Somatostatin inhibits duodenal calcium transport mediated by 1,25-dihydroxyvitamin D3 in perfused duodena from normal chicks

We have reported that physiological dose (30pM-650pM) of 1,25-dihydroxyvitamin D₃[1,25(OH)₂D₃] increased the unidirectional movement of⁴⁵Ca²⁺ from the lumen to the venous effluent within a few minutes in perfused duodena from normal chicks, and hypercalcemia inhibited this rapid stimulatory effect on calcium transport mediated by 1,25(OH)₂ D₃. The purpose of the present study was to determine the effect of somatostatin on calcium transport in chicks. The basal Ca²⁺ transport, in the absence of 1,25(OH)₂ D₃, did not change when 10⁻⁸M to 10⁻⁶M of somatostatin was added to the perfusate. The effect of 1,25(OH)₂D₃ on calcium transport, however, was completely abolished on addtion of 10⁻⁶M somatostatin in the perfusate, and partially blocked on addition of 10⁻⁷M somatostatin and 10⁻⁸M somatostatin had no effect on 1,25(OH)₂ D₃ mediated calcium transport. These results suggest that somatostatin may decrease intestinal calcium transport mediated by the rapid direct action of 1,25(OH)₂ D₃.     

Serum 1,25-dihydroxyvitamin D concentration in hypophosphatemic vitamin D-resistant rickets

Summary Fasting serum 1α,25-dihydroxyvitamin D (1,25-(OH)₂D) levels were measured in 3 groups of hypophosphatemic vitamin D-resistant rickets (VDRR) patients: those untreated; those treated with vitamin D and phosphate; and those treated with 1,25-(OH)₂D₃ and phosphate. In the untreated patients, the mean 1,25-(OH)₂D level was higher than in our age-matched control group. Except for one at 66 pg/ml, individual values were however within normal limits. Long term vitamin D₂ therapy was accompanied by a slight but significant decrease in 1,25-(OH)₂D concentrations; nonetheless the levels remained within the normal range. In the third group of patients, the concentration of 1,25-(OH)₂D rose to supranormal levels when sampling was done 1–3 hours after administration of the hormone, decreasing rapidly to levels below that of normal subjects when the specimens were collected 12–24 hours later. Our data show that an alteration of the vitamin D activation pathway is unlikely to be part of the pathogenic mechanism underlying the VDRR condition. Calcitriol (1α,25-(OH)₂D₃) as Rocaltrol^R in capsules of 0.25 and 0.50 μg was kindly supplied by Dr. Patrick Le Morvan (Hoffmann-La Roche Ltd, Vaudreuil, Que., Canada).     

Interrelation of cortisone and 1,25 dihydroxycholecalciferol on intestinal calcium and phosphate absorption

Summary The interrelation of glucocorticoids and 1,25 dihydroxycholecalciferol (1,25(OH)₂D₃) on intestinal calcium and phosphate absorption was investigated. The active and passive transport of calcium and phosphate was evaluated by thein situ intestinal loop technique. Administration of cortisone resulted in a decrease of the luminal fluid and an increase of the luminal calcium and phosphate concentration. Under active transport conditions, administration of cortisone resulted in a decrease of net calcium absorption through two mechanisms: (1) depressed vitamin D-dependent calcium absorption, (2) increased vitamin D-independent calcium backflux. The enhancement of bidirectional phosphate flux by cortisone was independent of 1,25(OH)₂D₃. An enhancement of water movement by cortisone resulted in an increase of luminal calcium and phosphate concentration which favors the passive diffusion of these ions. Enhanced calcium diffusion by cortisone compensates for the inhibitory effect of cortisone on vitamin D-dependent calcium transport. However, enhanced phosphate diffusion by cortisone is additive to the effect of 1,25(OH)₂D₃.     

Plasma 1,25-dihydroxyvitamin D concentrations in cords,newborns, infants,and children

Summary Plasma 1,25-dihydroxyvitamin D [1,25-(OH)₂-D] was measured in cord serum, newborns, infants, and children. The mean for the values obtained from the six cords was significantly higher than the mean for the older children (6–15 years). The mean for the six newborns (0–1 week) was significantly higher than that for the older children. The mean for the nine infants (1 week-6 months) and the 14 younger children (6 months-6 years) was significantly higher than that for older children. The present study suggests that the perinatal period is associated with a marked increase in 1,25-(OH)₂-D.     

Hypercalcemia associated with increased circulating 1,25 dihydroxyvitamin D in a patient with pulmonary tuberculosis

Summary Studies are described in a 53-year-old man with far-advanced pulmonary tuberculosis who developed transient increases in circulating 1,25 dihydroxyvitamin D (1,25(OH)₂D) and hypercalcemia while on antituberculous treatment. Serial dilution of an extract of the patient's serum obtained while he was hypercalcemic displaced [³H]-1,25(OH)₂D₃ from chick intestinal receptor in a manner identical to authentic 1,25(OH)₂D₃. Serum 25-hydroxyvitamin D (25OHD) was suppressed during the abnormal elevation of serum 1,25(OH)₂D. It is concluded that tuberculosis is another chronic granulomatous disease in which hypercalcemia may result from abnormal metabolism of vitamin D.     

Oral 1,25-dihydroxyvitamin D3 loading test in normal subjects and patients with chronic renal failure under haemodialysis

Summary: The present study was designed to determine the criterion for 1,25-dihydroxyvitamin D₃ (1,25 (OH)₂D₃) loading test in normal subjects and haemodialysis patients. Fourteen normal subjects were administered 1.0 μg of 1,25(OH)₂D₃ per os and serum 1,25(OH)₂D was monitored every hour up to 6 h afterwards under conditions of overnight fasting, and six haemodialysis patients were administered 2.0 μg of 1,25(OH)₂D₃ per os and serum 1,25(OH)₂D was monitored every 2 h up to 12 h afterwards. Peak time of serum 1,25 (OH)₂D varied between 2 and 5 h after administration in normal subjects. However, there was a good correlation between the maximum increment of 1,25(OH)₂D (maxΔ1,25(OH)₂D) and the increment at 4 h after administration (Δ1,25(OH)₂D(4 h)). the peak time of Δ1,25(OH)₂D in six haemodialysis patients was also at 4 h after administration. From these observations, Δ1,25(OH)₂D(4 h) was evaluated in subsequent studies. Twenty-six normal subjects and 24 haemodialysis patients were administered 0.5–2.0 μg of 1,25(OH)₂D₃ per os, according to their bodyweights, under conditions of overnight fasting. Blood samples were drawn for measuring 1,25(OH)₂D prior to and 4 h after administration. Δ1,25(OH)₂D(4 h) showed good correlation with the dose of 1, 25 (OH)2D3 adjusted by bodyweight (ng/kg bodyweight). the ratio of Δ1,25(OH)₂D(4 h) and adjusted dose of 1,25(OH)₂D₃ was more than 2.0 in all normal subjects (range: 1.97?2.89, mean ± SD: 2.38 ± 0.287). Moreover, the ratio of Δ1,25(OH)₂D(4 h) and adjusted dose of 1,25(OH)₂D₃ showed a good reproducibility (CV%= 5.7 Δ 0.32, n=5), and did not depend on the administered dose of 1,25(OH)₂D₃, suggesting that this ratio is a good parameter for the intestinal absorption of 1,25(OH)₂D₃. In haemodialysis patients, the mean ratio of Δ1,25 (OH)₂D(4 h) and adjusted dose of 1,25(OH)₂D₃ was 2.14 Δ 0.489, which was not significantly different from the ratio in normal subjects, suggesting that, fundamentally, there was no impairment of intestinal absorption of 1,25(OH)₂D₃ in these patients. However, low ratios of Δ(4 h) and the dose of 1,25(OH)₂D₃ with low basal levels of 1,25(OH)₂D were observed in some patients (less than 1.5 in four patients), suggesting that there exist haemodialysis patients with malabsorption of 1,25(OH)₂D₃. From these results, the criterion for normal response in 1,25(OH)₂D loading test was proposed, namely, that the ratio of Δ1,25(OH)₂D(4 h) and adjusted dose of 1,25(OH)₂D₃ be more than 2.0.     

Enhanced sensitivity of young suckling rats to the toxic effects of 1,25-dihydroxyvitamin D3

Summary The responses of suckling rat pups of different ages to high doses of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) were determined. Four daily oral doses of 1,25(OH)₂D₃ (2 ng/g body wt) given to 9–13-day-old pups produced severe hypercalcemia 24 h after the last dose (15.52 ± 0.14 mg/dl vs. 10.94 ± 0.15 mg/dl in controls of the same age) and a 9-fold increase in kidney Ca content; the same doses given to 16–20-day-old pups produced only modest hypercalcemia (12.34 ± 0.22 mg/dl vs. 10.57 ± 0.22 mg/dl in controls of the same age) and a 4-fold increase in kidney Ca content. There was no change in serum phosphorus (P) at either age. Six-week-old weaned rats, given the same doses of 1,25(OH)₂D₃, showed neither hypercalcemia nor kidney calcification and thus were protected against the toxic effects of the treatment. The difference in responses of the twoages of suckling pups was also observed with lower doses. Removal of the solid food from the diet of the 16–20-day pups showed that the consumption of solid food, in addition to milk, in this age group was not the cause of the lower serum Ca response. The changes in both serum and kidney Ca after intraperitoneal (i.p.) injections of 1,25(OH)₂D₃ at the same dose in each age group were similar to those observed with oral administration. The time course of the rise in serum Ca following a single dose of 1,25(OH)₂D₃, given either orally or i.p., showed that the hypercalcemia was more pronounced and lasted longer in the 9–13-day pups than in the 16–20-day pups. The results suggest that weaned rats are relatively well protected against hypervitaminosis D and that younger pups gradually develop such protection during the suckling period.     

1,25(OH)2D and 24,25(OH)2D production in the developing kidney

To clarify the state of vitamin D production by the developing kidney, firstly, we measured serum levels of 1,25(OH)₂D and 24,25(OH)₂D in humans of different ages (pregnant and nonpregnant women, adult males, children and newborn infants) and secondly, we measured 1- and 24-hydroxylase activity in the kidney mitochrondria of rats at different ages. The mean serum levels of 1,25(OH)₂D in pregnant women, cord blood and newborns were significantly higher than those in children and non-pregnant women and adult males. In newborns, the level increased with gestational age. Synthesis of 1,25(OH)₂D was, at least in part, under the control of the fetus and newborn, rather then being solely a reflection of the conditions prevailing in the mother. The 1-hydroxylase activity in mitochondria was highest in the 1- to 2-month-old rats, and it decreased gradually thereafter. The change in 1-hydroxylase activity with age was due to a change in the V_max of the system.     

Simulated acidosis does not impair 1,25-dihydroxyvitamin D3 production by cultured kidney cells

Summary Cultured mouse kidney cells grown in serum-free medium were used to assess the metabolism of 25-hydroxyvitamin D₃ in the presence of simulated metabolic acidosis. Kidney epithelial cells isolated from 4–6 week old mice were grown to confluence in a defined serum-free medium at pH 7.4. The confluent monolayers were incubated with tritiated 25-hydroxyvitamin D₃ for 6 hours, the samples were extracted, and vitamin D metabolites were separated and quantitated by high pressure liquid chromatography (HPLC). The pH of the incubation medium was set at 6.9, 7.1, 7.4, or 7.7 by adjusting the bicarbonate concentration, using chloride as the balancing anion at constant Pco₂. When pH was altered at the beginning of the 6 hour assay, production of 1,25-dihydroxyvitamin D₃ was the same at each pH. More prolonged pH perturbation for a total of 30 hours likewise had no influence on 1,25-dihydroxyvitamin D₃ production. These results confirm that intact mammalian kidney cells in serum-free culture possess an active 25-hydroxyvitamin D₃-1-hydroxylase and that the activity of the enzyme is unaffected by pH over the range 6.8–7.7. In experiments where acidosis has been shown to alter 1,25-dihydroxyvitamin D₃ production, the mechanism was probably indirect.     

Biochemical characterization of 1,25(OH)2D3 receptors in chick embryonal duodenal cytosol

Summary This study presents measurements of serum vitamin D metabolites, calcium and phosphorus as well as measurements of the equilibrium dissociation constant for duodenal 1,25(OH)₂D₃ receptor in 15-, 18-, 19-, and 20-day chick embryos in comparison to that in 1- and 118-day-old chicks and to vitamin D-deficient chicks. The present results showed that: (a) serum 1,25(OH)₂D and 24,25(OH)₂D levels rise from 15 and 18 to days 19 and 20 of embryonic development while serum phosphate levels are stable; (b) serum calcium levels rise at hatching to adult levels; (c) the duodenal 1,25(OH)₂D₃ receptor is detectable in 15-day-old embryo and has a Kd similar to that of 118-day-old vitamin D-replete chicks; and (d) the activity of 1,25(OH)₂D₃ receptor in chick duodenal cytosol is maximal at hatching.     

Metabolic effects of thiazide and 1,25-(OH)2 vitamin D in postmenopausal osteoporosis

It was previously shown that the stimulation of intestinal calcium absorption by exogenous 25-hydroxyvitamin D (25-OHD) in postmenopausal women with osteoporosis was attenuated when thiazide was added, probably due to the suppression of endogenous synthesis of 1,25-(OH)₂ vitamin D (1,25-(OH)₂D). To test whether the above attenuation could be averted if exogenous 1,25-(OH)₂D replaced 25-OHD, 10 women with postmenopausal osteoporosis participated in a three-phase study comprising control (pretreatment), treatment with 1,25-(OH)₂D 0.5 µg/day for 4 weeks, and combined 1,25-(OH)₂D and trichlormethiazide (TZ) 2 mg/day for 4 weeks. The 1,25-(OH)₂D treatment significantly increased serum 1,25-(OH)₂D from 60±7.2 (SD) to 154±48 pmol/1, fractional intestinal calcium absorption () from 0.386 ±0.055 to 0.613±0.081, and urinary calcium from 3.7±0.8 to 6.6±1.9 mmol/day. Addition of TZ significantly reduced urinary calcium from 6.6±1.9 to 4.8±1.3 mmol/day, without changing (0.613±0.081 to 0.584±0.070), serum calcium or 1,25-(OH)₂D (154±48 to 154±38 pmol/1). Thus, estimated calcium balance (absorbed minus urinary calcium, increased marginally to +5.6 mmol/day on 1,25-(OH)₂D alone (p=0.028) and significantly to +6.8 mmol/day on 1,25-(OH)₂D+TZ, from the control value of +4.0 mmol/day. Seven patients who were treated long-term with combined 1,25-(OH)₂D and TZ for 11–29 months maintained their a (0.593±0.099) and a marginally more positive estimated calcium balance (+6.4 mmol/day,p=0.025 from the control phase). Moreover, there was a stability of bone density of radial shaft, femoral neck, and lumbar spine. In conclusion, when exogenous 1,25-(OH)₂D is provided, TZ does not lower serum 1,25-(OH)₂D and in patients with postmenopausal osteoporosis. Thus, the hypocalciuric action of TZ may lead to improved calcium balance and may potentially attenuate further bone loss.     

Induction of macrophagic and granulocytic differentiation of murine bone marrow progenitor cells by 1,25-dihydroxyvitamin D3

Summary 1,25-Dihydroxyvitamin D₃ (1,25(OH)₂D₃) was recently shown to promote maturation of 5-fluorouracil (5FU)-treated bone marrow cells by up-regulating macrophage-colony stimulating factor (M-CSF) receptors in the presence of interleukin la (IL-1). In order to reveal how 1,25(OH)₂D₃ interacts with colony-stimulating factors and regulates the differentiation of bone marrow progenitor cell populations, in the present study, natural bone marrow cells were isolated from untreated mice and used in a-minimum essential medium supplemented with 20% heat-inactivated horse serum without added appropriate cytokines. Under the conditions, cells spontaneously differentiated gradually with days of culture, as assessed by expression of macrophage differentiation antigens such as Mac-1 (CD11b) and F4/80. Both M-CSF and granulocyte macrophage-colony stimulating factor (GM-CSF) induced only Mac-1 antigen expression. Simultaneous treatment with M-CSF and 1,25(OH)₂D₃ enhanced the M-CSF's effect on expression of both antigens, although (1,25(OH)₂D₃) per se has no effect on the expression for up to 11 days. In addition, successive treatment with 1,25(OH)₂D₃ and M-CSF or GM-CSF dramatically enhanced expression of both antigens or Mac-1 antigen, respectively. Similarly, both simultaneous and successive treatment with 1,25(OH)₂D₃ and M-CSF significantly enhanced phagocytic activity and H₂O₂ production, whereas successive treatment with (1,25(OH)₂D₃) and GM-CSF significantly enhanced only phagocytic activity. Enzymehistochemical study demonstrated that cells treated simultaneously or successively with 1,25(OH)₂D₃ and M-CSF were strongly positive for nonspecific esterase (NSE), a macrophage-specific marker, and that simultaneous or successive treatment with 1,25(OH)₂D₃ and GM-CSF yielded cells strongly positive for NSE or for chloroacetate esterase (ChAE), a granulocyte-specific marker, respectively. These findings suggest that 1,25(OH)₂D₃ primes bone marrow progenitor cell populations not only to M-CSF but also to GM-CSF and thereby accelerates the CSFs-dependent differentiation of the cells to the macrophage or granulocyte.     

1,25-dihydroxyvitamin D3 causes an increase in the number of osteoclastlike cells in cat bone marrow cultures

Summary The direct effect of 1,25(OH)₂D₃ upon osteoclast formation from precursor cells is still unknown. In the present experiments we have tested the effects of 1,25(OH)₂D₃ on the generation of osteoclastlike cells in cat bone marrow cultures. These cultures contain proliferating nonattached mononuclear cells and precursor cells that subsequently attach to the culture flask surface and then fuse to form multinucleated osteoclastlike cells. After 7 days of culture we separated the nonattached precursor cells from the attached cells and studied the effects of 1,25(OH)₂D₃ (10⁻¹⁰ M–10⁻⁸ M) on multinucleated cell formation in these two cell populations. In cultures derived from the non-attached precursor cells, 7 days of treatment with 1,25(OH)₂D₃ (10⁻⁸ M) resulted in a 180% increase in the number of attached mononuclear cells and a 90% increase in the number of nuclei contained within multinucleated cells. These effects were dose-dependent. 1,25(OH)₂D₃ did not have a consistent effect on the number of nonattached precursor cells. In cultures derived from attached cells, 7 days of treatment with 1,25(OH)₂D₃ (10⁻⁸ M) induced a 50% increase in the number of mononuclear attached cells and a 40% increase in the number of nuclei within polykaryons. The most likely explanation for these results is that 1,25(OH)₂D₃ promotes the differentiation and subsequent adhesion of nonattached precursor cells, stimulates proliferation of attached mononuclear precursor cells, and possibly stimulates fusion of these attached precursor cells.     

Idiopathic juvenile osteoporosis: Evidence of normal osteoblast function by 1,25-dihydroxyvitamin D3 stimulation test

Summary Idiopathic juvenile osteoporosis (IJO) is a rare form of bone demineralization that occurs during childhood. The mechanism of bone loss is unclear. Some bone hystomorphometric studies have found osteoblast failure and decreased bone formation in the affected patients whereas others have reported increased bone resorption. To elucidate this issue, we studied osteoblast function in six patients with IJO (five males, one female; aged 2.3–14.6 years) and five healthy sex- and age-matched subjects (four males, one female; aged 2.0–15.1 years) measuring serum values of osteocalcin under basal condition and during an osteoblast stimulation test performed by oral 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] administration (1.8 g/1.73 m²/daily). After a baseline day (day 0), all the subjects (patients and controls) received 1,25(OH)₂D₃ in four divided doses for 6 days (days 1–6). Fasting blood samples were obtained every morning (0800 h) for the determination of serum osteocalcin. Baseline osteocalcin levels were not significantly different between IJO and controls (13.58±6.05 ng/ml versus 16.04±5.09 ng/ml, respectively) even if two patients had low osteocalcin values. During 1,25(OH)₂D₃ administration, serum osteocalcin values significantly increased (P<0.001) from baseline in both children with IJO and controls, reaching peak values not significantly different in the two groups. Our results do not support the hypothesis that defective osteoblast function is the primary factor of bone demineralization in IJO.     

Serum calcium regulating hormones in the perinatal period

Summary To clarify perinatal vitamin D metabolism, we measured 25-hydroxyvitamin D (25OHD), 24,25-dihydroxyvitamin D [24,25(OH)₂D], 1,25-dihydroxyvitamin D [1,25(OH)₂D], calcium (Ca), phosphorus (P), parathyroid hormone (PTH), and human calcitonin (CT) in paired maternal, cord, and infant serum. Cord serum 25OHD was significantly lower than the maternal level, and cord serum 24,25(OH)₂D was also significantly below the maternal concentrations. Maternal, cord, and infant serum 1,25(OH)₂D, on the other hand, was significantly higher than the normal adult level. The serum PTH was low, but the CT concentration was high in the cord. Cord serum Ca and P levels were significantly higher than maternal. The reason for the elevated circulating 1,25(OH)₂D level in the perinatal period is uncertain, and we speculate that the possible factors are gonadal steroids, placental lactogen, prolactin, and CT. In addition, serum 24,25(OH)₂D and 1,25(OH)₂D concentrations are under some control by the fetus.     

Coordinate inhibition of alkaline phosphatase and type X collagen syntheses by 1,25-dihydroxyvitamin D3 in primary cultured hypertrophic chondrocytes

Summary The effects of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) (2.3×10^-12-1.4×10^-6 [M]) on alkaline phosphatase, collagen, and cell proliferation were examined in primary cultured hypertrophic chondrocytes prepared from the distal epiphyseal growth plate of the tibias of 12-day chick embryos. 1,25(OH)₂D₃ showed time- and dose-dependent inhibitory effects on the alkaline phosphatase and collagen levels. The inhibition of alkaline phosphatase activity became detectable at 2×10^-11 [M] and reached 10% of control at 10^-7 [M]. The concentration of 1,25(OH)₂D₃ giving a 50% inhibition of the enzyme level was approximately 3×10^-10 [M]. Of the two extracellular collagen pools, a cell-associated matrix pool showed a more dramatic decrease (to 10% of control) than a culture medium pool (to 50% of control) at increased 1,25(OH)₂D₃ concentrations. The degree of inhibition was different for each type of chondrocyte-specific collagen (types II, IX, X, and XI). Types II and IX were inhibited in a parallel manner to only 60–80% of control. On the other hand, types X and XI were more greatly reduced up to 10% of control, and their dose-dependent inhibitory curves were similar to that of alkaline phosphatase. On cell proliferation, 1,25(OH)₂D₃ had a biphasic effect: stimulation at 10^-10–10^-8 [M] and inhibition at higher levels. The results revealed the significant involvement of 1,25(OH)₂D₃ in the metabolism of two probable calcification-related products, alkaline phosphatase and type X collagen.     

Alkaline phosphatase inhibition by levamisole prevents 1,25-dihydroxyvitamin D3-stimulated bone mineralization in the mouse

Summary To determine the relationship between alkaline phosphatase (AP), 1,25(OD)₂D₃ and bone formationin vivo, we have examined the effects of levamisole, a stereospecific inhibitor of AP on bone formation and on 1,25(OH)₂D₃-stimulated bone mineralization in the mouse. Normal mice were injected daily with levamisole at doses of 40 and 80 mg/kg/b.w. The compound was given alone or in combination with 1,25(OH)₂D₃ infusion (0.05 μg/kg/d) for 7 days. Treatment with levamisole alone inhibited the serum AP activity (mainly of skeletal origin in mice) by 18.4 and 61.3% for the low and high dose respectively. No deleterious effect on body growth, tibia length, and bone cells population was detected. The moderate inhibition of AP activity produced by the lower dose of levamisole alone (18.4%) or in combination with 1,25(OH)₂D₃ (37.9%) was associated with a reduced endosteal matrix apposition rate (MaAR) determined by double³H-proline labeling method. This effect was related to a levamisole-induced fall in serum phosphate. Despite the moderate inhibition of AP activity, the mineral apposition rate (MiAR) determined by the double tetracycline labeling method remained normal. Moreover, 1,25(OH)₂D₃ infusion still resulted in increased MiAR which was stimulated to the same extent as in the absence of levamisole. By contrast, the more severe inhibition of AP activity induced by 80 mg/kg of levamisole alone (61.3%) or in combination with 1,25(OH)₂D₃ (45.8%) inhibited both the MaAR and the MiAR and prevented the stimulatory effect of 1,25(OH)₂D₃ on bone mineralization. The data show that AP activity affects the bone matrix and mineral apposition ratesin vivo and that severe inhibition of AP activity inhibits the 1,25(OH)₂D₃-induced stimulation of bone mineralization in the mouse.     

Influence of 1,25-dihydroxyvitamin D3 on cell proliferation during odontogenesis of the mouse embryonic molarsIn vitro

Summary Mandibular first molars from 17-day-old mouse embryos were cultured for 2 and 4 days in alpha-MEM supplemented with 10% newborn bovine serum containing 0.02% ethanol or 0.1, 1.0 or 10 ng/ml 1,25-(OH)₂D₃. After embedding, every 6th section was stained and mitotic features of inner dental epithelium (IDE) and dental papilla cells (DP) were counted under a light microscope. On the 2nd day, no significant differences were observed in the IDE and DP mitotic indexes among the control, ethanol, and the three vitamin D groups. On the 4th day, the indexes for all groups decreased. But the IDE indexes for all vitamin D groups were significantly different from those for the control (P<0.01) and ethanol (P<0.05) groups, whereas the DP index was significant (P<0.05) only in the 10 ng/ml vitamin D group. The present results suggest that vitamin D₃ may have an influence on cell proliferation of IDE and DP in mouse embryonic molarsin vitro.     

Evidence that factors other than 1,25 dihydroxyvitamin D may play a role in augmenting intestinal calcium absorption in patients with primary hyperparathyroidism

Summary We examined 17 patients with primary hyperparathyroidism for their serum 1,25 dihydroxyvitamin D levels and for their fractional intestinal calcium absorption rates using a whole body counter and calcium-47. As controls, 10 normal volunteers were examined both before and after administration of 1α-hydroxyvitamin D to increase serum 1,25 dihydroxyvitamin D. Values of serum 1,25 dihydroxyvitamin D were 71.6±37.6 pg/ml (mean ±SD) in patients with primary hyperparathyroidism and 75.3±27.7 pg/ml (mean ±SD) in normal volunteers after administration of 1α-hydroxyvitamin D, while values of intestinal calcium absorption rate were 61.5±16.5% (mean ±SD) in patients with primary hyperparathyroidism and 34.1±5.1% (mean ±SD) in normal controls, respectively. There was a positive correlation between values of serum 1,25 dihydroxyvitamin D and intestinal calcium absorption in both groups. However, in patients with primary hyperparathyroidism, intestinal calcium absorption was more increased than that in normal volunteers when compared to their serum values of 1,25 dihydroxyvitamin D. This suggests that another factor than 1,25 dihydroxyvitamin D plays an important role in the intestinal calcium absorption in patients with primary hyperparathyroidism.