Effect of age on the conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 by kidney of rat.

The decreased absorption of calcium by the small intestine of the adult may reflect changes in vitamin D metabolism with age. The purpose of this study was to compare the capacity of young (1.5 mo of age) and adult (12 mo of age) vitamin D-deficient rats to convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D, the physiologically active form of vitamin D. Young rats responded to an oral dose of 25-hydroxyvitamin D3 with significantly increased intestinal absorption of calcium and a three-fold increase in the intestinal content of vitamin D-stimulated calcium-binding protein. Adult rats showed no significant increase in these parameters. The conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 was measured in the whole animal by administering a dose of tritiated 25-hydroxyvitamin D3 and determining the appearance of tritiated metabolites in plasma and small intestine. In the adult rat, only 2.1 +/- 0.6% of the plasma radioactivity was in the form of 1,25-dihydroxyvitamin D3 after 24 h compared with 20.8 +/- 3.0% in the young. The conversion of tritiated 25-hydroxyvitamin D3 to its products was also measured directly in isolated slices of renal cortex. 1,25-Dihydroxyvitamin D3 production by adult renal slices was found to be less than one-tenth that of slices from the young. These results indicate that there is a marked decrease in the capacity of the vitamin D-deficient adult rat to convert 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3. This is probably due to the decreased capacity of the adult kidney to 1-hydroxylate 25-hydroxyvitamin D3. These studies also demonstrate the usefulness of renal slices in measuring changes in the renal conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 in the mammal.     

Metabolism of 1,25-dihydroxycholecalciferol in the rat

Administration of 60 pmoles of 1,25-dihydroxycholecalciferol to vitamin D-deficient rats on a low calcium diet gives a maximal intestinal calcium transport response in 7 hr and a maximal bone calcium mobilization response in 12 hr. During the 48 hr after injection of radioactive 1,25-dihydroxycholecalciferol, unchanged 1,25-dihydroxycholecalciferol accounts for 71-98% of the radioactivity found in the intestine with minor amounts appearing in more polar metabolites. In the bone, for the 1st 12 hr, 1,25-dihydroxycholecalciferol is the major form (75-82%) present while at 24 hr, the amount of 1,25-dihydroxycholecalciferol decreases with a corresponding rise in the amounts of metabolites both less polar and more polar than the 1,25-dihydroxycholecalciferol. Since these metabolies are at their highest concentration when bone calcium mobilization is decreasing, they are most likely not responsible for the calcium mobilization observed during the 1st 12 hr. The appearance of water-soluble radioactivity in the kidney, plasma, liver, and muscle 24 hr after 1,25-dihydroxycholecalciferol injection has been demonstrated. The present results suggest that, although 1,25-dihydroxycholecalciferol is converted to further metabolites in the rat, it is probably the form of vitamin D responsible for initiating intestinal calcium transport and bone calcium mobilization.     

1,25-Dihydroxyvitamin D3 production by human keratinocytes. Kinetics and regulation.

Human foreskin keratinocytes in vitro metabolize 25-hydroxyvitamin D3 to a number of metabolites, including 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). This metabolite remains mostly within the cell and does not accumulate in the medium under the conditions of these experiments. With time, 1,25(OH)2D3 is catabolized, and more polar metabolites appear in both the cells and the medium. The production of 1,25(OH)2D3 has an apparent Michaelis constant (Km) for 25-hydroxyvitamin D3 of 5.4 X 10(-8) M. The levels of 1,25(OH)2D3 within the cell are increased both by increased production and decreased catabolism when parathyroid hormone(1-34) and isobutylmethylxanthine are added. Exogenously added 1,25(OH)2D3 at concentrations as low as 10(-12) M reduces endogenous 1,25(OH)2D3 production, increases 1,25(OH)2D3 catabolism, and increases 24,25-dihydroxyvitamin D3 production by an actinomycin D-sensitive process. These data indicate that the regulation of 1,25(OH)2D3 production by keratinocytes is similar to, but not identical to the regulation of 1,25(OH)2D3 by the kidney.     

Metabolism of Vitamin D3-3H in Human Subjects: Distribution in Blood, Bile, Feces, and Urine

Vitamin D(3)-(3)H has been administered intravenously to seven normal subjects, three patients with biliary fistulas, and four patients with cirrhosis. Plasma D(3)-(3)H half-times normally ranged from 20 to 30 hours. in vivo evidence that a metabolic transformation of vitamin D occurs was obtained, and a polar biologically active vitamin D metabolite was isolated from plasma.Urinary radioactivity averaged 2.4% of the administered dose for the 48-hour period after infusion, and all the excreted radioactivity represented chemically altered metabolites of vitamin D. The metabolites in urine were mainly water-soluble, with 26% in conjugated form.From 3 to 6% of the injected radioactivity was excreted in the bile of subjects with T-tube drainage and 5% in the feces of patients having no T-tube. The pattern of fecal and biliary radioactivity suggested that the passage of vitamin D and its metabolites from bile into the intestine represents an essential stage for the fecal excretion of vitamin D metabolites in man.Abnormally slow plasma disappearance of vitamin D(3)-(3)H in patients with cirrhosis was associated with a significant decrease in the quantity and rate of glucuronide metabolite excretion in the urine.     

Regulation of the metabolism of 25-hydroxyvitamin D3 in primary cultures of chick kidney cells.

A primary chick kidney cell culture is described, capable of forming 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], 24,25-dihydroxyvitamin D3 [24,25(OH)2D3], and 1,24,25-trihydroxyvitamin D3 [1,24,25(OH)3D3] over several days. The apparent Km values were 0.125 microM for the 1-hydroxylase and 2.1 microM for the 24-hydroxylase. Exogenous 1,25(OH)2D3 decreased 1-hydroxylase and increased 24-hydroxylase within 4 h. 24,25(OH)2D3 produced similar effects, but only in the absence of fetal calf serum. R and S isomers of 1,24,25(OH)3D3 were about fives times less active than 1,25(OH)2D3. Bovine parathyroid hormone stimulated the 1- and reduced the 24-hydroxylase in 6 h, but this only occurred in cultures either previously treated with 1,25(OH)2D3 and EGTA to lower Ca to 0.8 mM or in cultures grown in the presence of 25-hydroxyvitamin D3 (25(OH)D3). Under the latter condition, the sensitivity to bovine parathyroid hormone was enhanced, 0.04 U/ml producing a maximum response. Synthetic aminoterminal tetratriacontapeptide (1-34) human parathyroid hormone was equally effective. In the absence of D metabolites, estradiol for 6 h produced a dose-dependent inhibition of the 1-hydroxylase, but no change in the 24-hydroxylase. Progesterone, testosterone, and corticosterone had no significant effect. In cultures grown in the presence of 25(OH)D3 no reproducible effects were obtained with either 1 microM estradiol or 1 microM testosterone, alone or in combination, but 5 microM corticosterone decreased the 1- and increased the 24-hydroxylase. Changes in Ca and P concentrations of the medium as well as addition of ethane-l-hydroxy-1, 1-diphosphate for 48 h did not affect any of the hydroxylase activities. The modulation of the hydroxylase activities by vitamin D3 metabolites and parathyroid hormone suggests that these factors regulate the renal hydroxylase by direct actions, whereas it would appear that ethane-1-hydroxy-1,1-diphosphate, Ca, P, and steroid may exert their influence indirectly.     

活性维生素D3对大鼠早期糖尿病肾病相关炎性因子的影响

目的探讨活性维生素D3对2型糖尿病大鼠肾脏损伤的预防保护作用。方法雄性SD大鼠30只随机分为对照组、2型糖尿病组(T2DM组)、2型糖尿病活性维生素D3干预组(干预组)各10只。对照组饲以普通饲料,T2DM组及干预组饲以高脂高糖饲料喂养6周后,干预组大鼠给予活性维生素D3灌胃,T2DM组给予等量花生油灌胃,7周后检测3组24h尿蛋白水平,观察大鼠肾脏组织形态学和肾功能、血生化指标,采用免疫组织化学法检测3组肾脏转化生长因子-β1,CD68和单核细胞趋化蛋白-1表达情况。结果 T2DM组大鼠三酰甘油、血糖、24h尿蛋白、胆固醇高于对照组,尿素氮、体质量低于对照组(P<0.05);干预组24h尿蛋白、血糖、肾质量高于对照组,尿素氮低于对照组(P<0.05);干预组胆固醇、24h尿蛋白低于T2DM组,肾质量和体质量高于T2DM组(P<0.01);T2DM组单核细胞趋化蛋白-1、CD68和转化生长因子-β1阳性细胞数明显高于对照组及干预组(P<0.01)。结论活性维生素D3可通过抑制糖尿病大鼠肾脏转化生长因子-β1、CD68及单核细胞趋化蛋白-1等细胞因子表达,抑制巨噬细胞浸润,对糖尿病大鼠肾脏损伤有预防保护作用。     

Abnormal regulation of renal vitamin D catabolism by dietary phosphate in murine X-linked hypophosphatemic rickets.

Hyp mice exhibit increased renal catabolism of vitamin D metabolites by the C-24 oxidation pathway (1988. J. Clin. Invest. 81:461-465). To examine the regulatory influence of dietary phosphate on the renal vitamin D catabolic pathway in Hyp mice, we measured C-24 oxidation of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in renal mitochondria isolated from Hyp mice and normal littermates fed diets containing 0.03% (low-Pi), 1% (control-Pi), and 1.6% (high-Pi) phosphate. In normal mice the low-Pi diet led to a rise in serum 1,25(OH)2D (22.2 +/- 1.8 to 48.1 +/- 6.8 pg/ml, P less than 0.05) and no change in C-24 oxidation products (0.053 +/- 0.006 to 0.066 +/- 0.008 pmol/mg protein per min) when compared with the control diet. In Hyp mice the low-Pi diet elicited a fall in serum 1,25(OH)2D (21.9 +/- 1.2 to 8.0 +/- 0.2 pg/ml, P less than 0.05) and a dramatic increase in C-24 oxidation products (0.120 +/- 0.017 to 0.526 +/- 0.053 pmol/mg protein per min, P less than 0.05) when compared with the control diet. The high-Pi diet did not significantly alter serum levels of 1,25(OH)2D or C-24 oxidation products in normal mice. Hyp mice on the high-Pi diet experienced a rise in serum 1,25(OH)2D (21.9 +/- 1.2 to 40.4 +/- 7.3, P less than 0.05) and a fall in C-24 oxidation products (0.120 +/- 0.017 to 0.043 +/- 0.007 pmol/mg protein per min, P less than 0.05). The present results demonstrate that the defect in C-24 oxidation of 1,25(OH)2D3 in Hyp mice is exacerbated by phosphate depletion and corrected by phosphate supplementation. The data suggest that the disorder in vitamin D metabolism in the mutant strain is secondary to the perturbation in phosphate homeostasis.     

1,25（OH）2D3对大鼠肾小球系膜细胞凋亡的影响

目的探讨1,25一二羟基维生素D3[1,25(OH)2D3]对大鼠系膜细胞增殖与凋亡及其相关基因Fas表达的影响。方法体外培养的大鼠系膜细胞,分为正常对照组(0 mol/L)和不同浓度1,25(OH)2D3干预组(10-10mol/L;10-8mol/L;10-6mol/L),采用四甲基偶氮唑蓝(MTT)比色法及流式细胞仪,检测不同作用时间(24 h、48 h)下,系膜细胞增殖及凋亡情况,免疫荧光染色法观察干预24 h后,凋亡相关基因Fas的表达情况并测定各组荧光强度。结果与正常对照组相比,1,25(OH)2D3干预组,可明显抑制系膜细胞增殖,促进凋亡,并呈作用时间依赖性。同时免疫荧光染色证实干预浓度越大,系膜细胞内Fas表达增多,荧光强度增高,差异有统计学意义(P<0.01)。结论 1,25(OH)2D3干预大鼠肾小球系膜细胞,能抑制细胞增殖,促进细胞凋亡,Fas的表达增多,呈浓度和时间依赖性。     

Vitamin D metabolites in normal subjects during one year. A longitudinal study

The serum concentrations of 25-hydroxycholecalciferol (25OHD3), 25-hydroxyergocalciferol (25OHD2), 24,25-dihydroxyvitamin D (24,25(OH)2D), and 1,25-dihydroxyvitamin D (1,25(OH)2D) were measured in 10 normal subjects every 2 months for 1 year. Parallel seasonal variations were found in serum 25-hydroxycholecalciferol and 24,25-dihydroxyvitamin D reaching maximum values in June. Moreover, a highly significant correlation between changes in these two metabolites was observed (r = 0.89, P less than 0.001). On the other hand, the mean serum 1,25-dihydroxyvitamin D concentration remained constant throughout the year. Our data add further evidence to the tight regulatory mechanism of serum 1,25-dihydroxyvitamin D and the lack of regulatory mechanism of serum 24,25-dihydroxyvitamin D.     

Increased renal catabolism of 1,25-dihydroxyvitamin D3 in murine X-linked hypophosphatemic rickets.

The hypophosphatemic (Hyp) mouse, a murine homologue of human X-linked hypophosphatemic rickets, is characterized by renal defects in brush border membrane phosphate transport and vitamin D3 metabolism. The present study was undertaken to examine whether elevated renal 25-hydroxyvitamin D3-24-hydroxylase activity in Hyp mice is associated with increased degradation of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] by side chain oxidation. Metabolites of 1,25(OH)2D3 were separated by HPLC on Zorbax SIL and identified by comparison with standards authenticated by mass spectrometry. Production of 1,24,25-trihydroxyvitamin D3, 24-oxo-1,25-dihydroxyvitamin D3, and 24-oxo-1,23,25-trihydroxyvitamin D3 was twofold greater in mitochondria from mutant Hyp/Y mice than from normal +/Y littermates. Enzyme activities, estimated by the sum of the three products synthesized per milligram mitochondrial protein under initial rate conditions, were used to estimate kinetic parameters. The apparent Vmax was significantly greater for mitochondria from Hyp/Y mice than from +/Y mice (0.607 +/- 0.064 vs. 0.290 +/- 0.011 pmol/mg per protein per min, mean +/- SEM, P less than 0.001), whereas the apparent Michaelis-Menten constant (Km) was similar in both genotypes (23 +/- 2 vs. 17 +/- 5 nM). The Km for 1,25(OH)2D3 was approximately 10-fold lower than that for 25-hydroxyvitamin D3 [25(OH)D3], indicating that 1,25(OH)2D3 is perhaps the preferred substrate under physiological conditions. In both genotypes, apparent Vmax for 25(OH)D3 was fourfold greater than that for 1,25(OH)2D3, suggesting that side chain oxidation of 25(OH)D3 may operate at pharmacological concentrations of substrate. The present results demonstrate that Hyp mice exhibit increased renal catabolism of 1,25(OH)2D3 and suggest that elevated degradation of vitamin D3 hormone may contribute significantly to the clinical phenotype in this disorder.     

Effects of vitamin D3 metabolites in ovariectomized rats

The effects of two vitamin D3 metabolites, 24R,25-dihydroxyvitamin D3 and 1 alpha,25-dihydroxyvitamin D3, were investigated in ovariectomized rats. The amount of ash in the femur on a defatted dry weight basis was significantly greater in rats treated with 1 microgram/kg 24R,25-dihydroxyvitamin D3, or 0.01 or 0.1 microgram/kg 1 alpha,25-dihydroxyvitamin D3 than in the controls. The concentration of bone gla protein in serum and amounts in the femur were significantly greater in rats treated with 1 or 10 micrograms/kg 24R,25-dihydroxyvitamin D3, but not those given 1 alpha,25-dihydroxyvitamin D3 compared with the controls. These results suggest that 24R,25-dihydroxyvitamin D3 increased bone mass probably through the stimulation of bone formation.     

Effect of 1,25-dihydroxyvitamin D deficiency on the metabolic clearance rate of 1,25-dihydroxyvitamin D3: studies using pigs with vitamin D-dependent rickets type 1

We have used pigs with inherited vitamin D-dependent rickets type 1 to study the effect of 1,25-dihydroxyvitamin D deficiency on the metabolic clearance rate of 3H-1,25-dihydroxyvitamin D3 infused to steady-state levels in plasma. Plasma levels of 1,25-dihydroxyvitamin D were 24 +/- 1 (SEM) pmol/l in the hypocalcaemic, homozygous piglets and 196 +/- 27 pmol/l in their normocalcaemic, heterozygous siblings. The metabolic clearance rate of 1,25-dihydroxyvitamin D3 was the same in both normal heterozygous (0.90 +/- 0.02) and hypocalcaemic, homozygous piglets (0.90 +/- 0.01 ml-1 min-1 kg-1 metabolic body size). We conclude that a deficiency of circulating 1,25-dihydroxyvitamin D does not influence the clearance of 1,25-dihydroxyvitamin D3 from the circulation of pigs.     

A vitamin D analogue (EB1089) inhibits parathyroid hormone-related peptide production and prevents the development of malignancy-associated hypercalcemia in vivo.

We have examined the effects of 1,25 dihydroxyvitamin D3 (1,25[OH]2D3) and a low calcemic analogue EB1089 on parathyroid hormone-related peptide (PTHRP) production and on the development of hypercalcemia in Fischer rats implanted with the Leydig cell tumor H-500. Leydig cell tumors were implanted subcutaneously into male Fischer rats, which received constant infusions intraperitoneally of either 1,25(OH)2D3 (50-200 pmol/24 h), EB1089 (50-400 pmol/24 h), or vehicle for up to 4 wk. A control group of animals received similar infusions without tumor implantation. Plasma calcium, plasma levels of immunoreactive iPTHRP, and tumor PTHRP mRNA levels were determined as well as tumor size, animal body weight, and animal survival time. Non-tumor-bearing animals receiving > 50 pmol/24 h of 1,25(OH)2D3 became hypercalcemic, whereas no significant change in plasma calcium was observed in animals receiving < or = 200 pmol/24 h of EB1089. Tumor-bearing animals receiving vehicle alone or > 50 pmol/24 h of 1,25(OH)2D3 became severely hypercalcemic within 15 d. However, animals treated with low dose 1,25(OH)2D3 and all doses of EB1089 maintained near-normal or normal levels of plasma calcium for up to 4 wk. Additionally, reduced levels of tumor PTHRP mRNA and of plasma iPTHRP were observed compared with controls in both vitamin D- and EB1089-treated rats. Infusion of 50 pmol/24 h of 1,25(OH)2D3 and 200 pmol/24 h of EB1089 significantly reduced tumor volume by the end of experiment. The analogue but not 1,25(OH)2D3 substantially prolonged survival time in tumor-bearing animals with longer survival achieved at the highest dose, 400 pmol/24 h, of EB1089. These studies demonstrate that 1,25(OH)2D3 and a low calcemic vitamin D analogue are potent inhibitors of PTHRP production in vivo. Low calcemic analogues may therefore represent important alternative therapy for malignancy-associated hypercalcemia.     

Measurement of vitamin D status: background, clinical use, and methodologies

Vitamin D and its metabolites are crucial to the overall health and well-being of humans and animals, having important functions in calcium homeostasis and bone metabolism. Exposure of the skin to sunlight may provide adequate levels of vitamin D; however, there are numerous reports of vitamin D insufficiency or deficiency. 25-hydroxyvitamin D (calcidiol, 25(OH)D) is regarded as the best measurement of overall vitamin D status. 1,25-dihydroxyvitamin D (calcitriol, 1,25(OH)2D) is the most biologically active vitamin D metabolite. 25(OH)D has higher affinity for vitamin D binding protein (VDBP) than 1,25-dihydroxyvitamin D; whereas, 1,25-dihydroxyvitamin D has higher affinity for the vitamin D receptor (VDR) than 25-hydroxyvitamin D. HPLC and immunoassays allow the determination of vitamin D status, as measured by 25(OH)D, and 1,25(OH)2D. Recently it has been shown that the vitamin D requirements have been underestimated and that vitamin D2 is much less potent than vitamin D3. Future studies will determine the amount of vitamin D3 necessary for optimal health and well-being.     

Absorption, disposition and preliminary metabolic pathway of 14C-rifabutin in animals and man

14C-Rifabutin was given orally to rats, rabbits and monkeys at a dose of 25 mg/kg and to healthy volunteers at a dose of 270 mg. Radioactivity was eliminated by both the renal and faecal routes in all species, with a predominance of the renal route in man and monkeys (50.19% and 46.73% of the dose, respectively, in urine at 96 h), whereas in rats and rabbits a slight predominance of faecal excretion was observed (48.09% and 45.01% of the dose, respectively, at 96 h in faeces; 42.22% and 36.37% in urine). Radioactivity as expired 14CO2 was detected in the rat and accounted for less than 0.5% of the dose within 96 h. The drug was rapidly absorbed and peak plasma radioactivity levels were reached from 1 to 4 h after dosing. Rifabutin was the predominant compound circulating in plasma at the first sampling times, but significant levels of 31-OH rifabutin were detected up to 8-24 h in all species studied. 25-O-deacetyl rifabutin was detected only in rat and man. Polar metabolites were also present, particularly at the later sampling times. The urinary metabolism was studied by radio-HPLC. Rifabutin accounted for 8.5% and 4.6% of the dose in 0-24 h urine of rats and man respectively, whereas in rabbit and monkey urine only traces of this compound were detected. The main known metabolite in all animal species was 31-OH rifabutin; 25-O-deacetyl rifabutin was detected only in rat and man. The remaining urinary radioactivity was mainly due to polar compounds.     

A simplified assay for dihydroxylated vitamin D metabolites in human serum: application to hyper- and hypovitaminosis D

We describe a simplified assay for 24,25-and 1.25-dihydroxyvitamin D in human serum. It involves two preparative steps, and normal chick intestine is used in preparing cytosol-binding protein. Our results for 24,25-dihydroxyvitamin D include a reference interval of 2.9--16 nmol/L (1.2--6.7 microgram/L), a mean of 6.7 nmol/L (2.8 microgram/L), an intra-assay CV of 11%, and an interassay CV of 22%. For 1,25-dihydroxyvitamin D, these data were 29--168 pmol/L (12--70 ng/L), 86 pmol/L (36 ng/L), 12%, and 22%, respectively. In hypoparathyroid patients with vitamin D intoxication, mean concentrations of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D in serum were significantly above normal; the 1,25-dihydroxyvitamin D concentrations were significantly below normal. Patients with malabsorption and/or post-gastrectomy states had significantly subnormal values for both 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D in serum, and there was a significantly negative correlation between each of these biochemical values and the severity of osteomalacia. We also discuss cost effectiveness of assaying vitamin D metabolites in human serum.     

中药补肾活骨方对去势骨质疏松大鼠骨代谢的影响(英文)

背景:中药补肾活骨方可有效防治骨质疏松症,但其具体的药理学机制仍不是很清楚。25-羟基维生素D3和1,25-二羟基维生素D3是调节骨吸收与骨形成的重要的偶联因子。目的:观察补肾中药对去势骨质疏松大鼠骨密度、骨生物力学、血清及肝肾组织中25-羟基维生素D3和1,25-二羟基维生素D3水平的影响。方法:健康雌性SD大鼠108只随机等分为假手术组、模型组和治疗组。后2组摘除双侧卵巢,导致雌激素缺失,从而诱导骨质疏松症模型。治疗组大鼠造模后以中药补肾活骨方2mL灌胃,2次/d。结果与结论:与模型组相比,治疗组股骨头骨密度明显提高(P<0.05),最大应力和最大负荷指数明显增强(P<0.05),血液、肝脏和肾脏组织中25-羟基维生素D3和1,25二羟基维生素D3水平明显提高(P<0.05);且接近于假手术组(P<0.05)。提示补肾中药在雌激素缺失早期即可在分子水平上调节25-羟基维生素D3和1,25-二羟基维生素D3的表达水平,激活骨代谢提高骨密度增强骨质量达到预防骨质疏松的作用。     

Biological activity of the C-1, C-3, C-25, beta-D-glucopyranosides of 1,25-dihydroxyvitamin D3

We have shown previously that the 3-beta-D-glucopyranosides of vitamin D3, 1 alpha-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3 are biologically active in vivo. In order to determine whether the presence of the beta-D-glucopyranoside moiety linked to either the C-3, the C-25 or the C-1 hydroxyl function of the molecule affected the biological activity of the conjugates 1, 2, or 3 derived from 1,25-dihydroxyvitamin D3, we administered increasing amounts of compounds to vitamin D-deficient rats maintained on a low calcium diet. The aglycone, 1,25-dihydroxyvitamin D3 (4), also was administered to another group of such animals. When administered i.v., all three beta-D-glucopyranosides increased intestinal calcium transport in doses as low as 50 pmol/rat. A dose of approximately 500 pmol/rat was required to increase bone calcium mobilization in these same animals. The three glucosides were found to be equally active in both biological responses. A dose of only 5 pmol of 1,25-dihydroxyvitamin D3 (4) increased both intestinal calcium transport and bone calcium mobilization. We also performed similar experiments after the p.o. administration of these compounds to vitamin D-deficient rats maintained on a low calcium diet. The glucopyranosides 1, 2 and 3 were able to increase calcium transport in the intestine, as well as mobilize bone calcium at doses of between 500 and 5000 pmol/rat. Once again, the compounds were equipotent, but were less active than 1,25-dihydroxyvitamin D3 (4). After the i.v. or p.o. doses of the glucosides, plasma concentrations of 1,25-dihydroxyvitamin D3 increased in a dose-dependent manner. We conclude that: The C-3, C-25 and C-1 beta-D-glucopyranosides of 1,25-dihydroxyvitamin D3 are biologically active and equipotent in vivo, most likely as a result of hydrolysis to the free aglycone and they are less active than the aglycone in this respect.     

Disposition of [14C]aztreonam in rats, dogs, and monkeys

[14C]aztreonam was administered as single 25-mg/kg doses to dogs (intravenously and subcutaneously) and monkeys (intramuscularly and intravenously) and as single 50-mg/kg doses (intramuscularly and intravenously) to rats. In rats and dogs, radioactive moieties were excreted primarily in urine; in monkeys, they were excreted about equally in urine and feces. Unchanged aztreonam accounted for 77 to 86% of the radioactivity excreted in the urine of rats, dogs, and monkeys; SQ 26,992, the metabolite resulting from hydrolysis of the monobactam ring, accounted for 10 to 15%; and minor, unidentified metabolites accounted for the remainder. In rats with cannulated bile ducts, about 15% of an intramuscular dose was excreted in bile in 24 h; the bile contained a greater percentage of metabolites than that found in urine. In dogs, the apparent elimination half-life of aztreonam in serum was 0.7 h after intravenous administration. Aztreonam and SQ 26,992 accounted for most of the radioactivity in the sera of dogs and monkeys. Serum protein binding of aztreonam and its metabolites ranged from 28 to 35% in dogs and from 49 to 59% in monkeys. In the three species studied, aztreonam was most extensively metabolized in monkeys; SQ 26,992 and other minor metabolites from monkey urine were tested and found to be devoid of any significant antimicrobial activity.     

Vitamin D metabolites in diabetic patients: decreased serum concentration of 24,25-dihydroxyvitamin D

In order to elucidate if changes in vitamin D metabolism play a role for diabetic bone loss, the serum concentrations of the major vitamin D metabolites were studied in 26 adult male ambulatory insulin-treated diabetics, selected to have normal renal function and a duration of diabetes below 11 years. The patients were studied during usual metabolic control and exhibited wide ranges of hyperglycaemia and glycosuria. The serum concentrations of the major metabolites of vitamin D, 25-hydroxyvitamin D(2 + 3) (25OHD), 24,25-dihydroxyvitamin D(2 + 3) (24,25(OH)2D), and 1,25-dihydroxyvitamin D(2 + 3) (1,25(OH)2D), were measured in diabetics, and in age and sex matched controls. The diabetics had slightly decreased serum levels of 25OHD (42.0 nmol/l versus 55.5 nmol/l in normals, P less than 0.05), markedly decreased serum levels of 24,25(OH)2D (2.98 nmol/l versus 5.91 nmol/l, P less than 0.01), but serum levels of 1,25(OH)2D were virtually normal (64.2 pmol/l versus 68.3 pmol/l, ns). The close correlation between serum concentrations of 25OHD and 24,25(OH)2D observed in the normal subjects, was absent in the diabetics. There were no correlations between the serum levels of any of the vitamin D metabolites and the measured indices of glucose and calcium metabolism. It is concluded that insulin-dependent diabetic patients demonstrate definite alterations in serum levels of vitamin D metabolites, the significance of which remains unknown at present.