Selective biological response by target organs (intestine, kidney, and bone) to 1,25-dihydroxyvitamin D3 and two analogues.

The hormonally active form of vitamin D, 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3] stimulates biological responses related to calcium homeostasis, cell differentiation, and immunomodulation in many target cells, including leukemic cells. Most of these responses are dependent upon 1 alpha,25(OH)2D3 interaction with a nuclear receptor protein. Structural analogues of 1 alpha,25(OH)2D3 might allow for separation of biological function, avoiding adverse calcemic effects. This report quantitates intestinal calcium absorption, bone calcium resorption, induction of intestinal and renal calcium-binding protein (CaBP), and occupancy of the intestinal and renal nuclear 1 alpha,25(OH)2D3 receptor in vitamin D-deficient chicks after a single dose of 1 alpha,25(OH)2D3, 1 alpha,25-dihydroxyvitamin-16-ene-23-yne-D3 (analogue V), or 22-[m-(dimethylhydroxymethyl)phenyl]-23,24,25,26,27- pentanor-1 alpha-hydroxy-vitamin D3 (analogue EV). The interaction of these compounds with chick intestinal nuclear 1 alpha,25(OH)2D3 receptor and chick plasma vitamin D-binding protein was determined in vitro; analogues V and EV bound 68% and 62% [1 alpha,25(OH)2D3 receptor] and 8% and 13% (vitamin D-binding protein), respectively, as well as 1 alpha,25(OH)2D3 (100%). 1 alpha,25(OH)2D3 doses (0.075-1.2 nmol) generated responses in intestinal calcium absorption, bone calcium resorption, intestinal CaBP, and renal CaBP. When analogue V (1.2-300 nmol) was administered, increases in bone calcium resorption and renal CaBP were noted. However, a significant response in intestinal calcium absorption and intestinal CaBP appeared only after a 300-nmol dose. Unoccupied nuclear 1 alpha,25(OH)2D3 receptor in the intestine and kidney was determined in vivo after doses of 1 alpha,25(OH)2D3, analogue V, or analogue EV. Doses (0.25-6.0 nmol) of 1 alpha,25(OH)2D3 and analogue EV reduced unoccupied receptor to 24% and 59% (intestine) and to 13% and 41% (kidney), respectively. Analogue V (6.0-600 nmol) decreased unoccupied receptor in the kidney. In the intestine analogue V (300-600 nmol) reduced unoccupied receptor only to 75%. These results confirm that some vitamin D analogues can generate selective biological responses and different levels of target organ receptor occupancy.

[Multicentre study of comparative efficacy of meropenem and combined regimens for empirical antibacterial therapy of severe nosocomial infections: results of clinical and pharmacoeconomic analysis].

Adequacy and effectiveness of empirical antibacterial therapy of severe nosocomial infections with meropenem vs. combined regimens of antibacterial therapy were investigated and the ratio of the cost and effectiveness of the compared regimens was evaluated. A prospective, randomized, open, comparative study of two initiative regimens of empirical antibacterial therapy of severe nosocomial infections was performed: meropenem in a daily dose of 1.5-3 g and the standard regimen with the use of betalactams and fluoroquinolones in combination with aminoglycosides and/or metronidazole. Patients with recorded diagnosis of nosocomial pneumonia (including the ventilator-associated one) or abdominal infection with the signs of severe sepsis and severity of APACHE II > 14 were enrolled. The patients were stratified into 2 groups subject to the disease severity, i.e. APACHE II 15-20 and APACHE II 21-25. One hundred thirty five out of 166 patients with recorded nosocomial infection were included into the final estimate of the therapy adequacy and effectiveness (Protocol Analysis): 62 patients were treated with meropenem and in the treatment of 73 patients the standard antibacterial therapy was used. In the group of the patients treated with meropenem there were stated significantly higher clinical effectiveness (recovery in 80.6% of the patients vs. the control of 46.6%, p < 0.01) and pathogen eradication (89.6 and 48.1% respectively, p < 0.01). The difference in the clinical and bacteriological effectiveness of meropenem and the standard therapy was more evident in the subgroups of more severe patients (APACHE > 20). With the use of meropenem the probability of recovery from nosocomial infection was significantly higher (RR 1.73-1.94, p < 0.001) vs. the control. Meropenem provided significantly higher eradication of the pathogens: P. aeruginosa (88 and 40% respectively, p = 0.007), E. coli (100 and 46.7%, p = 0.003), Acinetobacter spp. (90.9 and 40%, p = 0.02). The antibacterial therapy with the use of meropenem was assessed as adequate in 51 out of 56 patients (91.1%), that was 3 times as frequent as with the use of the standard antibacterial therapy (33.9%). The cost-effectiveness coefficient with the use of meropenem was 2.2 times lower vs. the control. Therefore, the empirical therapy of severe nosocomial infections with meropenem proved to be more adequate and from the economic viewpoint more advantageous vs. the standard combined regimens of antibacterial therapy, that was evident from significantly higher clinical and bacteriological efficacy of the treatment and decrease of the terms of the patients hospitalization in intensive care units (on the average by 5 days).

1,25-Dihydroxyvitamin D3 evokes oscillations of intracellular calcium in a pancreatic beta-cell line.

The steroid hormone 1 alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] can elicit biological responses via a nongenomic pathway that involves rapid opening of the plasma membrane Ca2+ channels. There is also evidence that 1,25-(OH)2D3 influences insulin secretion in the pancreatic beta-cell, which is primarily mediated by a rapid rise in the concentration of intracellular free Ca2+ ([Ca2+]i). We employed fluorescent digital ratiometric video imaging at the single cell level to study the effects of 1,25-(OH)2D3 on [Ca2+]i in a pancreatic beta-cell line, RINr1046-38. In RIN cells equilibrated at a steady state glucose concentration (5.5 mM), 1,25-(OH)2D3 (2-20 nM) rapidly, within 5-10 sec, increased [Ca2+]i and evoked sinusoidal [Ca2+]i oscillations with a frequency of 1.87 +/- 0.13 min-1 and an amplitude of 236 +/- 3 nM (from the initial basal level of 110 +/- 2 nM). The [Ca2+]i oscillations were acutely dependent on extracellular Ca2+, but not on extracellular glucose. Further, we investigated the mechanisms of activation by 1,25-(OH)2D3 of the Ca2+ entry pathway in the plasma membrane and analyzed the relationship between 1,25-(OH)2D3-stimulated Ca2+ entry and Ca2+ release from intracellular stores. The 1,25-(OH)2D3-evoked [Ca2+]i oscillations were mediated by nonselective Ca2+ channels, which are permeable to Mn2+ and suppressed by extracellular La3+. Blockage of voltage-dependent Ca2+ channels by nifedipine significantly decreased the amplitude of the oscillations. Depletion of intracellular Ca2+ stores with thapsigargin did not affect the 1,25-(OH)2D3-stimulated Ca2+ entry estimated by the Mn2+ entry and fura-2 fluorescence quench, which implies that the hormone directly activates nonselective Ca2+ channels. The 1,25-(OH)2D3-evoked increase in the background Ca2+ influx appears to generate [Ca2+]i oscillations by triggering Ca2+ release through the ryanodine receptor/Ca2+ release channel, but not through activation of the inositol 1,4,5-triphosphate receptor. Our findings are consistent with a role of the plasmalemmal vitamin D receptor coupled to the plasma membrane Ca2+ channels in mediating rapid effects of the hormone. We propose that the 1,25-(OH)2D3-mediated Ca2+ signaling pathway may be involved in the regulation of insulin secretion from the pancreatic beta-cell.

Vitamin D metabolism in the Damara mole-rat is altered by exposure to sunlight yet mineral metabolism is unaffected.

Vitamin D may be endogenously synthesized in the skin in the presence of sunlight or, alternatively, acquired from dietary sources. Cryptomys damarensis appear to have a naturally impoverished vitamin D status with low plasma concentrations of both 25-hydroxyvitamin D (25(OH)D; < 5 ng/ml) and 1,25-dihydroxyvitamin D (1,25(OH)2D; < 20 pg/ml). We attribute this to their underground habitat and herbivorous habits. We questioned whether these subterranean mammals could utilize sunlight-mediated pathways and therefore compared vitamin D metabolism and function when animals were (a) housed naturally (control), (b) given an oral vitamin D3 (D3) supplement (1 IU/g dry matter food eaten per day) and (c) exposed to 10 h of sunlight. Control animals exhibited a highly efficient apparent fractional absorption of both calcium (Ca) and inorganic phosphorus (Pi) (> 90%), passive mode of intestinal mineral uptake, yet tightly regulated serum ionized calcium (Ca2+). The ratio of 25(OH)D-1 alpha-hydroxylase (1-OHase) to 25(OH)D-24R-hydroxylase (24-OHase) activity in the kidney, corresponded with a state of vitamin D deficiency. Cryptomys damarensis responded to both oral D3 supplementation and sun exposure by an increase in plasma concentration of 1,25(OH)2D with a commensurate decline (P < 0.05) in 1-OHase activity, and a resulting decrease (P < 0.05) in the ratio of 1-OHase:24-OHase activity. Despite these changes, the intestinal mode of Ca uptake and plasma total Ca, Ca2+ and Pi remained unchanged with either treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin D hydroxylases and their regulation in a naturally vitamin D-deficient subterranean mammal, the naked mole rat (Heterocephalus glaber).

The vitamin D hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) is generated by a series of hydroxylation steps in the liver and kidneys. We investigated whether naturally vitamin D-deficient subterranean mammals (naked mole rats, Heterocephalus glaber) employ the same enzymatic pathways, and whether these are regulated in a similar manner to that established for other mammals. Vitamin D3-25-hydroxylase in the liver and both 25-hydroxyvitamin D3-1-hydroxylase and 25-hydroxyvitamin D3-24 hydroxylase (1-OHase and 24-OHase) in the kidney were detectable in mole rats. As expected for vitamin D-deficient mammals, the 1-OHase activity predominated over the 24-OHase. After mole rats received a supraphysiological supplement of vitamin D3, 1-OHase activity was suppressed and 24-OHase activity was enhanced. Irrespective of vitamin D status, forskolin (a protein kinase A activator) and dibutyryl cyclic AMP did not alter the activity of either 1-OHase or 24-OHase. These findings suggest that the response of renal hydroxylases to parathyroid hormone was blunted. Phorbol esters, 12-O-tetradecanoylphorbol 13-acetate (TPA) and 1-oleoyl-2-acetylglycerol (OAG) (protein kinase C activators), suppressed 1-OHase activity. 24-OHase activity was induced by TPA but not by OAG. These effects were similar to those illicited by vitamin D3 supplementation but were additive in that they increased the responses shown in vitamin D-replete mole rats. These data confirm that naturally vitamin D-deficient mole rats can convert vitamin D3 to the hormone, 1,25(OH)2D3.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium as a mediator of 1,25-dihydroxyvitamin D3-induced apoptosis.

Cellular calcium has been implicated in induction of apoptosis. We have shown that 1,25(OH)(2)D(3)-induced apoptosis is associated with a sustained increase in concentration of intracellular Ca(2+) ([Ca(2+)](i)) resulting from depletion of the endoplasmic reticulum (ER) Ca(2+) stores and activation of the voltage-insensitive Ca(2+) entry pathway [1,25-Dihydroxyvitamin D(3), intracellular Ca(2+) and apoptosis in breast cancer cells, in: A.W. Norman, R. Bouillon, M. Thomasset (Eds.), Vitamin D: Chemistry, Biology and Clinical Applications of the Steroid Hormone, University of California, Riverside, 1997, pp. 473-474; Vitamin D and intracellular calcium, in: P. Quinn, V. Kagan (Eds.), Subcellular Biochemistry: Fat-Soluble Vitamins, Plenum Press, New York, 1998, pp. 271-297; 1,25-Dihydroxyvitamin D(3) and calcium signaling, in: A.W. Norman, R. Bouillon, M. Thomasset (Eds.), Vitamin D Endocrine System: Structural, Biological, Genetic and Clinical Aspects, University of California, Riverside, 2000, pp. 715-718; 1,25-Dihydroxyvitamin D(3) triggers calcium-mediated apoptosis in breast cancer cells, in: A.W. Norman, R. Bouillon, M. Thomasset (Eds.), Vitamin D Endocrine System: Structural, Biological, Genetic and Clinical Aspects, University of California, Riverside, 2000, pp. 399-402; Endocrine 9 (1998) 321]. This study was undertaken to investigate mechanism of 1,25(OH)(2)D(3)-induced apoptosis in breast cancer cells and compare effects of the hormone on Ca(2+) and apoptosis in cancer and normal human mammary epithelial cells. The treatment of MCF-7 breast cancer cells with 1,25(OH)(2)D(3) induced a sustained increase in [Ca(2+)](i) and activated the Ca(2+)-dependent proapoptotic proteases, micro-calpain and caspase-12, as evaluated with antibodies to active (cleaved) forms of the enzymes and the calpain substrate. The selective inhibition of Ca(2+) binding sites of micro-calpain decreased apoptotic indices in the 1,25(OH)(2)D(3)-treated cells. 1,25(OH)(2)D(3) did not induce apoptosis in normal human mammary epithelial cells (HMECs), as evaluated by DNA fragmentation (TUNEL), loss of the plasma membrane asymmetry (Annexin V assay) and morphological criteria. In these cells, 1,25(OH)(2)D(3) triggered a transient Ca(2+) response, which was not accompanied by the calpain and caspase activation. HMEC, but not MCF-7 cells expressed the Ca(2+) binding protein calbindin-D(28k) and buffered Ca(2+) increases induced by a Ca(2+) ionophore ionomycin. In conclusion, we have identified the novel apoptotic pathway in breast carcinoma cells treated with 1,25(OH)(2)D(3): increase in [Ca(2+)](i) -->micro-calpain activation --> caspase-12 activation --> apoptosis. Our findings also imply that differences of Ca(2+) regulatory mechanisms in breast cancer versus normal mammary epithelial cells underlay resistance of normal cells and susceptibility of cancer cells to 1,25(OH)(2)D(3)-induced Ca(2+)-mediated apoptosis.

Bone tissue of hypokinetic rats: effects of 24,25-dihydroxycholecalciferol and varying phosphorous content in the diet.

Severe hypokinesia of rats given the diet with a ratio of Ca:P = 1:0.5-1:3 was accompanied by hypocalcemia, development of osteoporosis, and some intensification of renal calcinosis. The decrease of phosphorus consumption (Ca:P = 1:0.5-1:1) prevented a development of these changes in intact animals and increased bone mineralization in hypokinetic ones. Excessive phosphorus consumption (Ca:P = 1:3) produced hypocalcemia, hyperphosphatemia, and some osteoporotic changes in the bones of intact animals and intensified these changes with hypokinesia. Administration of 24,25-dihydroxycholecalciferol, an active metabolite of vitamin D3, at a dose of 1.25 micrograms/d prevented a development of bone disorders, thus effectively stimulating diaphyses and epiphyses mineralization and correcting hypocalcemia in hypokinetic rats. 24,25(OH)2D3 at the same dose did not intensify nephocalcinosis and produced no toxic symptoms with hypokinetic animals.

Vitamin D3 active metabolites as a countermeasure against disorders of calcium-phosphorus metabolism in hypokinetic rats.

Male Wistar rats that were experimentally hypokinetic were fed 24,25(OH)2D3 or 1,25(OH)2D3 separately or in combination to determine the effect on bone growth and on bone formation and resorption. It was shown that these parameters of bone metabolism are influenced by these metabolites of vitamin D3 by their effect on bone sensitivity to their activity and perhaps in the regulation of bone histogenesis.

[Congenital (hereditary) long QT syndrome: possible factors predisposing to development of ventricular tachyarrhythmias. Part II]. / Vrozhdennyi (nasledstvennyi) sindrom udlinennogo intervala Q-T: vozmozhnye faktory, predraspolagaiushchie k razvitiiu zheludochkovykh takhiaritmii. Chast. II.

In 3 close relatives (mother, son, mother's first cousin) with long Q-T syndrome syncopal attacks were preceded by lowering of ionized calcium in peripheral blood. This mechanism is supposed to be a trigger of ventricular tachycardia in long Q-T syndrome.

[A simple method of determining 1,25-(OH)2D (calcitriol) in blood]. / Prostoi metod opredeleniia 1,25-)OH)2D (kal'tsitriola) v krovi.

Simple and effective procedure was developed for solid-phase extraction of 1,25(OH)2D (calcitriol) from blood serum or blood plasma using mini-columns "Silica-Cart C18" which enabled to purify the hormone preparation to the state suitable for its subsequent evaluation by means of RRA and RIA. Separation of 1,25(OH)2D from 25-OHD and purification from lipophilic impurities were carried out on the single mini-column where solvents with gradually decreased polarity were used: water, methanol-water (7:3), hexane-chloroform (9:1), hexane-isopropanol (99:1), hexane-isopropanol (85:15). Concentration of 1,25(OH)2D was adequately estimated in blood serum of patients with chronic kidney insufficiency as well as in blood serum of vitamin D deficient animals.

[Metabolism of vitamin D in exogenous hypercorticism in rats]. / Obmen vitamina D pri ékzogennom giperkortitsizme u krys.

Short-term administration of hydrocortisone into rats (within 7 days) stimulated 1.25(OH)2D3 synthesis in kidney and led to accumulation of the metabolite in blood serum, small intestinal mucose and bones. After long-term administration of hydrocortisone within 28 days synthesis of 1.25(OH2D3) was decreased in kidney while the content of 24.25(OH)2D3 was was simultaneously increased. Concentration of labelled 1.25 (OH)2D3 and 24.25(OH)2D3 was distinctly decreased in small intestinal mucose and femur bones.

[Metabolism of 25-hydroxyvitamin D3 in the kidney and nuclear receptors of 1,25-dihydroxyvitamin D3 in small intestine mucosa of rats with vitamin B2 deficiency]. / Obmen 25-oksivitamina D3 v pochkakh i iadernye retseptory 1,25-dioksivitamina D3 v slizistoo obolochke tonkoi kishki u krys pri nedostatochnosti vitamina B2.

Effect of vitamin B2 deficiency on metabolism, reception and biochemical functions of vitamin D was studied in young rats. Deficiency in vitamin B2 was shown to cause a moderate hypocalcemia as well as a decrease in the active transport of calcium in small intestine and in concentration of 25-OH D in blood serum, lowered formation of 24,25 (OH)2D3 in kidney slices and decreasing content of nuclear receptors for 1,25 (OH)2D3 (fre and bound in vivo) in small intestine mucose. After administration of cholecalciferol into the animals deficient in vitamins D and B2 within 24 hrs or 6 days before death restoration of the calcium metabolism parameters was retarded as a result of less distinct stimulation of I-hydroxylase and of low activity of 24-hydroxylase 25-OH D3 in kidney as well as due to a moderate increase in content of bound receptors of 1,25 (OH)2D3 in small intestine mucose and, apparently, because of reduced production of the proteins dependent on vitamin D in the tissue (Ca2+-ATPase and alkaline phosphatase). The data obtained suggest the possible importance in rickets of vitamin B2 deficiency mediated via its influence on metabolism and reception of vitamin D.

[1,25-Dihydroxyvitamin D3 receptors in lymphocytes and T- and B-lymphocyte count in patients with glomerulonephritis]. / Retseptory 1,25-digidroksivitamina D3 v limfotsitakh i uroven' T- i B-limfotsitov u bol'nykh glomerulonefritom.

Content of receptors to hormonal form of vitamin D3, 1.25(OH)2D3, constituted 27.3 fmole/mg of protein in lymphocytes of peripheric blood of children with glomerulonephritis. In the patients concentration of total and ionized form of Ca2+ was decreased down to 2.04 mmole/L and 1.09 mmole/L, respectively, while an increase in parathormone (PTH) by 36% and a distinct decrease in 25(OH)D concentration (lower than 1.25 ng/ml) was found in blood; content of cAMP was also decreased in lymphocytes by 33%. At the same time, total content of T lymphocytes was decreased 1.5-fold in peripheric blood. Treatment with I-hydroxyvitamin D3 (1-1.5 mg daily, within 4 weeks) led to normalization of total and ionized form of Ca2+ and of 25(OH)D, but did not affect the PTH content in blood. Concentration of the receptors to 1.25(OH)2D3 was elevated up to 39.7 fmole/mg after I week of the treatment, whereas it was decreased to the initial level 24.8 fmole/mg within 4 weeks; simultaneous alteration in the cAMP content was observed in lymphocytes. Treatment with 1-(OH)D3 normalized also the T lymphocytes content in peripheric blood. The data obtained suggest that under conditions of glomerulonephritis only high content of receptors to 1.25(OH)2D3 in lymphocytes enabled to perform the cell response to the hormone effect.

[The effect of vitamin K deficiency in rats on various enzyme systems participating in energy metabolism]. / Vliianie nedostatochnosti vitamina K u krys na nekotorye fermentnye sistemy, uchastvuiushchie v énergoobespechenii.

In alimentary deficiency of vitamin K in rats, accompanied by an increase in the prothrombin time by 30%, activity of kidney creatine kinase and of blood serum alkaline phosphatase was unaltered, while the activity of alkaline phosphatase in small intestinal mucose was decreased by 20% and that of creatine kinase from skeletal muscles--by 10%. In vitamin K-deprived animals the rate of coupling between respiration and mitochondrial phosphorylation was decreased, which might be due to alteration in the NADH-dehydrogenase complex. Menadion reductase activity and cyanide-resistant respiration of mitochondria were unaltered in presence of menadion. Palmitic acid effectively activated of mitochondrial respiration in vitamin K-deprived animals (contrary to the control rats). This effect appears to occur as a result of structural alterations in mitochondria depending on vitamin K level in the organelles.

[Effect of mycotoxins aflatoxin B1 and T-2 toxin on the vitamin D3 metabolism and binding of its hormonal form 1,25-dihydroxyvitamin D3 in rats]. / Vliianie mikotoksinov--aflatoksina B1 i T-2 toksina--na obmen vitamina D3 i retseptsiiu ego gormonal'noi formy--1,25-dioksivitamina D3--u krys.

Effects of aflatoxin B1 and T-2 toxin, administered daily within 7 days at the doses of 0.7 mg/kg and 0.54 mg/kg, respectively, on metabolism of Ca and on the vitamin D hormonal system were studied in young rats kept on a ration containing normal (0.025 mg/kg) and high (0.25 mg/kg) amounts of vitamin D. Administration of the mycotoxins caused hypocalcemia, a decrease in absorption of Ca as well as in activity of alkaline phosphatase in small intestine mucose, while alterations in spongy bones (of the type of osteopetrosis) were most distinct in T-2 toxin treatment. Concentration of 25(OH)D3 in blood serum and activity of 25-hydroxylase D3 in liver tissue were decreased by 28% and 58%, respectively, after administration of T-2 toxin, and by 34% nd 33%, respectively, after treatment with aflatoxin B1. In kidney activity of I-hydroxylase 25(OH)D3 was unaltered and the activity of 24-hydroxylase tended to decrease. After treatment with the mycotoxins content of nuclear receptors of 1,25(OH)2D3 was decreased in small intestine mucose, whereas cytoplasmic receptors were increased 2.5-fold, thus indicating the distinct decrease in the receptors internalization. High doses of vitamin D caused an increase of Ca content in blood serum and of its absorption in small intestine as well as normalized Ca content in cortical bone of rats treated with T-2 toxin. At the same time, activity of 1-hydroxylase 26(OH)D3 was increased in liver tissue, while concentration of 1,25(OH)2D3 receptors was reduced in small intestine, but internalization of the hormone receptors was maintained at low level.(ABSTRACT TRUNCATED AT 250 WORDS)

[Comparative study of the effect of 1,25 dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 on calcium homeostasis and bone tissue state in rats during hypokinesia]. / Sravnitel'noe izuchenie vliianiia 1,25-dioksivitamina D3 i 24,25-dioksivitamina D3 na gomeostaz kal'tsiia i sostoianie kostnoi tkani u krys pri gipokinezii.

Preventive administration of vitamin D3 active metabolites 1.25(OH)2D3 and 24.25(OH)2D3 into growing rats, kept under conditions of long-term hard hypokinesia, normalized Ca metabolism and the state of bone tissue depending on the preparations dose and their combination. 1.25(OH)2D3 at a dose of 0.03 microgram per an animal daily augmented effectively the Ca absorption in small intestine, corrected hypocalcemia, increased slightly the bone tissue density and the Ca and P content in the tissue as well as it elevated the volume of spongiosa, width of the epiphysial growth plate (EGP) and the amount of osteoclasts. After an increase of the metabolite dose up to 0.15 microgram hypercalcemia, hyperphosphatemia, intensive resorption of bone tissue, distinct increase in the osteoclasts content and ectopic calcification were observed. Administration of 1.35(OH)2D3 and 24.25(OH)2D3 combination (0.03 microgram and 0.25 or 1.25 micrograms, respectively) or only 24.25(OH)2D3 at a dose of 1.25 micrograms caused a restoration of Ca absorption in intestine and of its level in blood as well as mineral composition, density of bone tissue, volume of primary and secondary spongiosa were normalized, while the EGP width and amount of osteoclasts remained decreased. Synergic effect of 1.25(OH)2D3 and 24.25(OH)2D3 in rats appears to depend on their various functions in regulation of Ca metabolism, in development and remodelation of bone tissue, thus indicating that these metabolites of vitamin D3 should be used simultaneously under conditions of hypokinesia for prophylactic purposes.

[Metabolism of 3H-25-oxycholecalciferol in rats with experimental fracture of the femur]. / Obmen 3H-25-oksikholekal'tsiferola u krys s éksperimental'nym perelomom bedra.

At the third day after femur fracture concentration of 3H-25-hydroxycholecalciferol [3H-25(OH)D3], intraperitoneally administered into rats within 18 hrs before killing, was increased in kidney and small intestine mucosa by 25% and 60%, respectively, as well as incorporation of the label into 1,25(OH)2D3 in blood serum and small intestine mucosa was increased by 50% and 70%, respectively, as compared with intact controls. Binding of 3H-25(OH)D3 was increased 2-3-fold in diaphyses and epiphyses of impaired bones within 3 and 10 days after the fracture. Similar, but less distinct accumulation of 3H-25(OH)D3 was observed in unimpaired femur of rats with the bone fracture. Incorporation of the label into 1,25(OH)2D3 and 24,25(OH)2D3 was increased 1.5-2-fold in epiphyses of the impaired bone as well as in epiphyses and diaphyses of intact femur of rats with the bone fracture at all the periods studied (3, 10, 28 days after the fracture).

[Effect of 24,25-dihydroxycholecalciferol on chemical composition of the rat bone tissue during hypokinesia]. / Vliianie 24,25-dioksikholekal'tsiferola na khimicheskii sostav kostnoi tkani krys pri gipokinezii.

Severe hypokinesia in rats, maintained on rations with the Ca:P ratios from 1:0,5 to 1:3, was accompanied by hypocalcemia, osteoporosis and a slight increase in kidney carcinosis. Decrease in phosphorus consumption (Ca:P = 1:0,5 - 1:1) enabled to prevent these impairments in the intact animals and led to an increase in the rate of bone tissue mineralization in hypokinesia. An excessive utilization of phosphorus (Ca:P = 1:3) caused hypocalcemia, hyperphosphatemia and a slight osteoporotic destructions in bone tissue of intact animals increasing the severity of these impairments in hypokinesia. 24,25-Dihydroxycalciferol (24,25 (OH)2D3) at a daily dose 1.25 micrograms per an animal inhibited the osteoporotic destructions, stimulating mineralization of the diaphyses and epiphyses and corrected the hypocalcemia in rats under conditions of hypokinesia. 24,25 (OH)2D3 at the dose used did not increase nephrocalcinosis as well as did not exhibit a toxic effect, estimated in hypokinetic rats by alteration in body mass.

[Effect of vitamin D3 and its metabolites 1,25-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol on callus mineralization in rats with femoral fracture]. / Vliianie vitamina D3 i ego metabolitov--1,25-dioksikholekal'tsiferola i 24,25-dioksikholekal'tsiferola--na mineralizatsiiu kostnoi mozoli u krys s perelomom bedra.

Additional administration of vitamin D3 at a physiological dose of 0.25 microgram daily into rats with femur fracture within 4 weeks did not affect the specific weight and chemical composition (content of Ca2+, P) in diaphyses of intact and impaired femurs as well as the content of Ca2+. Pi and activity of alkaline phosphatase in blood serum of the animals. At a higher dose 2.5 microgram daily vitamin D3 increased concentration of Pi in blood serum but did not alter the other parameters studied. Physiological doses of 1,25-dihydroxycholecalciferol (1.25 (OH)2D3) and 24,25-dihydroxycholecalciferol (24,25 (OH)2D3) (00.3 microgram and 0.25 microgram daily, respectively) did not affect the specific weight and composition of the impaired diaphyses, content of Ca2+ and activity of alkaline phosphatase in blood but increased slightly the Pi concentration. After a 5-fold increase in the dose of 1,25(OH)2D3 (0.15 microgram daily) specific weight and content of Ca2+ were decreased in the impaired bones with simultaneous increase in concentration of Ca2+, Pi and activity of alkaline phosphatase in blood serum. These data suggest that reparation was impaired under the conditions of acceleration of the bone tissue resorption. Increased doses of 24, 25(OH)2D3 (1.25 micrograms daily) stimulated the increase in specific weight and mineralization of the impaired bones and normalized the increased alkaline phosphatase activity in blood serum. Clinical examination of 24,25(OH)2D3 could be recommended as a drug stimulating the reparation under conditions of bone fracture.

[Mechanism of impairment of calcium metabolism caused by toxin T-2; the role of the vitamin D-dependent endocrine system]. / Mekhanizm narushenii obmena kal'tsiia pri deistvii toksina T-2; rol' éndokrinnoi sistemy vitamina D.

Functions of the vitamin D-dependent endocrine system were studied in rats deprived of the vitamin after administration of T-2 toxin. Impairments of calcium metabolism, alterations in the enzymatic activity related to vitamin D3 bioactivation and receptor binding of the hormonal form 1,25(OH)2D3 were similar both in rats deprived of vitamin D, treated with T-2 toxin within 5 days at a dose of 0.54 mg/kg and in the corresponding controls. At the same time, reduction of the calcium metabolism patterns was retarded in rats obtaining vitamin D3 simultaneously with T-2 toxin. This effect was expressed as a decrease in normalization of 25-OHD concentration in blood, absence of renal I-hydroxylase 25-OHD3 activation, inspite of the higher content of parath hormone in blood and of cAMP in kidney, while concentration of bound 1,25(OH)2D3 receptors was distinctly decreased in tissues-targets in vivo. Thus, the effects of T-2 toxin on the vitamin D-dependent endocrine system were manifested as development of the vitamin, secondary deficiency, as resistance of I-hydroxylase 25OHD3 to regulating effect of parath hormone as well as inhibition of interaction between the complexes 1,25(OH)2D3-receptor and chromatin.