do it in rats on a normal calcium diet. Bilateral nephrectomy suppressed this effect. The “bone calcium mobilization” of both derivatives was measured in vitamin D and calcium- or phosphorus-deprived rats after one intravenous dose. When serum calcium was initially low, 24,25 and 25,26 diOHD3 increased serum calcium moderately, but the increment was only significant with 24,25 diOHD3. When serum calcium was normal before the injection, both metabolites decreased serum calcium significantly, and the decrease was greater with 24,25 diOHD3. Intraperitoneal administration of the metabolites for 5 consecutive days produced a significant increase of calcium in serum and bone ash.     

The biological activity of synthetic 25,26-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol in vitamin D-deficient rats

The biological activity of synthetic 24,25 and 25,26 diOHD3 was studied in vitamin D-deficient rats. The purpose of this study was to investigate the influence of small doses of both metabolites (0.125–0.250 μg) upon intestinal calcium transport and bone calcium mobilization. Both metabolites were able to increase calcium absorption in rats maintained on a calcium-deficient diet, but failed to do it in rats on a normal calcium diet. Bilateral nephrectomy suppressed this effect. The “bone calcium mobilization” of both derivatives was measured in vitamin D and calcium- or phosphorus-deprived rats after one intravenous dose. When serum calcium was initially low, 24,25 and 25,26 diOHD3 increased serum calcium moderately, but the increment was only significant with 24,25 diOHD3. When serum calcium was normal before the injection, both metabolites decreased serum calcium significantly, and the decrease was greater with 24,25 diOHD3. Intraperitoneal administration of the metabolites for 5 consecutive days produced a significant increase of calcium in serum and bone ash.     

The effect of vitamin D deficiency on rat bone lipid composition

Vitamin D and phosphate deficiency has been shown previously to result in an accumulation of calcium acidic phospholipid phosphate complexes in the epiphysis of immature rats and to increase the cholesterol and decrease the lysophosphatide content throughout bone. To define the effects of vitamin D deficiency and those of combined vitamin D and phosphate deficiency, the lipid composition of the bones of second generation rachitic rats, raised on a diet that was vitamin D deficient was compared to that of normal animals fed a vitamin D-repleted diet and to previously studied vitamin D and phosphate-deficient rats. Animals raised on the vitamin D-deficient diet in utero and during postfetal life were serologically quite different from controls. These animals were significantly hypocalcemic and had no detectable vitamin D metabolites. Similar to the previously studied phosphate-deficient rachitic animals, the vitamin D-deficient animals had significantly elevated total lipid contents (weight percent lipid per demineralized dry weight) throughout their bones as compared to controls (epimetaphysis 9.6 vs 6.7 (P less than or equal to 0.03), diaphysis 6 vs 2 (P less than or equal to 0.01), calvaria 6.1 vs 2.4 (P less than or equal to 0.002). Similar to the vitamin D and phosphate-deficient animals, the second generation vitamin D-deficient rat bones had elevated cholesterol and reduced lysophosphatide contents. Complexed acidic phospholipids were not significantly elevated in the vitamin D-deficient animal bones. The data suggest that the lipid changes seen in these animals are due to vitamin D deficiency and not to phosphate deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)     

Restoring and maintaining bone in osteopenic female rat skeleton: I. Changes in bone mass and structure.

This experiment contains the crucial data for the lose, restore, and maintain (LRM) concept, a practical approach for reversing existing osteoporosis. The LRM concept uses anabolic agents to restore bone mass and architecture (+ phase) and then switches to an agent with the established ability to maintain bone mass, to keep the new bone (+/- phase). The purpose of this study was to learn whether switching to an agent known chiefly for its ability to maintain existing bone mass preserves new bone induced by PGE2 in osteopenic, estrogen-depleted rats. The current study had three phases, the bone loss (-), restore (+), and maintain (+/-) phases. We ovariectomized (OX) or sham ovariectomized (sham-OX) 5.5-month-old female rats (- phase). The OX rats were treated 5 months postovariectomy with 1-6 mg PGE2 per kg/day for 75 days to restore lost cancellous bone mass (+ phase), and then PGE2 treatment was stopped and treatment began with 1 or 5 micrograms/kg of risedronate, a bisphosphonate, twice a week for 60 days (+/- phase). During the loss (-) phase, the cancellous bone volume of the proximal tibial metaphysis in the OX rat fell to 19% of initial and 30% of age-matched control levels. During the restore (+) phase, the cancellous bone volume in OX rats doubled. When PGE2 treatment was stopped, however, and no special maintenance efforts were made during the maintain (+/-) phase, the PGE2-induced cancellous bone disappeared. In contrast, the PGE2-induced cancellous bone persisted when the PGE2 treatment was followed by either a 1 or 5 micrograms treatment of risedronate per kg given twice a week for 60 days during the maintain (+/-) phase. The tibial shaft demonstrated very little cortical bone loss during the loss (-) phase in OX rats. The tibial shaft cortical bone fell some 8%. During the restore (+) phase, new cortical bone in OX rats increased by 22%. When PGE2 treatment was stopped and nothing was given during the maintain (+/-) phase, however, all but the PGE2-induced subperiosteal bone disappeared. In contrast, when PGE2 treatment was stopped and 1 micron risedronate per kg twice a week for 60 days was administered during the maintenance (+/-) phase, the PGE2-induced subperiosteal bone and some of the subendocortical bone and marrow trabeculae persisted.(ABSTRACT TRUNCATED AT 400 WORDS)     

A morphometric investigation of the duodenal mucosa of normal, vitamin D-deficient, and vitamin D-replete rats

Light and electron microscopy were utilized to determine differences in morphology and size in duodenal villi and microvilli from normal, vitamin D-deficient, and vitamin D-replete rats. An increase in villus diameter and surface area was observed in vitamin D-deficient rats. Administration of vitamin D reversed the increase in diameter but the height of villi increased resulting in longer, thinner villi without a significant change in surface area. A decrease in microvillus surface area seen in vitamin D-deficient animals was reversed by the administration of vitamin D.     

Relative effectiveness of vitamin D metabolites in increasing bone mineral solubility

Summary Weanling rats were given a vitamin D-deficient diet containing 1.4% calcium and 1.0% phosphorus. After 4 weeks these deficient animals were injected for 7 days with selected doses of one of the following vitamin D metabolites: 25(OH)D₃, 1,25(OH)₂D₃, 24,25(OH)₂D₃, 25,26(OH)₂D₃ or the ethanol vehicle. A vitamin D-replete group was placed on the same diet but injected with 50 IU of vitamin D₃ once a week for the entire 5-week period. By the use of a modified Ussing chamber [1], the measurements of calcium fluxes into and from the rat calvaria were possible. These data enabled the apparent mineral solubilities to be derived. After 5 weeks on this diet the vitamin D-deficient rats had low levels of serum calcium (1.41 mM) and decreased mineral solubility when compared to the vitamin D-replete group. The apparent solubility of the bone mineral increased toward the vitamin D-replete level in calvaria from vitamin D metabolite-treated rats. However, these changes did not directly reflect the alterations in the level of serum calcium. At any given dose level, 1,25(OH)₂D₃ was the most effective metabolite in increasing serum calcium. In fact, the high dose (250 pmoles/day) was hypercalcemic. Next in effectiveness was 25(OH)D₃. These two metabolites were equally effective in increasing mineral solubility. At a 10 times higher dose, the 24,25(OH)₂D₃ metabolite was able to normalize serum calcium and improve but not normalize mineral solubility. At the high dose (260 pmoles/day), the 25,26(OH)₂D₃ metabolite caused no effect on mineral solubility and minimal increases in serum calcium.     

Studies on the role of 24-hydroxylation of vitamin D in the mineralization of cartilage and bone of vitamin D-deficient rats

Summary To test the importance of 24-hydroxylation of vitamin D₃ on bone mineralization, rat pups born to vitamin D-deficient females were given either 25-hydroxyvitamin D₃ or 24,24-difluoro-25-hydroxyvitamin D₃ for 16 days beginning at the time of weaning. Following such treatment analysis of blood samples revealed no detectable 24R,25-(OH)₂D₃ and 1,25-(OH)₂D₃ in the rats given the difluoro compound while revealing the expected 24,24-difluoro-25-hydroxyvitamin D₃ and 24,24-difluoro-1,25-dihydroxyvitamin D₃. The rats given 25-hydroxyvitamin D₃ had the expected levels of 25-hydroxyvitamin D₃, 24,25-dihydroxyvitamin D₃, and 1,25-dihydroxyvitamin D₃. Following sacrifice at day 17, postweaning bone mineralization and modeling were studied in long bones using histological methods. Bones taken from vitamin D-deficient rats at the beginning and end of the experimental period had lesions typical of rickets. These included wide growth plates, excessive amounts of osteoid, and metaphyseal fibrosis. Following treatment with either 25-hydroxyvitamin D₃ or 24,24-difluoro-25-hydroxyvitamin D₃, bone mineralization returned to normal. Growth plate widths and the amount of osteoid on bone surfaces were both substantially reduced and to a similar degree in both treatment groups. Normal cartilage core formation and trabecularization of the metaphyseal primary spongiosa were also restored to a similar degree in both groups. In effect, no difference was observed in any bone parameter studied between the 25-hydroxyvitamin D₃- and the 24,24-difluoro-25-hydroxyvitamin D₃-treated animals. These results provide strong evidence that 24-hydroxylation of the vitamin D molecule plays little or no role in the modeling and mineralization of bone.     

Effects of vitamin D3 analogues on parathyroid hormone secretion and calcium metabolism in vitamin D-deficient rats

22-Oxa-1α, 25-dihydroxyvitamin D₃ (OCT) and 2β-(3-Hydroxypropoxy)-1α, 25-dihydroxyvitamin D₃ (ED-71) are novel synthetic vitamin D₃ analogues. In order to examine their calcemic actions on intestine and bone, we have investigated the effects of OCT and ED-71 on intestinal Ca transport, bone mobilization and plasma parathyroid hormone (PTH) level in vitamin D-deficient rats. The vitamin D-deficient rats were intravenously given either 6.25μg/kg or 0.2μg/kg of 1,25-D₃, OCT or ED-71 and theirplasma Ca levels and intestinal Ca transport were measured periodically. At a high dose, 1,25(OH)₂D₃ and ED-71 showed a strong biphasic stimulation of intestinal Ca transport and bone mobilization, and reduced the plasma PTH levels to the normal level completely. On the other hand, OCT failed to suppress the PTH secretion although it exerted first phase action on the both intestinal Ca transport and bone mobilization in vitamin D-deficient rats. The reason why OCT failed to suppress the PTH secretion even at a high dose, has not yet been clarified, but it may be at least in part due to its weak calcemic action and short half-life in plasma.     

The role of vitamin D in the medullary bone formation in egg-laying Japanese quail and in immature male chicks treated with sex hormones

The effect of vitamin D3 on medullary bone formation was investigated in egg-laying Japanese quail and in immature male chicks treated with sex hormones. When laying quail were fed a vitamin D-deficient diet for 16 days, their eggshell weights and egg production rate were markedly reduced in a time-dependent manner with a significant decrease in plasma calcium and 25-hydroxyvitamin D3 levels. The calcium content of the medullary bone of femurs decreased markedly with the progress of vitamin D deficiency, whereas that of the cortical bone remained unchanged. Quantitative histological examination also showed that the area of the mineralized portion of medullary bone in quail that were fed the vitamin D-deficient diet markedly decreased compared with that in the control laying quail, whereas the total area of the mineralized and unmineralized portions of medullary bone in the bone marrow cavity increased moderately. Daily administration of vitamin D3 (0.75 microgram/day) to the vitamin D-deficient quail increased the mineralization of medullary bone as early as day 4. Daily administration of both estradiol (0.3 mg/day) and testosterone (0.9 mg/day) for 3 weeks to immature male chicks induced an apparent hypercalcemia and matrix formation of medullary bone, regardless of the vitamin D status of the chicks. Mineralization of medullary bone was observed only when vitamin D3 was administered together with the sex hormones. These results suggest that vitamin D3 is directly involved in the mineralization of medullary bone in birds.     

The effect of short-term treatment with vitamin D metabolites on bone lipid and mineral composition in healing vitamin D-deficient rats

Vitamin D deficiency is known to cause alterations in the lipid and mineral components of bone and cartilage. In this study, second generation, normal phosphatemic, vitamin D-deficient rats, treated with low and high doses of three different vitamin D metabolites were sacrificed 24 h after treatment and their bones analyzed in order to determine which metabolites were most effective in altering the lipid composition. In the untreated vitamin D-deficient rats, tissues undergoing endochondral ossification (epimetaphyses), periosteal and endosteal bone formation (diaphyseal bone), and intramembranous bone formation (calvaria) all contained lower amounts of complexed acidic phospholipids, as well as decreased amounts of mineral. Twenty-four hours following treatment, the complexed acidic phospholipid content was significantly increased relative to both untreated and normal (vitamin D-replete) animals, the greatest increases occurring in animals treated with 1,25-dihydroxyvitamin D. All metabolites tested altered histomorphometric and/or mineral parameters, but only 1,25-dihydroxyvitamin D, in low and high doses, significantly increased the content of the complexed acidic phospholipids in all tissues studied. High doses of other metabolites increased complexed acidic phospholipid content in some tissues, perhaps due to their conversion to 1,25-dihydroxyvitamin D. Linear relationships between serum 1,25-dihydroxyvitamin D levels and tissue complexed acidic phospholipid content are reported. It is suggested that one way in which this metabolite may directly contribute to calcification is by facilitating formation of lipids involved in this process.