Effects of 1 alpha-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, 1,24,25-trihydroxyvitamin D3, and 1,25,26-trihydroxyvitamin D3 on mineral metabolism and 1,25-dihydroxyvitamin D concentrations in dairy cows

Six mature, nonlactating, nonpregnant Jersey cows were treated with five 1-alpha-hydroxylated metabolites of vitamin D3 to compare relative potencies of the metabolites. Blood plasma 1,25-dihydroxyvitamin D peaked at about 1000 pg/ml 12 h after intramuscular injection of 500 micrograms 1,25-dihydroxyvitamin D3 but returned to preinjection concentration within 3 to 4 days. Administration of 500 micrograms 1-alpha-hydroxyvitamin D3 intramuscularly led to a gradual increase in 1,25-dihydroxyvitamin D concentration to 500 pg/ml 48 h after treatment. When 500 micrograms of 1,25-dihydroxyvitamin D3 or 1 alpha-hydroxyvitamin D3 were given orally, plasma 1,25-dihydroxyvitamin D peaked at about 200 and 100 pg/ml, respectively. The decline from peak concentrations occurred more slowly after oral treatment than after intramuscular treatment. Plasma calcium was increased by 20 to 30% for a week or more, depending on 1,25-dihydroxyvitamin D concentrations in plasma. All treatments resulted in calciuria. Treatment with 1 or 3 mg doses of 1,24(R),25-trihydroxyvitamin D3 or both carbon-25 stereoisomers of 1,25,26-trihydroxyvitamin D3 induced smaller and less protracted changes in plasma minerals.

Elevated plasma cortisol during induced and spontaneous hypocalcemia in ruminants

The relationship of cortisol in blood plasma with plasma calcium and phosphorus was studied from 3 days before to 2.5 days after calving in 12 dairy cows (third or more parity). Cows were in three groups: 1) paretic (displayed hypocalcemic and lateral recumbency), 2) nonparetic (plasma calcium at least 8.0 mg/100 ml), and 3) borderline (plasma calcium less than 8.0 mg/100 ml). Cortisol concentrations from 0 to 1.5 days postpartum reflected the state of calcium stress of the groups, paretic more than borderline and borderline more than nonparetic. Phosphorus was lower from 0 to 1 day postpartum in paretic cows. Calcium and phosphorus were negatively correlated (within cow) with cortisol (-.53, -.37). In experiments with goats, cortisol was released in response to hypocalcemia and displayed no activity in initiating an onset of hypocalcemia when given exogenously. Also, the observation that cortisol-treated goats responded less severely with calcium depression and recovered faster from induced hypocalcemia by ethylene glycol-bis (beta-amino-ethyl ester) N,N'-tetraacetic acid infusions suggests cortisol may aid the animal in recovering from hypocalcemia.

Comparative effects of some hydroxylated vitamin D metabolites on parathyrin secretion by dispersed rat parathyroid cells in vitro

We have previously discussed the action of 1 alpha,25-(OH)2D3, (24R) 24,25-(OH)2 D3 and (25S) 25,26-(OH)2D3 on parathyrin secretion by isolated rat parathyroid cells. In this work, we have compared these effects with those obtained with 1 alpha-OH D3, 25-OH D3 and 1 alpha-OH D2. In decreasing order, the activities were: 1 alpha,25-(OH)2D3 greater than 1 alpha-OH D3 greater than (24R) 24,25-(OH)2D3 greater than 25-OH D3 greater than (25S) 25,26(OH)2D3 greater than 1 alpha-OH D2. The presence of two hydroxyl groups with one hydroxyl group in alpha position seems to have the higher activity to inhibit the parathyroid secretion. At least, the nature of the side chain conformation also plays a part upon the effect of PTH release.

Effect of cholecalciferol derivatives on the mechanical properties of chick bones

Chicks were depleted of vitamin D, divided into groups, and treated daily with (a) cholecalciferol, (b) 1 alpha-hydroxycholecalciferol [1 alpha (OH)-D3], (c) 24R, 25-dihydroxycholecalciferol [24R,25-(OH)2D3], or (d) 1 alpha (OH)D3 and 24R,25(OH)2D3. Two additional groups of chicks were studied, one that was continuously depleted of vitamin D, and another that was continuously supplemented with the vitamin, since day 1. After killing, the tibiae were removed and tested for their mechanical properties. Bending load was applied to the midshaft, and the intrinsic properties of this site, its quantity and geometry were analyzed. From a mechanical point of view, the weakest bones found were of birds depleted of vitamin D, whereas the strongest were of those treated with 1 alpha (OH)D3. Only the bones of the 24R,25(OH)2D3-treated or the 1 alpha (OH)D3 and 24R,25(OH)2D3-treated groups of birds showed mechanical properties comparable to those obtained with vitamin D-replete chicks.

23S,25-dihydroxyvitamin D3 as a circulating metabolite of vitamin D3. Its role in 25-hydroxyvitamin D3-26,23-lactone biosynthesis

23,25-Dihydroxyvitamin D3 was isolated from vitamin D-toxic pig plasma by sequential chromatography through two gravity columns and three high performance liquid chromatography systems. Two of the high performance liquid chromatography systems separated the R and S diastereomers of 23,25-dihydroxyvitamin D3 and demonstrated that the metabolite has the 23S configuration. Ultraviolet absorbance and mass spectroscopy of the pure metabolite and mass spectroscopy of its trisilylated derivative confirmed the structural assignment. 23S,25-Dihydroxyvitamin D3, 23R,25-dihydroxyvitamin D3, 25S,26-dihydroxyvitamin D3, and 25R,26-dihydroxyvitamin D3 were assessed for their ability to produce 25-hydroxyvitamin D3-26,23-lactone in vitamin D2-toxic rats. On 23S,25-dihydroxyvitamin D3, of the naturally occurring compounds, was able to increase the plasma lactone concentration. This metabolite was a more efficient precursor than 25-hydroxyvitamin D3, suggesting that 23S-hydroxylation is a rate-limiting step in 25-hydroxyvitamin D3-26,23-lactone formation. 23S,25-Dihydroxyvitamin D3 was not detected in 25-hydroxyvitamin D3-dosed rats, indicating that the former is rapidly metabolized. Nephrectomized rats had a diminished but significant ability to synthesize 25-hydroxyvitamin D3-26,23-lactone from 25-hydroxyvitamin D3. Nephrectomy did not affect synthesis of 25-hydroxyvitamin D3-26,23-lactone from 23S,25-dihydroxyvitamin D3. These results demonstrate that vitamin D3 23S-hydroxylase(s) are also located extrarenally and that extrarenal tissues are quantitatively important to 25-hydroxyvitamin D3-26,23-lactone synthesis.

24-hydroxylation of 25-hydroxyvitamin D3: is it required for embryonic development in chicks?

As shown previously, laying hens given 1,25-dihydroxyvitamin D3 as their sole source of vitamin D produce fertile eggs having normal shells, but only 35 to 55 percent of the embryos are normal. Giving these hens additional 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or 24,24-difluoro-25-hydroxyvitamin D3 at 1.25 nanomoles per day resulted in 90 to 100 percent normal embryos, and hence, hatchability. Since 24,24-difluoro-25-hydroxyvitamin D3 cannot be 24-hydroxylated, 24-hydroxylation is not required for this function of 25-hydroxyvitamin D3.

Chemical synthesis, biological activity, and metabolism of 25-hydroxy-24-oxovitamin D3

25-Hydroxy-24-oxovitamin D3 (25(OH)24-oxo-D3), a metabolite of 25-hydroxyvitamin D3, has been chemically synthesized. The ultraviolet, mass, infrared, and proton nuclear magnetic resonance spectra of the 25(OH)24-oxo-D3 were identical with those of the natural product isolated from chick kidney incubates. The oxo compound showed biological activity similar to 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) in vitamin D-deficient chicks in enhancing intestinal calcium transport and bone calcium mobilization activities. Although 25(OH)24-oxo-D3 partially restored the impaired eggshell weights of Japanese quails fed a vitamin D-deficient diet, it was much less potent than 25-hydroxyvitamin D3 or 1 alpha, 25-dihydroxyvitamin D3. In addition, there was no effect on the calcification of medullary bone. When 25(OH)24-oxo[3H]D3 was incubated with kidney homogenates from vitamin D-deficient chicks, it was metabolized to [3H]1 alpha, 24,25-trihydroxyvitamin D3 and a metabolite which was eluted in a region between authentic 24R,25(OH)2D3 and 1 alpha, 25-dihydroxyvitamin D3 on high pressure liquid chromatography. In the incubates of kidney homogenates from vitamin D-supplemented chicks, those metabolites were not detected. In vitamin D-supplemented chicks, the recovery of radioactivity in the chloroform phase extracted by the method of Bligh and Dyer was only 50%, while that in vitamin D-deficient chicks was 87%. Moreover, the radioactivity eluted in the 25(OH)24-oxo-D3 fraction from vitamin D-supplemented chicks was only one-fifth of that from vitamin D-deficient birds. The present results indicate that the 24-oxidation of 24,25(OH)2D3 may be a route of inactivation of vitamin D3.

Factors affecting the calcium, magnesium and phosphorus content of beef cow milk

This paper reports the calcium, magnesium and phosphorus content of milk from Shorthorn cattle during the five month calf nursing period as well as the effect of prepartum administration of a single intramuscular dose of vitamin D3 or of 25-hydroxyvitamin D3 on the milk mineral constituents. The colostrum of the group which received 25-hydroxyvitamin D3 was found to contain a higher percentage of calcium on the second and third day than the colostrum of control cows or those receiving D3. No differences occurred in colostrum magnesium or phosphorus contents due to prepartum treatment. Calcium, magnesium and phosphorus concentrations were all high in the first day of lactation, but declined until the third day after parturition. Milk calcium, magnesium and phosphorus content of individual cows was not uniform throughout the lactation and the variation was different for different cows.

Inhibition of the in vitro growth of Plasmodium falciparum by D vitamins and vitamin D-3 derivatives

D vitamins are effective inhibitors of the in vitro intraerythrocytic growth of Plasmodium falciparum. Disappearance of the parasitemia was observed after 48 h contact between infected cells and 5 x 10(-6) M 1 alpha-hydroxycholecalciferol, 5 x 10(-5) M 25-hydroxycholecalciferol (25-OH-D-3), 1 alpha, 25-dihydroxycholecalciferol or 2.5 x 10(-4) vitamin D-2 and D-3. A 48 h pretreatment of healthy erythrocytes with 5 x 10(-5) M 25-OH-D-3 did not change their susceptibility to invasion by the parasite and their ability to support the growth of P. falciparum. Ionomycin, a calcium ionophore, and EGTA prevented parasite development at concentrations greater than 2 x 10(-7) M and 4 x 10(-4) M, respectively, but did not antagonize the inhibitory activity of 25-OH-D-3. Addition of 25-OH-D-3 for 12 or 24 h duration to synchronized cultures, showed that the drug had a schizonticidal action, but was without effect when parasites were in the ring form.

New bone formation and parathyroid activity effected by 1 alpha-hydroxyvitamin D3

Adult male rats reared on a standard diet were treated with peroral dosages of 1 alpha-hydroxyvitamin D3 (1 alpha-OHD3). A rapid effect on the serum calcium level was found; the elevation (compared to untreated controls) occurred as early as two weeks and remained elevated throughout the treatment period. Histomorphometric analysis revealed a decreased resorption rate and increased incorporation of tetracycline after four weeks of 1 alpha-OHD3 treatment. These results were associated with a significant increase of cortical as well as trabecular bone, as well as increased levels of bone hydroxyproline and hexosamines. A clearly significant decrease in the total volume of parathyroids was found after six weeks; this was accompanied by a slight pycnosis of the chief cells, which may account for reduced parathyroid activity.

Comparison of acute effects of 1.25- and 24.25-dihydroxy-vitamin D3 in normal subjects

Effects of small iv doses of 1.25-dihydroxy- and 24.25-dihydroxy-vitamin D3 (a microgram) were studied in 10 normal subjects. Injection of 1.25 (OH)2D3 was associated with small but significant increases in plasma calcium and phosphate but plasma levels of immunoreactive parathyroid hormone (iPTH) and calcitonin (iCT) did not change. The administration of 24.25 (OH)2D3 was associated with comparable decreases in plasma calcium and a small and transient decrease in plasma iPTH. Plasma levels of iCT did not change. 24.25 (OH)2D3 also significantly increased glomerular filtration rate and decreased the urinary excretion of noradrenaline, in contrast to 1.25 (OH)2D3 which had no effect on these variables. The rapid infusion of calcium significantly decreased levels of iPTH. We conclude that small doses of 1.25 (OH)2D3 and 24.25 (OH)2D3 have little, if any, direct effect on the secretion of PTH and CT in man.

Effect on serum calcium of a alpha-hydroxy-vitamin D3 supplementation in infants of low birth weight, infants with perinatal asphyxia, and infants of diabetic mothers

Thirty infants of low birth weight, 35 infants with perinatal asphyxia, and 16 infants of diabetic mothers were investigated for early neonatal hypocalcaemia. The infants were randomized into a group prophylactically given 1 alpha-hydroxy-vitamin D3, 0.05 or 0.10 micrograms/kg i.v. on the first 3 days of life, and an untreated control group. In infants of low birth weight and infants of diabetic mothers there were no differences in serum ion-Ca concentrations on days 2, 3, 5, and 7 between the treated and untreated groups. In infants with perinatal asphyxia, however, serum ion-Ca concentrations on days 5 and 7 were significantly higher in the treated than in the untreated group, while on days 2 and 3 the differences were not statistically significant. The hypocalcaemia in asphyctic infants was not correlated to bicarbonate treatment, but infants with severe signs of asphyxia had lower serum ion-Ca concentrations than infants with only mild or no signs. Hypocalcaemia in asphyctic infants might be explained by a decreased concentration of 1 alpha, 25-dihydroxy-vitamin D3 following reduced 1 alpha-hydroxylation in the kidney as a consequence of anoxia during perinatal asphyxia.

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

Two groups of adult male rats were treated perorally for 6 weeks with 0.1 microgram and 1.0 microgram of 1a-hydroxyvitamin D3 (1a-OH-D3), respectively. The effect of the treatment on cancellous bone matrix was studied by chemical analysis and morphometric measurements. The effect of the 1.0 microgram dose on the inorganic composition, and on the calcification of the cancellous bone matrix, was significantly more pronounced, decreasing the amount of glycosaminoglycans. The lower dose level, 0.1 microgram of 1a-OH-D3, increased the collagen metabolism, whereas the higher dose level did not. The amount of cancellous bone determined morphometrically increased significantly during treatment with both dose levels. 1a-OH-D3, converted in the organism to the hormonal form 1.25 (OH)2D3, induces new bone formation, probably by direct influence on the cancellous bone tissue itself.

Evidence for acute inhibitory effects in vivo of 1 alpha-hydroxycholecalciferol on parathyroid hormone secretion in rats

In an attempt to elucidate the influence of 1 alpha-hydroxycholecalciferol (1 alpha OHD3) on parathyroid hormone (PTH) secretion, sequential measurements were made of 1) serum calcium and urinary excretion of cAMP in conscious perfused rats, and 2) serum calcium in nephrectomized rats; also, the effects of a single iv injection of 1 alpha OHD3 on these parameters were examined. In conscious perfused rats, 6.25 micrograms/kg (15 nmol/kg) 1 alpha OHD3 reduced the urinary excretion of cAMP (approximately 40% of the initial value; P less than 0.05), which reached a level compatible with that of parathyroidectomized rats at 4 h; this fall was sustained for 24 h. Serum concentrations of calcium (total and ionized) did not change at 6 h, and increased at 24 h. In parathyroidectomized rats which were continuously infused with bovine PTH (0.75 U/h), the vitamin D preparation had no significant effect on the urinary excretion of cAMP. Nephrectomy, followed by an injection of the vehicle (0.05 ml 99.5% ethanol), induced a transient hypercalcemia (13.12 +/- 0.39 mg/dl at 6 h). This hypercalcemic response was prevented by prior parathyroidectomy. Injections of 1.25 and 6.25 micrograms/kg 1 alpha OHD3 caused a significant suppression of the hypercalcemia (P less than 0.05 and P less than 0.1, respectively) in the presence of parathyroid glands, whereas a dose-related hypercalcemic effect was observed in their absence. These results suggest that in rats, 1 alpha OHD3, either directly or most probably after conversion into 1 alpha, 25-dihydroxycholecalciferol, 1) acutely inhibits PTH secretion without causing a significant rise in serum calcium, and 2) suppresses PTH secretion in secondary hyperparathyroidism induced by nephrectomy.

Influence of 25-hydroxyvitamin D3 on thyrotropin and triiodothyronine plasma levels in man

The influence of three-day oral administration of 100 microgram 25-hydroxycholecalciferol (25-HCC) on thyrotropin (TSH), triiodothyronine (T3), calcium and phosphorus plasma levels was investigated along with changes of Qet and Qat intervals on the electrocardiographic tracing. It was found that 25-HCC in an acute trial significantly elevates the TSH level and causes a slight decline of the T3 level. Changes in the calcium and phosphorus levels were not significant. No changes of the electrocardiographic tracing were found. The results suggest that 25-HCC interferes with the process of secretion (or metabolization) of TSH (and perhaps also T3), probably via changes of the calcium ion concentration in cytosol of secretory cells.

Formation of osteoclasts from blood monocytes during 1 alpha-OH Vit D-stimulated bone resorption in mice

In order to investigate a monocyte origin for osteoclasts, tritiated thymidine labelled blood monocytes, harvested from the blood of donor mice, were injected intravenously into syngeneic recipient animals in which osteoclast formation was being stimulated by concomitant intraperitoneal injections of 1 alpha-hydroxycholecalciferol. Labelled osteoclasts were found in autoradiographs prepared from the femurs of recipient mice, demonstrating for the first time that, during hormonally stimulated osteoclast formation, blood monocytes form one source of osteoclasts.

Effect of 25-hydroxyvitamin D3 on vitamin D metabolites in primary biliary cirrhosis

The osteopenic bone disease associated with primary biliary cirrhosis is thought to be de to a deficiency in vitamin D or its metabolites. However, this has never been proven. Therefore, we measured serum levels of 25-hydroxyvitamin D3 (25-OHD3), 1,25-dihydroxyvitamin D (1,25(OD)2D), and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3), before and after a 1 yr treatment with oral 25,OHD3, in 10 patients with primary biliary cirrhosis selected because of documented osteopenic bone disease. Only in 1 patient was the pretreatment serum 25-OHD3 level below normal, less than 4.4 ng/ml. In 8 patients the serum 25,OHD3 level was in the low normal range and in one, was above normal. Serum levels of 1,25(OH)2D, the vitamin D metabolite with the greatest stimulatory effect on intestinal calcium absorption, were normal in 9 patients and elevated in 1. In contrast, serum levels of 24,25-(OH)2D3, a metabolite whose function is not known with certainty, were undetectable in 8 patients, low normal in a ninth, and normal in 1 patient who had been on large amounts of vitamin D2 (50,000 U b.i.w.,) before the start of the study. After 1 yr of treatment with oral 25-OHD3, serum 25-OHD3 rose to above normal in 9 patients. Serum 1,25-(OH)2D levels did not change significantly, while 24,25-(OH)2D3 rose to normal levels or higher in 9 of 10 patients. The bone disease of primary biliary cirrhosis is not due to 25-hydroxyvitamin D deficiency alone and is certainly not due to a deficiency of 1,25-(OH)2D as has been postulated. It may be related to low blood levels of 24,25-(OH)2D3 or to other as yet undefined factors.

Immunological effects of 1alpha-hydroxycholecalciferol (1alpha-OH-D3) and its metabolites

An immunosuppressive substance was detected in the serum and plasma of hemodialysis patients. There was a marked increase in its activity immediately after hemodialysis. This substance was not detected in the plasma of hemodialysis patients treated with 1alpha-hydroxycholecalciferol (1alpha-OH-D3), although its disappearance was unrelated to either the total dose or the duration of treatment with 1alpha-OH-D3. During in vitro studies, 1alpha-OH-D3 did not change the phytohemagglutinin-, staphage lysate- and concanavalin A-induced and spontaneous lymphoproliferation of peripheral blood lymphocytes (PBL) from a healthy person. Furthermore, addition of 1alpha-OH-D3 to the plasma of hemodialysis patients who had not received 1alpha-OH-D3 did not interfere with the suppressive activity. On the other hand, 1alpha,24(R)-dihydroxycholecalciferol, 1alpha,24(S)-dihydroxycholecalciferol, and 1alpha,25-dihydroxycholecalciferol, which are all metabolites of 1alpha-OH-D3, suppressed mitogen-induced lymphoproliferation of PBL from a healthy person.

Suppressive effects of 24,25-dihydroxycholecalciferol on bone resorption induced by acute bilateral nephrectomy in rats

The possible suppressive effects of 24,25-dihydroxycholecalciferol on secondary hyperparathyroidism and increased bone resorption were investigated in adult rats raised on a diet normal in calcium, phosphorus, and vitamin D, and subjected to acute bilateral nephrectomy. The animals had received subcutaneous radiocalcium 4 wk before the experiment. 5 h after nephrectomy an increase in serum total calcium, (45)Ca-specific activity, citrate, phosphorus, and magnesium concentrations were observed. Serum immunoreactive parathyroid hormone increased, while serum calcitonin decreased. The osteoclast count in the tibial metaphyses was augmented. The biochemical and histological changes observed were partly parathyroid hormone and calcitonin independent, as they also occurred in parathyroidectomized hypocalcemic rats. Pretreatment with 650 pmol of 24,25-dihydroxycholecalciferol 16 h before nephrectomy prevented bone calcium mobilization and diminished the rise in serum total calcium and citrate both in parathyroid-intact and in parathyroidectomized animals. In parathyroid-intact rats, serum immunoreactive parathyroid hormone and calcitonin remained normal in spite of the fall in serum-ionized calcium, and the number of osteoclasts did not increase. In parathyroidectomized rats, 24,25-dihydroxycholecalciferol did not prevent the postnephrectomy rise in the osteoclast count. This latter observation suggests that this metabolite exerts its effect on bone either by acting on cells other than osteoclasts, i.e., the osteocytes, or by inhibiting cell activity. At equimolar dosage 1,25-dihydroxycholecalciferol had a potent stimulatory effect on bone resorption. This effect of 1,25-dihydroxycholecalciferol was partly blocked by the simultaneous administration of 24,25-dihydroxycholecalciferol. The potential clinical significance of these observations remains to be determined.

Tubular handling of Pi: localization of effects of 1,25(OH)2D3 and dietary Pi in TPTX rats

Previous clearance studies have shown that chronic administration (26 pmol/day i.p. for 7 days) of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) decreases the tubular reabsorptive capacity for inorganic phosphate (Pi) in thyroparathyroidectomized (TPTX) rats. In the present study the tubular localization of this effect was examined by free-flow micropuncture in TPTX rats. At the mentioned dosage, 1,25(OH)2D3 inhibited net Pi reabsorption in the early portion of the proximal tubule. In addition, 1,25(OH)2D3 treatment altered the difference in Pi delivery between the distal tubule and the final urine, suggesting an inhibition of net Pi reabsorption along the terminal portion of the nephron, or, alternatively, admixture of tubular fluid with higher Pi concentration from deep nephrons. Finally, in TPTX rats the tubular localization of the effect of varying the dietary Pi content was found to be quite similar to that of 1,25(OH)2D3.

Effect of 1,25-dihydroxyvitamin D3 on phosphate homeostasis in the X-linked hypophosphatemic (Hyp) mouse

We studied the effect of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on homeostasis of inorganic phosphate (Pi) in murine hypophosphatemia (Hyp), a homologue of X-linked hypophosphatemia (XLH) in man. Normal mice given 1,25-(OH)2D3 (83 pg/g.d) by continuous subcut, infusion x 10 d) had a significant rise in plasma calcium (Ca) (p less than 0.001), plasma Pi (p less than 0.025) and fractional Ca excretion (p less than 0.001), without change in fractional Pi excretion or Na+-stimulated Pi transport in purified renal brush-border membrane vesicles (BBMV). Hyp littermates did not respond to this dose of 1,25-(OH)2D3. At 415 pg/g.d, Hyp mice had increased plasma Ca (p less than 0.001), fractional Ca excretion (p less than 0.001), and plasma Pi (p less than 0.001) but no change in either fractional Pi excretion or Na+-stimulated Pi transport in BBMV. At this dose, 1,25-(OH)2D3 also stimulated Pi transport by everted sacs of Hyp small intestine (p less than 0.001). No deficiency of Pi transport was found in untreated Hyp intestine. We conclude that 1,25-(OH)2D3 improves Pi homeostasis in the Hyp phenotype by its effect on intestine; the defect in renal Pi reabsorption remains unchanged.

Effect of lead ingestion on functions of vitamin D and its metabolites

A study of the effect of ingestion of lead on the metabolism and function of vitamin D was carried out in rats fed diets varying in calcium and phosphorus content. The ingestion of 0.82% lead as lead acetate suppressed plasma levels of 1,25-dihydroxycholecalciferol in rats fed either a low phosphorus or a low calcium diet while it had no effect on this parameter in rats fet either a high calcium diet or a normal phosphorus diet. Most important, the ingestion of lead totally blocked the intestinal calcium transport response to cholecalciferol, 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol. On the other hand, the ingestion of lead acetate had no influence on the mobilization of calcium from bone, the elevation of serum inorganic phosphorus and in the mineralization of rachitic bone in the same animals. Thus by the feeding of 0.82% lead on the intestinal responses to vitamin D and its metabolites was greatest in animals fed a low calcium or a low phosphorus diet, it was present with all diets tested.

Osteoclast formation in response to intraperitoneal injection of 1 alpha-hydroxycholecalciferol in mice

In order to assess osteoclast formation in response to 1 alpha-hydroxycholecalciferol, osteoclast counts per cm of bone surface were performed on paraffin sections of femurs of male CBA mice killed at daily intervals up to 5 days. All animals received daily intraperitoneal injections of 1 alpha-hydroxycholecalciferol up to the time of death. Peak osteoclast formation occurred during the third day, by the end of which maximum numbers of osteoclasts were achieved (11.9 +/- 0.9 osteoclast cm-1) compared to controls (3.5 +/- 0.6 osteoclast cm-1), this increase being highly significant (p less than 0.01). Although the osteoclast population was most dense at the metaphyseal plate in both experimental and control groups, osteoclast counts in this region only doubled whereas overall osteoclast counts more than tripled. The number of nuclei per osteoclast did not significantly alter following four daily injections of 1 alpha-hydroxycholecalciferol.

1,25-Dihydroxyvitamin D3 stimulates the alkaline phosphatase activity of osteoblast-like cells

Rat osteogenic sarcoma cells which have osteoblast properties including the ability to form bone and to mineralize were recently found to possess specific cytoplasmic receptors for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). We have examined now the effect of 1,25(OH)2D3 and other vitamin D3 metabolites on the alkaline phosphatase of such cell lines. We found in two cell lines cultured in the presence of 10(-7) M 1,25(OH)2D3 a 3-fold increase in intracellular alkaline phosphatase activity and a 6-fold increase in secreted alkaline phosphatase activity. The cellular response occurred in a dose-dependent fashion at a range of 10(-9) to 10(-7) M. In a third cell line, which does not possess the specific receptor for 1,25(OH)2D3, we could not detect stimulation of alkaline phosphatase. Vitamin D3, 25-dihydroxyvitamin D3, and 24,25-dihydroxyvitamin D3 at 10(-7) M had no effect on alkaline phosphatase. The effect of 1,25(OH)2D3 was enhanced in the presence of increased calcium. In view of the postulated role for alkaline phosphatase in calcification, we speculate that the stimulatory effect of 1,25(OH)2D3 on the alkaline phosphatase activity of osteoblast-like cells indicates a direct involvement of 1,25(OH)2D3 in bone mineralization.

Impaired bone resorption of cultured calvaria from mice with abnormal lysosomal function (the Chediak-Higashi syndrome)

Spontaneous bone resorption is reduced in cultured calvarial bones from mice with the Chediak-Higashi syndrome, as indicated by decreased mobilization of calcium from the bones to the medium. Although bone resorption in calvaria from mice with this disease can be stimulated by PGE2 and 1 alpha (OH)D3, the amounts of mineral released after stimulation is also decreased.

Intestinal absorption of calcium: role of dietary phosphate and vitamin D

The intestinal absorption of calcium (Ca) has been shown to depend on vitamin D3, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], and dietary phosphorus (P) concentration. This study was designed to evaluate the role of dietary P independent of vitamin D3 or 1,25(OH)2D3. Vitamin D-deficient rats were studied during dietary P restriction and were compared with control groups raised on a normal-phosphorus diet (NP). Balance studies were sued. Net intestinal Ca absorption was significantly lower with dietary P restriction compared with the NP group. This malabsorption of Ca was corrected by the administration of either D3 for 1,25(OH)2D3, despite hypophosphatemia. Everted gut sacs showed a marked reduction in the uptake of 45Ca in the duodenum, jejunum, and ileum during dietary P restriction. We concluded that dietary P concentration plays a major role in intestinal Ca absorption in the vitamin D-deficient rats. These findings suggest an effect of the low-phosphate diet on the vitamin D-dependent, Ca-transport mechanism.

Vitamin D3 metabolite injections to thyroparathyroidectomized pregnant rats: effects on calcium-binding proteins of maternal duodenum and of fetoplacental unit

Fetomaternal relationships with respect to vitamin D metabolism were investigated in thyroparathyroidectomized (TPTX) pregnant rats, with or without treatment with different vitamin D3 metabolites. Calcium-binding protein (CaBP) in maternal duodenum was used as an index of 1,25-(OH)2D3 status of the mother. Pregnant rats were TPTX on day 12.5 and CaBP was measured on 21.5 days of gestation by RIA in maternal duodenal mucosa and in the fetoplacental unit (placenta, fetal membranes, and fetal intestine). In the duodenum of TPTX mothers, the CaBP concentration was reduced by 50%. This fall was associated with a decrease of 1,25-(OH)2D in maternal plasma. CaBP in maternal duodenum increased by the administration of 1,25-(OH)2D3 or 1,24,25-(OH)3D3. In contrast, 24,25-(OH)2D3 injections to TPTX mothers were ineffective. In both placenta and fetal membranes, CaBPs decreased by 20% in TPTX mothers and were normalized only in 1.25-(OH)2D3-treated TPTX mothers. In the fetal intestine, CaBP variations paralleled those of maternal duodenal CaBP. The data indicate that plasma levels of 1,25-(OH)2D in TPTX pregnant rats are partly under the control of maternal parathyroid glands, and they support that even in pregnancy, the CaBP concentration in maternal duodenum may well reflect the 1,25-(OH)2D status of the mother. The CaBP synthesis in placenta and fetal membranes are vitamin D-dependent, and their regulation differs from that of intestinal CaBP. It app]ears that 1 alpha-hydroxylase activities of the fetoplacental unit (placenta and fetal kidney) are blunted in TPTX animals and that CaBP synthesis in the fetus depends on the presence of 1 alpha-hydroxylated vitamin D3 metabolites in the mother.

Histomorphometric evaluation of the effects of intermittent 1,25-dihydroxycholecalciferol administration on cortical bone remodeling in adult dogs

The effects of intermittent low doses (1.25 mug daily, administered intravenously for 6 days and withdrawn for 14 days for 3 complete cycles) of 1,25-dihydroxycholecalciferol (1,25-[OH](2)D(3)) on cortical bone were determined and compared in ribs with steady state and regionally accelerated remodeling in adult intact female dogs. The bone changes were analyzed by dynamic bone histomorphometric methods, using tetracycline and DCAF (2,4 BIS) N, N' di (carboxymethyl) (amino methyl fluorescein) in vivo double labeling of bones before treatment and after 60 days of intermittent 1,25-(OH)(2)D(3) administration. Serum calcium and phosphorus levels increased during 1,25-(OH)(2)D(3) administration. Urinary hydroxyproline excretion increased during the first interval of 1,25-(OH)(2)D(3) administration but was not changed significantly during the last two intervals. In normal cortical bone (11th rib) following the administration of 1,25-(OH)(2)D(3) there was a marked decrease in the activation frequency, bone formation rate, osteoid seam thickness, seam circumference, and mean appositional rate. Although recruitment of new remodeling sites was decreased after 1,25-(OH)(2)D(3), previously existing remodeling units continued to completion. These effects resulted in a preponderance of mature osteons in normal cortical bone. The morphometric changes in cortical bone (9th rib) exposed to both 1,25-(OH)(2)D(3) and periosteal elevation were characterized by a marked increase in both the activation frequency and bone formation rate and associated with a decrease in the osteon formation time. Other morphometric parameters that were increased included radial closure rate, numbers of osteoid seams and resorption cavities, ratio of bone resorbing to forming sites, percentage labeled and circumference of osteoid seams, and total and cortical bone areas. The combined effect of periosteal elevation and 1,25-(OH)(2)D(3) were markedly different from those observed with 1,25-(OH)(2)D(3) alone. These findings suggest that the rapid bone turnover induced by tissue injury will mask or alter the effects of hormones on bone remodeling when studied over a relatively short period of time.

Effect of vitamin D sterols and dietary magnesium on calcium and phosphorous homeostasis

Calcium (Ca) and phosphorus (P) metabolism were studied in vitamin D-deficient rats as vitamin D status and dietary magnesium (Mg) were varied. Rats given normal (0.03%) or high (0.2%) Mg diets received either vehicle, vitamin D3 (1,650 pmol/day), or 1,25-dihydroxyvitamin D3 (60 pmol/day) for 9 days. In vitamin D-deficient rats, high dietary Mg lowered intestinal Ca absorption from 40 +/- 5 to 11 +/- 5%; P absorption decreased 50%. Treatment with 1,25-dihydroxyvitamin D3 prevented the Mg-induced fall in absorption; vitamin D3 did so only for the first 6 days. The total Ca and Mg (Ca + Mg) absorbed (mM/day) decreased from 0.85 +/- 0.050 mM/day to 0.14 +/- 0.10 with the high dietary Mg; 1,25-dihydroxyvitamin D3 treatment raised Ca + Mg absorption regardless of diet Mg; high dietary Mg raised serum Ca despite a decreased intestinal Ca absorption and urinary Ca; treatment with either sterol had no added calcemic effect. These results are consistent with two processes for intestinal Ca and P transport: one vitamin D-dependent and the other non-vitsamin D-dependent and inhibited by high dietary Mg. Also high dietary Mg increases serum Ca, perhaps by affecting bone resorption.

Effect of 1 alpha-hydroxyvitamin D3 on the glucose and calcium metabolism in genetic obese mice

In summary, it is demonstrated, for the first time, that there is a marked reduction of bone mass in ob/ob mice and this was restored by the treatment with 1 alpha-OH-D3. The effect of the sterol was accompanied by the improvement of hyperglycemia, hyperinsulinemia, and fat tissue responsibility to hormones. Thus, it is of interest to study obesity in terms of calcium homeostasis.

Effect of 1 alpha-hydroxycholecalciferol on bone mass and composition of cortical bone in adult male rats

High daily oral doses of 10 micrograms 1 alpha-hydroxycholecalciferol (1 alpha-OHD3) administered to adult rats produced toxic effects such as loss of body weight, hypercalcemia and bone resorption. However, small (0.09 microgram) and moderate (0.9 microgram) daily doses of 1 alpha-OHD3 did not produce toxic effects during six weeks of observation. Serum calcium level was only slightly raised, but bone mass, bone mineral and organic matter contents, including collagen and nucleic acids of the cortical bone matrix, significantly increased, while the amount of glycosaminoglycans was reduced. Treatment with small daily doses of 1 alpha-OHD3 (0.09 microgram/day for six weeks) produced a more pronounced effect on the variables studied than did the moderate dosage (0.9 microgram). 1 alpha-OHD3 promotes new bone formation in the mature rat skeleton after conversion to 1,25 dihydroxycholecalciferol [1,25(OH)2D3] in the liver, probably by exerting a direct effect on bone tissue rather than through indirect hormonal events.

1,25-dihydroxycholecalciferol stimulates osteoclasts in rat bones in the absence of parathyroid hormone

Three experiments were carried out to test the time course of effects of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] on the ultrastructural morphometry of osteoclasts. The addition of lactose to a vitamin D-deficient diet with a high calcium and phosphate content, fed to weanling rats for 4 weeks, ensured normacalcemia and normophosphatemia and allowed thyroparathyroidectomy without ill effects. In these vitamin D-deficient thyroparathyroidectomized rats, iv injection of 50 ng 1,25-(OH)2D3 resulted in significant changes in the osteoclasts in the metaphysis of the tibiae compared to those in corresponding controls; the size of these cells, their nuclei, ruffled borders, and clear zones enlarged after 6 h and the number of osteoclasts increased after 48 h. Serum calcium and serum phosphate levels increased after 12 h in one experiment, but not in a second experiment. Serum 25-hydroxyvitamin D and serum immunoreactive parathyroid hormone levels were undetectable. Mineralization of metaphyseal bone matrix was normal, as quantified by histomorphometry. When, dependent on the mineral content in the diet, mineralization was impaired and the volume density of the osteoid seams was increased, activation of osteoclasts by 1,25(OH)2D3 was not seen until 12--24 h after injection. It is concluded that a physiological dose of 1,25-(OH)2D3 stimulates the activity of osteoclasts in the absence of parathyroid hormone.

An examination of the importance of 24-hydroxylation to the function of vitamin D during early development

To investigate the biological importance of 24R-hydroxylation of 25-hydroxyvitamin D to the early development of rats, the potency of 24,24-difluoro-25-hydroxyvitamin D3 had been compared to that of 25-hydroxyvitamin D3 in young rat pups born to vitamin D-deficient mothers. 24,24-Difluoro-25-hydroxyvitamin D3 and 25-hydroxyvitamin D3 were equally active in stimulating active calcium transport in the intestine, maintaining normal concentrations of calcium and phosphorus in the plasma and promoting bone growth and mineralization. These results provide strong evidence that the presence of a hydroxyl group at the 24 position of vitamin D3 is not required for the maintenance of calcium-phosphate homeostasis during growth and in the development and mineralization of bone.

[Duodenal absorption of calcium in rats treated with 25 OHD3, diphosphonates and synthetic anabolics]

In this study the authors developed new technics of study of duodenal absorption of calcium in rats: atomic absorption spectrophotometry, and dialysis to equilibrium. We considered that the main factors necessary for evaluation of duodenal absorption of calcium are the serum calcium, the calcium and alkaline phosphatase present in the duodenal cells and the calcium-binding proteins. The authors demonstrate that these factors are highest in rats treated with 25 OHD3 and norandrostenolone decanoate, than in control rats. In rats treated with diphosphonate, on the contrary, they obtained a reduction in the values of calcium and alkaline phosphatase contained in the duodenal cells.

Effect of 1,25 dihydroxyvitamin D3 on insulin secretion

Recent autoradiographic studies demonstrated that B-cells concentrate 1,25 (OH)2 D3 in their nuclei, suggesting a genomic action on B-cell function. This study was undertaken to investigate the effects of 1,25 (OH)2 D3 on insulin secretion in vitamin D-deficient rats. Mature vitamin D-deficient rats were injected with 1,25 (OH)2 D3 or the ethanol-isotonic saline vehicle. Administration of 1,25 (OH)2 D3 to 10 rats resulted in a 17 microunits/ml (113%) increase in insulin levels and 0.9 mg/dl (16%) increase in plasma calcium. No changes were found in insulin or calcium levels in 5 control rats given vehicle alone. A group of vitamin D-deficient rats with plasma calcium levels of 5.4 +/- 0.1 mg/dl had insulin levels that were the same as those observed in a group of vitamin D-deficient rats with plasma calcium levels of 6.3 +/- 0.1 mg/dl. The difference in calcium levels between these two groups is similar to the increase in plasma calcium found after 1,25 (OH)2 D3 administration. The results of these studies indicate that 1,25 (OH)2 D3 action on pancreatic B-cells affects insulin secretion. Since insulin increases synthesis of 1,25 (OH)2 D3, the existence of a feedback loop between B-cells and kidney proximal tubule cells is suggested.

The effect of inhibitors of protein and RNA synthesis on 1 alpha,25-dihydroxyvitamin D3-dependent calcium uptake in cultured embryonic chick duodenum

To determine whether 1 alpha, 25-dihydroxyvitamin D3-dependent increases in intestinal calcium uptake require de novo protein and RNA synthesis, the effects of several inhibitors of these processes have been re-examined in vitro using cultured embryonic chick duodenum. To minimize the contributions of antibiotic toxicity to the interpretation of results, care was taken to examine inhibitor effects at early times after the onset of the 1 alpha, 25-dihydroxyvitamin D3 response. Cycloheximide at a concentration of 5 microM blocked hormone-dependent calcium uptake at all times examined (6 to 24 h). Actinomycin D was similarly effective at 6 to 12 h. The effects of cycloheximide were totally reversible while actinomycin D inhibition was only partially reversible. These compounds inhibited protein or RNA synthesis by 68.4 +/- 1.4 and 51.4 +/- 1.1%, respectively. Anisomycin, another inhibitor of polypeptide chain elongation and alpha-amanitin, an inhibitor of RNA polymerase I, also blocked 1 alpha, 25-dihydroxyvitamin D3-dependent calcium uptake after 12 h in culture. These results further strengthen the hypothesis that 1 alpha, 25-dihydroxyvitamin D3 stimulates intestinal calcium transport via a nuclear mechanism involving new gene expression.