Systemic inhibition of tumor promoter-induced ornithine decarboxylase in 1 alpha-hydroxyvitamin D3-treated animals

Topical application of 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3], an active form of vitamin D3, was previously shown to inhibit the induction of ornithine decarboxylase (ODC) and tumor promotion by tumor promoters in mouse skin. In the present study, this observation in skin was extended to other tissues, such as the stomach, colon, and liver, using 1 alpha-hydroxyvitamin D3 [1 alpha (OH)D3], which is converted to 1 alpha,25(OH)2D3 in the liver without hormonal control and thus evokes the systemic effects, if any, of 1 alpha,25(OH)2D3. When mice were given 1 alpha (OH)D3 at a dose of 5 micrograms by gastric tube, their plasma level of 1 alpha,25(OH)2D3 increased to a peak of about 18-fold the normal level after 12 h, followed by hypercalcemia (about 14 mg/dl), which reached a peak on Days 2 to 3. In 1 alpha (OH)D3-treated mice, induction of epidermal ODC by 12-O-tetradecanoylphorbol-13-acetate was markedly inhibited, the inhibition being maximal 2 to 4 days after 1 alpha (OH)D3 administration. ODC induction in the glandular stomach mucosa of rats by NaCl, a tumor promoter in stomach carcinogenesis, was also inhibited dose and time dependently by 1 alpha (OH)D3. Similarly, 1 alpha (OH)D3 treatment of rats markedly inhibited the induction of ODC in the colon mucosa by deoxycholate, a tumor promoter of colon carcinogenesis, and of ODC in the liver by phenobarbital, a promoter of liver carcinogenesis. These results suggest that an active form of vitamin D3 has a systemic inhibitory effect on induction of ODC activity by tumor promoters.

Hexokinase and adenylate kinase activities in aorta, heart muscle and skeletal muscle from uraemic rats

The effect of parathyroidectomy and/or vitamin D on the development of arterial and myocardial lesions was studied in rats with moderate uraemia. The activities of hexokinase and adenylate kinase in the aorta, myocardium and skeletal muscle were measured and the incidence of aortic calcification and muscle cell necrosis determined. There was a decreased hexokinase activity in the aorta, myocardium and skeletal muscle from uraemic rats. Adenylate kinase showed an increased activity in the same tissues. Parathyroidectomy as well as I-alpha-hydroxycholecalciferol in a dose of 3 ng/100 g b.w. normalized these activities to a great extent. This effect did not occur when 10 ng/100 g b.w. was given. Parathyroidectomy in combination with a low dose of I-alpha-OH-D3 reduced the incidence of myocardial necrosis. Aortic calcifications were found in uraemic animals given 10 ng/100 g b.w. of I-alpha-hydroxycholecalciferol. In this group increased activity of adenylate kinase was found in calcified aortae but not in non-calcified aortae. The study shows that uraemia causes metabolic changes in the aorta, myocardium, and skeletal muscle which may partly be prevented by parathyroidectomy and by low doses of vitamin D. It also indicates some parallelism between these metabolic changes and the development of histologically demonstrable lesions in the aorta.

Synthesis and biological activity of 1 alpha,23,25,26-tetrahydroxyvitamin D3

The metabolic pathway from 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25-(OH)2D3] to 1 alpha,25-dihydroxyvitamin D3-26,23-lactone includes the formation of 1 alpha,23,25-26-tetrahydroxyvitamin D3 [1 alpha,23,25,26-(OH)4D3]. The aim of the current study was to explore the as yet unknown biological properties of this vitamin D3 sterol. The four diastereoisomers of 1 alpha,23,25,26-(OH)4D3 were chemically synthesized. They were compared to 1 alpha,25-(OH)2D3 in terms of their affinity for the chick intestinal 1 alpha,25-(OH)2D3 receptor and their biologic activity in vivo (stimulation of intestinal calcium absorption and mobilization of calcium from bone in vitamin D-deficient rats). The 1,25-(OH)2D3 receptor binding affinities of 1 alpha,23(R)25(R)26-(OH)4D3, 1 alpha,23(S)25(S)26-(OH)4 D3, 1 alpha,23(S)25(R)26-(OH)4D3, and 1 alpha,23(R)25(S)26-(OH)4D3 were 11, 100, 216, and 443 times weaker than the binding affinity of 1 alpha,25-(OH)2D3, respectively. Compared to 1 alpha,25-(OH)2D3, the relative capacities of the 1 alpha,23,25,26-(OH)4D3 compounds to stimulate intestinal calcium absorption were 1/4 for 1 alpha,23(R)25(R)26-(OH)4D3; 1/19 for 1 alpha,23(S)25(S)26-(OH)4D3; 1/90 for 1 alpha,23(S)25(R)26-(OH)4D3; and 1/136 for 1 alpha,23(R)25(S)26-(OH)4D3. Maximal stimulation of intestinal calcium transport occurred 8 h after administration of vitamin D3 metabolites. Mobilization of calcium from bone was quantitated by serum calcium concentration measurements. The activities of 1 alpha,23(R)25(R)26-(OH)4D3, 1 alpha,23(S)25(S)26-(OH)4D3, 1 alpha,23(S)25(R)26-(OH)4D3, and 1 alpha,23(R)25(S)26-(OH)4D3 to increase serum calcium were estimated to be 4, 13, 43, and 69 times weaker than that of 1 alpha,25-(OH)2D3, respectively. These results illustrate the stereospecificity of the chicken intestine 1 alpha,25-(OH)2D3 receptor for binding of 1 alpha,23,25,26-(OH)4D3 and suggest that the 1 alpha,23,25,26-(OH)4D3 exerts its biological activity in the rat through an interaction with 1,25-(OH)2D3 receptors. In summary, the 1 alpha,23,25,26-(OH)4D3 had a markedly lower biological activity than 1 alpha,25-(OH)2D3.

Vitamin D affects proliferation of a murine T helper cell clone

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the biologically active form of vitamin D3, has been shown to inhibit the activation of T cell hybridomas and heterogeneous populations of mononuclear leukocytes. Because the response of various clones to 1,25(OH)2D3 may differ, we have examined the proliferative effects of the steroid on an antigen-specific cloned, nontransformed T helper cell line (D10.G4.1 [D10 cells]), and find that in contrast to these previous studies, the steroid is a potent stimulator of lectin-induced proliferation. In these experiments, D10 cells were incubated with concanavalin A and 1,25(OH)2D3, and although the lectin or steroid alone has minimal proliferative effects, their co-addition prompts up to a 50-fold increase in 3H-TdR incorporation at a concentration of 2.5 to 5 X 10(-9) M 1,25(OH)2D3, with significant mitogenesis occurring at 0.1 to 0.3 X 10(-9) M 1,25(OH)2D3. 25-Hydroxyvitamin D3 and 24,25(OH)2D3 have similar activity, but at concentrations two to three times greater than that of 1,25(OH)2D3, reflecting their relative affinities for the 1,25(OH)2D3 receptor. In addition, lectin treatment enhances 1,25(OH)2D3 receptor capacity fourfold to fivefold, an event coupled with the appearance of positive cooperativity. Although the steroid does not affect the quantity of bioassayable T cell growth factors as assessed by HT-2 cell proliferation, the expression of immunoreactive IL 2 receptors by lectin-activated D10 cells exposed to 1,25(OH)2D3 is enhanced. In contrast to its proliferative effect in the absence of IL 1, 1,25(OH)2D3 exerts biphasic effects on D10 replication when this monokine is present. Specifically, this steroid augments D10 proliferation at low concentrations of recombinant IL 1, but as the abundance of the monokine increases in the presence of 10(-10) to 10(-8) M 1,25(OH)2D3, the peak response of D10 cells to optimal IL 1 concentrations is diminished. Therefore, in this clone, 1,25(OH)2D3 presents itself as a regulator of T helper cell proliferation.

1,25-Dihydroxycholecalciferol regulates salivary phosphate secretion in cattle

The influence of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) on salivary inorganic phosphorus (Pi) concentration and secretion was studied in two groups of four heifers, the right parotid ducts of which were chronically fitted with a re-entrant cannula. In four heifers i.v. Pi loading (5 mmol/min for 2 h) induced hyperphosphataemia associated with a decrease in plasma 1,25-(OH)2D concentration and an increase in salivary Pi concentration and secretion. In four other heifers, daily 1 alpha-hydroxycholecalciferol injections (1 microgram/kg body wt per day for 3 days) induced hyperphosphataemia associated with an increase in plasma 1,25-(OH)2D concentration and a decrease in salivary Pi concentration and secretion. These treatments had no significant effect on salivary calcium concentration and secretion. Our results indicate that plasma 1,25-(OH)2D concentrations rather than phosphataemia regulate salivary Pi concentration and secretion in cattle.

An investigation of calcium intake, 1-alpha(OH)D3, and etidronate on bone

The synthetic metabolite of vitamin D3 [1 alpha(OH)D3] caused a significant plasma calcium elevation in rats only when dietary calcium was low. Animals given the low calcium diet (0.005%) had lower plasma parathyroid hormone (PTH) levels when the diet contained 1 alpha(OH)D3 and significantly higher levels than animals on a high calcium (0.95%) diet, with or without the vitamin. The nutritional stress of a low calcium diet without 1 alpha(OH)D3 resulted in a prolonged severe hypocalcemia and elevated serum PTH levels. A higher ash, phosphate, and calcium content was found in the bones of animals fed the high calcium diet, with no vitamin D3 that were given etidronate (EHDP). When animals received the same calcium diet with 1 alpha(OH)D3 supplementation, EHDP administration increased the percentage of bone ash but had no effect on ash weight. 1 alpha(OH)D3 or EHDP did not affect ash weight, dry fat free weight, and percentage of ash of bone of animals receiving a low calcium diet. The percentage of calcium and phosphorus in bone ash was similar among all groups, although the amounts per humerus were characteristically related to the calcium intake. There was approximately 20-25% less bone mineral and calcium and phosphorus in the humeri of low calcium intake animals than in animals provided an adequate dietary calcium.

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

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

Lack of influence of vitamin D deficiency on insulin release from the isolated pancreatic islets of rats

Pancreatic islets were isolated from young (100 g) and adult (390 g), normal and vitamin D deficient male Sprague-Dawley rats. The release of insulin from leucine-stimulated or glucose-stimulated islet was not altered by vitamin D deficiency. The in vitro addition of either 25-hydroxy- or 1,25-dihydroxyvitamin-D had no effect on insulin release from either normal or vitamin D deficient islets. We conclude that the earlier report (Normal et al., Science 209 (1980) 823-825) on vitamin D deficiency depressing insulin secretion from the perfused pancreas must be related to the vitamin's effect on insulin synthesis and not the islet's release of insulin.

Biological activity of vitamin D metabolites and analogs: dose-response study of 45Ca transport in an isolated chick duodenum perfusion system

We have previously reported that vascular perfusion of the normal vitamin D3-replete chick duodenum with physiological amounts of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] increases the unidirectional movement of 45Ca from the lumen to the venous effluent under conditions of normal (0.9 mM) Ca2+ concentrations in both the lumen and vascular perfusate [Endocrinology 115: 1476 1984)]. The purpose of the present study was to determine the dose responsivity of this perfused intestinal calcium transport system for 1,25(OH)2D3 and some structurally related congeners. The dose-response curve was biphasic for all compounds studied; for 1,25(OH)2D3 initial stimulation of transport was detected at only 30 pM [the plasma concentration of 1,25(OH)2D3 is normally 125 pM] while maximal stimulation was 154% above control at a concentration of 650 pM. Above 650 pM 1,25(OH)2D3 the stimulation fell off sharply and transport had returned to basal levels by 1.3 nM. The relative potency of the D homologs tested was respectively 1,25(OH)2D3: 10,000; 1-alpha-hydroxyvitamin D3: 400; 25-hydroxyvitamin D3: 200; 24R,25-dihydroxy-vitamin D3: 137; vitamin D3: 34; 5,6-trans-25-hydroxyvitamin D3: 3. These results establish the usefulness of the perfused intestinal calcium transport system to study the nongenomic actions of 1,25(OH)2D3 on intestinal calcium transport.

The effect of 1 alpha-hydroxyvitamin D3 on cell-mediated immunity in hemodialyzed patients

The immunoregulatory effect of 1 alpha-hydroxyvitamin D3 (1 alpha OHD3), a precursor form of active vitamin D3, was examined in hemodialyzed patients. Four weeks of oral administration of 0.5 micrograms/day 1 alpha OHD3 markedly enhanced the lymphoproliferative responses to mitogens without influencing lymphocyte counts or the ratios of lymphocyte subpopulations. In fact, these responses were nearly normal after treatment. These results suggest that deficiency of 1,25-dihydroxyvitamin D3 may play a role in the impairment of cellular immunity in hemodialyzed patients, and that administration of 1 alpha OHD3 may have therapeutic immunological benefit.

1 alpha(OH) vitamin D3 increases plasma aluminum in hemodialized patients taking AI(OH)3

1 alpha(OH) vitamin D3 at the dose of 6 micrograms per week was given for 4 weeks to 16 stable patients on chronic hemodialysis with a low dialysate aluminum while taking a constant dose of Al(OH)3. A significant increase of their plasma aluminum was observed from 1.2 +/- .25 mumol/l before 1 alpha(OH)D3 to 1.7 +/- .35 during the second fortnight of 1 alpha(OH)D3 administration and this increase surprisingly was maintained at 1.71 +/- .3 up to 6 weeks after 1 alpha(OH)D3 discontinuation. Increases in plasma calcium and decreases in plasma PTH were observed during 1 alpha(OH)D3 administration and these changes were correlated to the changes in plasma aluminum. It is concluded that the increase in plasma aluminum observed with 1 alpha(OH)D3 and after its discontinuation is either due to body aluminum burden redistribution or to increased aluminum intestinal absorption whatever the mechanism is, this effect should lead to close monitoring of plasma aluminum in uremic patients taking 1 alpha OH vitamin D3.

Bone changes in rats with adjuvant arthritis: treatment with 1 alpha-hydroxycholecalciferol

Adjuvant arthritis was induced in female Lewis rats by the injection of Mycobacterium butyricum in mineral oil in a hindpaw. Bone changes due to polyarthritis were evaluated in the tibia metaphyseal region of the noninjected hind leg. A decrease in bone mass and mineral content was observed in the affected bone. accompanied by a marked increase in bone resorption. Non-arthritic and arthritic rats were treated with the synthetic vitamin D analogue, 1 alpha-hydroxycholecalciferol (0.01 to 1.0 micrograms/kg/day orally) for 28 days. Treatment resulted in a small increase in bone weight and mineral content in the non-arthritic rats. Arthritic rats exhibited a larger increase in bone weight, hydroxyproline and calcium content. These beneficial effects were correlated with the ability of 1 alpha-hydroxycholecalciferol to increase extracellular calcium and phosphorus levels, as measured by the increased urinary excretion of calcium and inorganic phosphate and by the increase in serum calcium. Bone resorption and new bone formation were not affected by the treatment.

Hydroxyproline/creatinine ratios as estimates of bone resorption in early postmenopausal women. Fasting and 24-h urine samples compared

Ratio of urinary hydroxyproline/creatinine excretion is often used as an index of bone resorption. To establish the difference between the fasting urinary content (FU-HPR/CR) and the 24-h urinary excretion (24 h-U-HPR/CR) we determined hydroxyproline and creatinine in specimens from a group of early postmenopausal women. One hundred and eighty-six early postmenopausal women were randomized into 10 groups receiving various doses of sequential female sex hormones and/or 1,25(OH)2D3, 0.25 microgram per day, or placebo. In all groups there were parallel changes of FU-HPR/CR and 24 h-U-HPR/CR, and in all groups treated with oestrogens the values decreased significantly. The changes in FU-HPR/CR were more pronounced than in the 24-h-U-HPR/CR, which indicates that FU-HPR/CR is a more sensitive marker of changes in bone resorption. The strong correlation between the mean values of 24-h-U-HPR/CR and those of FU-HPR/CR suggests that both methods are convenient for evaluating changes during long-term studies in groups of patients. The correlation on an individual basis is weak. The substantial intraindividual variation in 24-h-U-HPR/CR, (34.6%) indicates that FU-HPR/CR (CV = 17.0%) is the more valid variable for individual patients.

Vitamin D metabolites stimulate phosphatidylcholine transfer to renal brush-border membranes

The phosphatidylcholine content of both the intestinal and renal brush-border membranes and ion transport are affected by 1,25-dihydroxycholecalciferol (1,25(OH)2D3). To investigate the mechanism of this effect, liposomes were prepared containing self-quenching concentrations of fluorescent phospholipid derivatives. When these liposomes were incubated with rat renal brush-border membrane vesicles, an immediate increase in the relative fluorescence of N-4-nitrobenz-2-oxa-1,3-diazole phosphatidylcholine (NBD-PC) was detected, indicating transfer of NBD-PC into a non-quenched membrane. Addition of 1,25(OH)2D3 to the liposomes produced a dose-dependent stimulation of NBD-PC transfer to the acceptor brush-border membrane vesicles. Peripheral fluorescence was visible when the brush-border membrane vesicles were viewed with a fluorescent microscope. Using brush-border membrane vesicles from kidneys of vitamin D-deficient animals, quantitation of lipid transfer revealed a 1,25(OH)2D3 (10(-7) M) stimulation of NBD-PC transfer from 1.38 +/- 0.27 to 2.07 +/- 0.26 micrograms/h, and of PC transfer, assessed by vesicle phosphatidylcholine content, from 49.7 +/- 12 to 57.3 +/- 12 micrograms/mg protein per h (P less than 0.05). There was no significant transfer of N-(lissamine rhodamine B sulfonyl)dioleoylphosphatidylethanolamine (N-Rh-PE). In the absence of hormone, the amount of NBD-PC transferred to brush-border membrane vesicles prepared from normal rats was significantly greater than that transferred to brush-border membrane vesicles prepared from vitamin D-deficient animals (2.12 +/- 0.02 vs. 1.39 +/- 0.27 micrograms of NBD-PC/h, P less than 0.05). Both physiologic and pharmacologic concentrations of 1,25(OH)2D3 stimulated NBD-PC transfer with maximum response at 10(-14) M (2.98 +/- 0.15 micrograms/h). 24,25-Dihydroxycholecalciferol and 25-hydroxycholecalciferol (25(OH)D3) also stimulated transfer, although dose-response curves were less effective than for 1,25(OH)2D3. Cortisol and vitamin D-3 did not stimulate transfer. 1,25(OH)2D3 did not stimulate NBD-PC transfer between liposome populations.

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

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 1 alpha-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 1 alpha-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.

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

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

Effect of long-term administration of 1,25-dihydroxyvitamin D3 and 1 alpha-hydroxyvitamin D3 on the calcium content of the aorta, heart and kidney of normal and uremic rats

Studies in uremic rats were performed to see whether or not the long-term administration of therapeutical doses of 1,25-Dihydroxyvitamin D3 or 1 alpha-hydroxyvitamin D3 would induce histological changes in the aorta or increase the calcium content of the aorta or the heart. In contrast to observations of others, no effect of both vitamin D sterols could be observed on both investigated tissues. However, the remnant kidneys of the rats treated with both vitamin D compounds showed a significantly increased calcium content. According to these results one cannot exclude that the chronic application of active vitamin D metabolites has induced a calcium deposition in the remnant kidney. This finding deserves special attention, although we found, on the other hand, no evidence that an underlying arterial disease is aggravated by this therapy.

Observation on the use of 1 alpha-hydroxyvitamin D3 in the prevention of bovine parturient paresis: the effect of a single injection on plasma 1 alpha-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, calcium, and hydroxyproline

Israeli Friesian cows in the third or later lactation, were injected intramuscularly with 1 alpha-hydroxyvitamin D3 in propylene glycol. Plasma 1 alpha-hydroxyvitamin D3 peaked 24 to 48 h after 700 micrograms of the drug was injected and decreased to the initial concentration 4 d later. The disappearance rate of 1 alpha-hydroxyvitamin D3 from the blood was .330 d-1 (biological half-life of 2.1 d). Plasma 1,25-dihydroxyvitamin D3 peaked 24 to 48 h after the injection and approached the initial concentration 5 to 7 d later. Plasma calcium increased within 24 h, reached a plateau at 4 to 6 d, and then decreased. Administration of 700 micrograms 1 alpha-hydroxyvitamin D3 resulted in higher plasma 1,25-dihydroxyvitamin D3 and calcium concentrations than when 350 micrograms of the drug was injected. 1 alpha-Hydroxyvitamin D3 did not affect plasma hydroxyproline. The injection of 700 micrograms 1 alpha-hydroxyvitamin D3 52 to 36 h before parturition resulted in a greater increase in plasma 1,25-dihydroxyvitamin D3 than that obtained with 350 micrograms. In both groups 1,25-dihydroxyvitamin D3 peaked 24 h after injection, as opposed to the controls, which peaked 72 h postpartum. At parturition, the 700-micrograms dose resulted in a slight hypercalcemia; the 350-micrograms dose moderated the hypocalcemia prevalent during this period, whereas in controls hypocalcemia was more pronounced. In cows injected with 700 micrograms, hypercalcemia was observed until the 15th d postpartum. Plasma hydroxyproline was elevated in all cows 48 to 72 h after parturition, but the increase was smaller in animals injected with 1 alpha-hydroxyvitamin D3.(ABSTRACT TRUNCATED AT 250 WORDS)

1 alpha,25-Dihydroxyvitamin D3 (calcitriol) stimulates proliferation of human circulating monocytes in vitro

Previous studies demonstrated that human circulating monocytes can proliferate in vitro when incubated with lectin-induced factor(s) from lymphocytes [(1985) Biochem. Biophys. Res. Commun., in press]. This study shows that human monocytes were induced to proliferate when incubated with 1 alpha,25-dihydroxyvitamin D3 (calcitriol) at physiological concentrations. The optimal dose was about 10 nM. Proliferative activity was examined both by measuring the [3H]thymidine incorporation and by counting cell nuclei. Among other derivatives of vitamin D3, 1 alpha,24R-dihydroxyvitamin D3 and 1 alpha,24R,25-trihydroxyvitamin D3 stimulated mitotic activity of monocytes. Addition of both calcitriol and lectin-stimulated lymphocyte-conditioned medium to the monocyte culture had an additional effect on the mitotic activity of monocytes.

The effect of 1 alpha-hydroxyvitamin D3 on primary antibody formation in mice

The immunoregulatory effect of 1 alpha-hydroxyvitamin D3, a precursor form of active vitamin D3 (1,25-dihydroxyvitamin D3), was examined in three different kinds of experimental systems in mice. Oral administration of 0.05 and 0.2 micrograms/kg of 1 alpha-hydroxyvitamin D3 augmented the primary immune response induced by immunization with 1 X 10(7) sheep erythrocytes, although it did not influence a maximal level of antibody formation induced by immunization with 5 X 10(8) sheep erythrocytes. The same treatment also restored the immune response depressed by restraint-stress. Furthermore, 1 alpha-hydroxyvitamin D3 suppressed the anti-dinitrophenyl plaque-forming cell response enhanced by colchicine injection to near the normal level. These results suggest that 1 alpha-hydroxyvitamin D3 enhanced or suppressed the immune response through activating helper and suppressor cells in dependence on the magnitude of the response.

Aspirin inhibition of 1 alpha-hydroxyvitamin D3 or parathyroid hormone induced hypercalcemia in vivo in rats. A mechanism independent of prostaglandin biosynthesis inhibition

The interactions of calcium-regulating hormones, active forms of vitamin D and parathyroid hormone, and aspirin were studied in rats. Aspirin, a prostaglandin biosynthesis inhibitor, abolished the hypercalcemia induced by 1 alpha-hydroxyvitamin D3 at 20, 50 and 100 mg/kg p.o. in parathyroidectomized or thyroparathyroidectomized rats with or without vitamin D deficiency, and in thyroparathyroidectomized plus nephrectomized rats. Aspirin did not affect the stimulation of intestinal calcium absorption by 1 alpha-hydroxyvitamin D3. By contrast, indomethacin, another prostaglandin biosynthesis inhibitor, did not affect hypercalcemia or stimulation of intestinal calcium absorption by 1 alpha-hydroxyvitamin D3. Aspirin also abolished the hypercalcemic action of parathyroid hormone in rats with or without intact thyroparathyroid glands. Moreover, aspirin alone caused hypocalcemia in rats with intact thyroparathyroid glands. Indomethacin had no effect in either of these systems. These data suggest that aspirin may inhibit bone resorption by the active form of vitamin D or parathyroid hormone via a mechanism independent of prostaglandin biosynthesis inhibition.

Vitamin D metabolites regulate osteocalcin synthesis and proliferation of human bone cells in vitro

The effects of six natural vitamin D metabolites of potential biological and therapeutic interest, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3), 25-hydroxyvitamin D3 (25-OH-D3), 24R,25-dihydroxyvitamin D3 (24R,25-(OH)2D3), 1,24R,25-trihydroxyvitamin D3 (1,24R,25-(OH)3D3), 25S,26-dihydroxyvitamin D3 (25S,26-(OH)2D3) and 1,25S,26-trihydroxyvitamin D3 (1,25S,26-(OH)3D3) on cell replication and expression of the osteoblastic phenotype in terms of osteocalcin production were examined in cultured human bone cells. At a dose of 5 X 10(-12) mol/1, 1,25-(OH)2D3 stimulated cell proliferation, whereas at higher doses (5 X 10(-9)-5 X 10(-6) mol/1) cell growth was inhibited in a dose-dependent manner. The same pattern of effects was seen for the other metabolites in a rank order of potency: 1,25-(OH)2D3 greater than 1,25S,26-(OH)3D3 = 1,24R,25-(OH)3D3 greater than 25S,26-(OH)2D3 = 24R,25-(OH)2D3 = 25-OH-D3. Synthesis of osteocalcin was induced by 1,25-(OH)2D3 in doses similar to those required to inhibit cell proliferation. Biphasic responses were observed for some of the metabolites in terms of osteocalcin synthesis, inhibitory effects becoming apparent at 5 X 10(-6) mol/1. The cells did not secrete osteocalcin spontaneously. These results indicate that vitamin D metabolites may regulate growth and expression of differentiated functions of normal human osteoblasts.

The effect of 1 alpha-hydroxyvitamin D2 on calcium metabolism in glucocorticoid-treated rats

Intestinal calcium transport and renal calcium and phosphate excretion have been measured in normal and prednisolone-treated rats. Prednisolone treatment reduced intestinal calcium transport and increased phosphate excretion, causing a reduction in serum phosphate. Both 1 alpha-hydroxyvitamin D2 and 1 alpha-hydroxyvitamin D3 normalized phosphate excretion, whereas 1 alpha-hydroxyvitamin D3 was not fully effective in serum phosphate. Prednisolone treatment also caused a decreased bone density that was prevented both with 1 alpha-hydroxyvitamin D2 and 1 alpha-hydroxyvitamin D3. 1 alpha-hydroxyvitamin D2 appeared at least as effective as 1 alpha-hydroxyvitamin D3 in correcting the bone disturbance.

Early and direct effect of 1,25-dihydroxycholecalciferol on calcium uptake by duodena of rachitic chicks

Injection of 1,25 dihydroxycholecalciferol (1,25(OH)2D3, 10 micrograms) directly into the in situ ligated duodenal loop of rachitic chicks significantly elevated the tissue accumulation of 47Ca within 20-30 min. The transfer of 47Ca from lumen to blood, during the same time period, was not increased nor was there any measurable intestinal calcium-binding protein synthesized. Lesser amounts of 1,25(OH)2D3 (1 or 5 micrograms) did not result in any statistically significant elevation of 47Ca tissue accumulation, nor did they have any effect on 47Ca transfer from lumen to blood (transmural). Ten micrograms of 1,24R,25(OH)3D3 was similarly effective in elevating tissue accumulation, whereas 24R,25(OH)2D3 and 25(OH)D3 were not. These results provide additional evidence for an early and direct action of 1,25(OH)2D3 in altering intestinal epithelial membrane transport prior to the induction of synthesis of specific transport proteins.

Antirachitic activity of 1 alpha-hydroxyergocalciferol and 1 alpha-hydroxycholecalciferol in rats

Weanling vitamin D-deficient rats fed a high calcium, low phosphate diet were injected daily with 1 alpha-hydroxyergocalciferol or 1 alpha-hydroxycholecalciferol at doses of 2.5, 25 or 250 ng. Intestinal calcium and phosphate transport, serum phosphorus level, epiphyseal plate calcification, and percent femur ash increased as a function of the dose. Both compounds were equally effective in eliciting these responses demonstrating their equivalency as antirachitic compounds.

1,25 Dihydroxyvitamin D causes attenuation of cyclic AMP responses in monocyte-like cells

The U937 cell is a human monocyte-like line which possesses 1,25(OH)2D receptors. To study 1,25(OH)2D actions in these cells we have measured the cAMP produced by U937 cells during 10 minute stimulus by the beta-adrenergic agonist isoproterenol or by forskolin. cAMP produced by isoproterenol is 6 times that of forskolin. When cells are exposed to 1,25(OH)2D for at least 8 hours the cAMP produced is decreased up to 55%. This attenuative effect of 1,25(OH)2D is dose dependent with an EC50 of 10(-10)M. Other vitamin D metabolites are less than 1/100th as potent.

Effects of 1 alpha OHD2 on bone tissue. Studies of 1 alpha OHD2 and 1 alpha OHD3 in normal rats and in rats treated with prednisolone

Three months old male rats were fed a diet containing 0.3% calcium and 0.5% phosphate. Prednisolone was added to the diet at a dose of 1.5 mg a day and the effect of oral treatment with 0.5 micrograms 1 alpha OHD2 or 0.5 micrograms 1 alpha OHD3 was studied. After 6 weeks rats given prednisolone had a lower bone mass and bone density. The serum phosphate concentration was also lower. Rats given 1 alpha OHD3 had an increased serum calcium concentration even when simultaneously treated with prednisolone. 1 alpha OHD2 did not cause hypercalcaemia. The decrease in bone density caused by prednisolone was prevented by the administration of 1 alpha OHD2. Rats receiving 1 alpha OHD3 together with prednisolone still exhibited a lower bone density. Furthermore, 1 alpha OHD3 decreased bone mass in normal rats and caused a higher mean value of osteoclasts/area whereas 1 alpha OHD2 reduced the number of osteoclasts/area. The study indicates that 1 alpha OHD2 is an effective vitamin D analogue with a lower tendency to cause bone resorption.

Influence of 1,25-dihydroxyvitamin D3 on cultured osteogenic sarcoma cells: correlation with the 1,25-dihydroxyvitamin D3 receptor

We have characterized the effects of the steroid hormone 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] on a series of rat osteogenic sarcoma cell lines of increasing osteoblastic-like nature (ROS 24/1, ROS 2/3, and ROS 17/2.8). When these cells were grown in monolayer culture in the presence of 10 nM 1,25-(OH)2D3, there was a dramatic and selective inhibition of proliferation in the ROS 17/2.8 line. Similar concentrations of other vitamin D metabolites did not elicit this effect. Furthermore, the aggregated cuboidal ROS 17/2.8 cells showed a marked change after 6 days of treatment with 10 nM 1,25-(OH)2D3 to an apparently less transformed spindle-like morphology. In contrast, ROS 2/3 displayed only a slight morphological alteration, and ROS 24/1 was unchanged by treatment with 1,25-(OH)2D3. Anchorage-independent growth studies performed in soft agar indicated that 1,25-(OH)2D3 inhibited colony formation to the greatest degree in ROS 17/2.8, with a lesser effect in ROS 2/3. Based upon analyses by sucrose gradient centrifugation, DNA cellulose chromatography, and saturation of specific binding, the level of the 1,25-(OH)2D3 receptor was quantitated in these cells. ROS 17/2.8 cells possess 18,000 copies of the receptor per cell, while ROS 2/3 contains only 500 binding sites per cell, and no detectable high-affinity 1,25-(OH)2D3 receptor is found in ROS 24/1. The receptor in ROS cells is indistinguishable from other mammalian 1,25-(OH)2D3 receptors in that it is a DNA-binding protein that sediments on sucrose gradients at 3.3S, and specifically binds the hormone with high affinity (Kd = 2 to 3 X 10(-11) M). Since the biological responses of these three cell lines to 1,25-(OH)2D3 exhibit a strong correlation with the respective number of receptor molecules per cell, we propose that the actions of this hormone are mediated by the specific 1,25-(OH)2D3 receptor.

Inhibitory effects of active vitamin D preparations on PTH secretion in rats

To study the effects of various vitamin D preparations on PTH secretion, serum calcium and urinary excretion of cAMP were monitored in conscious perfused rats, and the influences of a bolus iv injection of the preparations on these parameters were examined. Three hours after the administration of 0.25 microgram/kg (0.6 nmol/kg) of 1 alpha, 24(R)-dihydroxycholecalciferol [1 alpha, 24(OH)2D3], the urinary excretion of cAMP decreased to a level compatible with that of parathyroidectomized (PTX) rats (50% of initial value; p less than 0.05) with no change in the concentration of serum calcium (total and ionized). In PTX rats supplemented with bovine PTH (1 U/h), the vitamin D preparation showed no significant effects either on the urinary excretion of cAMP or on serum calcium. These effects were rather specific for active vitamin D preparations, i.e. 1 alpha, 25(OH)2D3 (0.25 micrograms/kg) and 1 alpha OHD3 (1.25-6.25 micrograms/kg). However, 24,25(OH)2D3 (up to 25 micrograms/kg) had no significant effect on these parameters. These results suggest that, in rats, active vitamin D preparations specifically inhibit PTH secretion without causing a significant increase in the serum calcium concentration, reflecting a direct feedback mechanism between active vitamin D metabolite and the parathyroid glands.

The aortic content of glycosaminoglycans, hydroxyproline and calcium in experimental uraemia with special reference to parathyroidectomy and vitamin-D treatment

The contents of the various glycosaminoglycan (GAG) fractions, hydroxyproline and calcium in the thoracic aorta from the rat were studied. The effect on these contents of induced uraemia (3/4 kidney resection) combined with parathyroidectomy and/or 1-alpha-hydroxycholecalciferol (1-alpha-OH-D3) treatment was evaluated. Confirming earlier results increased levels of GAGs (predominately of chondroitin and dermatan sulphate) were found in the aortae of uraemic rats. The present study showed that parathyroidectomy or treatment with 1-alpha-OH-D3 did not significantly further alter the aortic content of GAGs in uraemic rats. Arteriosclerotic changes (calcifying medial necrosis) were only found in non-parathyroidectomized uraemic rats given 1-alpha-OH-D3. The aorta from these rats had a lower total content of GAGs, mainly due to a decrease in hyaluronic acid, than that from uraemic rats without calcifications. The aortic content of calcium was lowest in uraemic parathyroidectomized rats. Treatment with 1-alpha-OH-D3 increased this content, which was augmented 100-200-fold when calcifications were present. No correlation between the aortic contents of calcium and GAGs was found. There was a statistically significant correlation between the aortic content of calcium and the serum calcium X phosphate product. A significantly lower content of hydroxyproline was found in uraemic non-parathyroidectomized rats given 1-alpha-OH-D3, especially in those with arteriosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological activity of glycosides of vitamin D3 and 1 alpha-hydroxyvitamin D3

For the first time, the biological activity of the newly synthesized glycosides of vitamin D3 and of 1 alpha(OH)D3 has been studied in rats, chickens, and Japanese quails. Glucosidation did not reduce the activity of vitamin D3. In chickens, vitamin D3 glucoside has an activity of 90% to 95% as compared to the aglycon. In rats vitamin D3 glucoside is equally active when given by intravenous or oral route. Glycosides of 1 alpha (OH)D3, however, show a lower activity in rats, chickens, and quails. 1 alpha (OH)D3 glucoside has about 10% activity of the free 1 alpha (OH)D3, while 1 alpha (OH)D3 cellobioside is without any activity in chickens. 1 alpha (OH)D3 glucoside might be of interest, due to its broader therapeutical dosage range.

Treatment with vitamin D or its analogues does not change body weight or blood glucose level in postmenopausal women

It has recently been stated that vitamin D analogues can reduce body weight in animal models. We evaluated the effect of treatment with vitamin D metabolites on the nutritional status of 238 postmenopausal women, who were participating in three double-blind placebo-controlled trials, the aim of which was to prevent or treat postmenopausal bone loss. After two years of treatment with vitamin D3, 2000 IU daily (n = 25), or l alpha OHD3, 0.25 micrograms daily (n = 23), or 1 year of treatment with 1,25 (OH)2D3, 0.25-0.50 micrograms daily (n = 40), no change in body weight or blood glucose level could be detected when compared to corresponding placebo treated groups (n = 150). It is concluded that the effect of vitamin D analogues on body weight is a phenomenon which is specific for an animal model and does not occur in man.

Vitamin D metabolites change the phenotype of monoblastic U937 cells

U937 is a human-derived lymphoma cell line that has monoblastic properties and high-affinity receptors for 1 alpha,-dihydroxyvitamin D3. Incubation of these cells with the vitamin D metabolite at 10 nM for 5 days produced marked stimulation in adherence and ingestion of Staphylococcus aureus (645% of control) and of C3b receptor (CR1) expression (292% of control) and a slight increase in hexose monophosphate shunt activity without changing cell growth rates or Fc fragment receptor expression. The changes in cellular association of S. aureus and the CR1 were detected as early as 48 hr of incubation and peaked between 3 and 5 days. Similar changes in the CR1 were induced by 25-hydroxy- and 24,25-dihydroxyvitamin D3 at micromolar concentrations. Dexamethasone, hydrocortisone, and progesterone had no effect on CR1 expression. U937 cells incubated in the presence of vitamin D metabolites exhibited a change in their phenotype. These results suggest that vitamin D metabolites may contribute to monocyte/macrophage differentiation.

Support of embryonic chick survival by vitamin D metabolites

The provision of 1,25-dihydroxyvitamin D3 as the only source of dietary vitamin D3 to laying hens failed to support normal embryonic development in their fertile eggs. Significant (P less than .001) improvement in embryonic survival to hatching in these eggs resulted from injections of 1,25-dihydroxyvitamin D3, 24,25-dihydroxyvitamin D3, 25-hydroxyvitamin D3, or 24,24-difluoro-25-hydroxyvitamin D3 prior to incubation. Maximum embryonic survival with lowest embryonic mortality was observed when 0.20 micrograms/egg of 1,25-dihydroxyvitamin D3 or 0.60 micrograms/egg 25-hydroxyvitamin D3 was injected. These results indicate that several forms of vitamin D, two of which cannot be converted to 24,25-dihydroxyvitamin D3, can provide this activity; and of the vitamin D compounds tested, 1,25-dihydroxyvitamin D3 may be the most active in supporting embryonic survival in the chick when delivered directly by injection.

Effect of low dose 1 alpha-hydroxycholecalciferol on glomerular filtration rate in moderate renal failure

Serial measurements of 51Cr edetic acid clearance were made over a period of one year in two groups of 8 children, in a double blind trial of 1 alpha-hydroxycholecalciferol (10 ng/kg/day) and calciferol (670 ng/kg/day). Glomerular filtration rate (GFR) at the beginning of the trial was 20-50 ml/min/1.73 m2; it rose in the children given 1 alpha-hydroxycholecalciferol (group A) after 6 months but was not appreciably different from the pretreatment value after 12 months. The GFR in the children given calciferol (group B) showed no significant difference at 6 or 12 months. Parathyroid hormone values fell markedly in group A after 6 months but not in group B. Quantitative bone histology improved considerably in group A but not in group B at 12 months. Low dose 1 alpha-hydroxycholecalciferol may be used effectively for renal osteodystrophy in children with moderate but stable renal failure without jeopardising renal function.

Kinetics of osteoclast formation: the significance of blood monocytes as osteoclast precursors during 1 alpha-hydroxycholecalciferol-stimulated bone resorption in the mouse

The significance of blood monocytes as a source of osteoclast precursors was investigated during 1 alpha-hydroxycholecalciferol-stimulated bone resorption in mice. Animals were given three injections of tritiated thymidine at 8 hourly intervals in order to label blood monocytes. The proportion of labelled monocytes was then compared with the proportion of labelled nuclei in osteoclasts, the formation of which was provoked by daily injections of 1 alpha-hydroxycholecalciferol, beginning 48 hours after the first injection of isotope. Although more than 60% of blood monocytes were labelled during the period of peak osteoclast formation, labelling of osteoclast nuclei in the metaphyseal endosteum of the femur never exceeded 8%. These results suggest strongly that the majority of osteoclast nuclei were derived from a source of unlabelled precursors, and that very few osteoclasts were derived directly from blood monocytes. Although few labelled osteoclasts were found, the proportion of labelled spindle shaped cells in the metaphyseal endosteum rose gradually to 16%. It is likely, therefore, that labelled mononuclear cells, possibly blood monocytes, were attracted to the endosteum where they formed a population of tissue macrophages. At this site they may participate in bone resorption, either individually or by providing a local pool of osteoclast precursors.

Effect of 1 alpha, 24 R,25-trihydroxycholecalciferol on isolated parathyroid cells secretion

In this work we have studied the action of the trihydroxylated vitamin D metabolite (1 alpha, 24 R,25(OH)3D3) on parathyrin secretion by isolated parathyroid cells. In contrast with the results obtained with mono and dihydroxylated vitamin D, 1 alpha, 24 R,25(OH)3D3 increased the secretion of parathyrin. The effective concentration of this metabolite was 1.54 X 10(-9)M for cells rat and 1.54 X 10(-10)M for human cells.

Biological activity assessment of the vitamin D metabolites 1,25-dihydroxy-24-oxo-vitamin D3 and 1,23,25-trihydroxy-24-oxo-vitamin D3

Two new metabolites of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], namely 1,25(OH)2-24-oxo-vitamin D3 and 1,23,25(OH)3-24-oxo-vitamin D3, have been prepared in vitro using chick intestinal mucosal homogenates. To investigate the binding of 1,25(OH)2-[23-3H]-24-oxo-D3 and 1,23,25(OH)3-[23-3H]-24-oxo-D3 to the chick intestinal receptor we have isolated both metabolites in radioactive form using an incubation system containing 1,25(OH)2-[23,24-3H))-D3 with a specific radioactivity of 5.6 Ci/mmol. Both metabolites were highly purified by using Sephadex LH-20 chromatography followed by high-pressure liquid chromatography (HPLC). Sucrose density gradient sedimentation analysis showed specific binding of both tritium-labeled metabolites to the chick intestinal cytosol receptor. Experiments were carried out to determine the relative effectiveness of binding to the chick intestinal mucosa receptor for 1,25(OH)2D3. The results are expressed as relative competitive index (RCI), where the RCI is defined as 100 for 1,25(OH)2D3. Whereas the RCI obtained for 1,25(OH)2-24-oxo-D3 was 98 +/- 2 (SE), the RCI for 1,23,25(OH)3-24-oxo-D3 was only 28 +/- 6 (SE). Also, the biological activity of both new metabolites was assessed in vivo in the chick. In our assay for intestinal calcium absorption, 1,25(OH)2-24-oxo-D3 was active at a dose level of 1.63 and 4.88 nmol/bird (at 14 h), whereas 1,23,25(OH)3-24-oxo-D3 showed only weak biological activity in this system. In our assay for bone calcium mobilization, administration of both new metabolites showed modest activity at the 4.88-nmol dose level, which was reduced at the 1.63-nmol dose level. The results indicate that biological activity declines as 1,25(OH)2D3 is metabolized to 1,24R,25(OH)3D3, 1,25(OH)2-24-oxo-D3, and then 1,23,25(OH)3-24-oxo-D3.

Renal effect of vitamin D metabolites: evidence for the essential role of the 25(OH) group

The effects of 1 alpha (OH)vitamin D3 [1 alpha (OH)D3] and 24,25(OH)2vitamin D3 [24,25(OH)2D3] on the phosphaturic action of parathyroid hormone (PTH) were studied in two groups of parathyroidectomized (PTX) rats. In group 1, PTX PTH-infused rats received intravenous 1 alpha (OH)D3, and in group 2, PTX PTH-infused rats received intravenous 24,25(OH)2D3. PTX PTH-infused rats served as controls. The effects of both vitamin D metabolites on renal PTH-activated adenylate cyclase (AC) were studied in vitro. In group 1, PTH increased fractional excretion of phosphate (CP/CIn) from 0.045 +/- 0.012 (+/- SE) to 0.263 +/- 0.011 (P less than 0.005). 1 alpha (OH)D3 failed to influence this response. In group 2, PTH increased CP/CIn from 0.055 +/- 0.008 to 0.289 +/- 0.027 (P less than 0.005). 24,25(OH)2D3 reduced the PTH-induced rise in CP/CIn from 0.289 +/- 0.027 to 0.192 +/- 0.021 (P less than 0.01) and decreased the urinary excretion of adenosine 3',5'-cyclic monophosphate. In vitro, 24,25(OH)2D3 blunted the PTH-activated AC, whereas 1 alpha (OH)D3 had no effect. These results show that 24,25(OH)D3, similar to two other 25(OH) metabolites of vitamin D-25(OH)vitamin D3 and 1,25(OH)2vitamin D3-suppresses the phosphaturic action of PTH, whereas 1 alpha(OH)D3, which is devoid of a 25(OH) group, lacks this effect. This suggests that a 25(OH) group is a prerequisite for the antiphosphaturic effect of vitamin D, whereas the 1 alpha (OH) group is not essential for this action.

The effect of 1 alpha-hydroxycholecalciferol on the placental transfer of calcium and phosphate in sheep

The calcium and phosphorus concentrations in foetal tissue or the placental transfer of 45Ca and 32P, or both, were studied in fifty-five control or 1 alpha-hydroxycholecalciferol (1 alpha-(OH)D3)-treated (0.1 micrograms/kg body-weight per d for 12 d) ewes between 77 and 140 d of gestation. Treatment resulted in a significant increase in the concentration of Ca and P in foetal tissues at all stages of gestation except at 140 d when, it is suggested, foetal mineralization may approach a maximum value. This increase in Ca and P concentration in foetal tissues was associated with an increased placental transfer of Ca, though at 111 and 120 d gestation this increase was not significant. P transfer, which was only measured at 140 d gestation, was also significantly higher in treated animals. The concentrations of Ca and P in both maternal and foetal plasma were increased significantly by the 1 alpha-(OH)D3 treatment. Whereas the concentration of Ca in the plasma of foetuses was always greater than in their dams, the concentration of plasma P in treated animals, unlike controls, was lower in foetuses than dams. This suggests that the increased placental transfer of P, unlike that of Ca, may be a passive rather than an active process.

23-Keto-25-hydroxyvitamin D3: a vitamin D3 metabolite with high affinity for the 1,25-dihydroxyvitamin D specific cytosol receptor

A new metabolite of 23,25-dihydroxyvitamin D3 has been generated with kidney homogenates prepared from vitamin D treated chicks. The metabolite was purified with three high-performance liquid chromatographic steps and was identified as 23-keto-25-hydroxyvitamin D3 by ultraviolet absorption spectroscopy, mass spectrometry, and chemical reactivity. The R stereoisomer of 23,25-dihydroxyvitamin D3 was 10-fold more effective as an in vitro precursor to 23-keto-25-hydroxyvitamin D3 than was the naturally occurring S stereoisomer. Approximately 500 ng of 23-keto-25-hydroxyvitamin D3 was necessary to produce the same degree of intestinal-calcium transport as 25 ng of vitamin D3--a difference of about 20-fold. 23-Keto-25-hydroxyvitamin D3 was not active at stimulating bone calcium resorption at the doses and times tested. This new vitamin D3 metabolite, however, had greater affinity than 25-hydroxyvitamin D3 to both the rat plasma vitamin D binding protein and the 1,25-dihydroxyvitamin D specific cytosol receptor. Heretofore, only 1 alpha-hydroxylated metabolites of 25-hydroxyvitamin D3 or analogues possessing a pseudo 1 alpha-hydroxy group were known to bind to the 1,25-dihydroxyvitamin D receptor with higher affinity than 25-hydroxyvitamin D3. Ketone formation at the 23 position, therefore, is the first side-chain modification of 25-hydroxyvitamin D3 that results in enhanced binding to the 1,25-dihydroxyvitamin D receptor binding protein.

Renal function and 1 alpha-hydroxyvitamin D3 in rabbits with normal renal function and renal insufficiency

The effect of 1 alpha-hydroxyvitamin D3 (1 alpha OHD3) on the renal clearance of creatinine was investigated in groups of rabbits with stable renal insufficiency and normal controls. Urine was collected in the two groups for two one-week periods during placebo treatment. Then, 1 alpha OHD3, 0.02 micrograms/kg BW/day, was administered orally and urine was collected during the next two weeks. Weekly blood samples were obtained. The treatment had no significant effect on the serum concentrations of calcium and phosphate in either group. Creatinine clearance decreased significantly in both groups during the 1 alpha OHD3 treatment (p less than 0.05), mainly due to a decreased urinary excretion of creatinine. It is suggested that changes in the renal tubular handling of creatinine caused by 1 alpha OHD3 may be the explanation of the observed effect.

Effect of 1 alpha-hydroxyvitamin D3 and dietary calcium and phosphate on the aortic mineral content in rabbits with mild azotemia

The effect of treatment with 1 alpha-hydroxycholecalciferol (1 alpha-OH-D3) and different diets on uremic arterial disease was studied. Three groups of rabbits with chronic renal failure (CRF) were kept on three diets with a low, medium or high content of calcium and phosphate. Half the rabbits in each group were treated for 18 weeks with 1 alpha-OH-D3, 0.02 micrograms/kg/day, without any significant changes in the serum concentrations of calcium or phosphate compared to placebo treatment. In the thoracic aorta, the content of calcium and phosphate was significantly increased in placebo-treated CRF rabbits on medium and high calcium and phosphate intakes compared to rabbits with normal renal function (p less than 0.05). The cholesterol content was unchanged. Treatment with 1 alpha-OH-D3 caused a further increase in the aortic content of calcium and phosphate in the CRF rabbits on medium and low calcium and phosphate intakes (p less than 0.05). No increase in the aortic cholesterol content was observed. The histological changes in the abdominal aorta consisted of medial proliferations with calcifications and intimal proliferations. The severity of these changes paralleled the mineral content of the thoracic aorta. Aggravation of uremic arterial disease may be a hitherto unrecognized side-effect of treatment with 1 alpha-OH-D3 in CRF.