Strontium induced rickets: metabolic basis

Dietary strontium inhibits both the synthesis of 1,25-dihydroxycholecalciferol and intestinal calcium absorption in vitamin D(3)-repleted chicks. 1,25-Dihydroxycholecalciferol restores calcium absorption to normal, while 25-hydroxycholecalciferol is without effect in the strontium-fed chick. It is suggested that strontium induces rickets by blocking the biosynthesis of 1,25-dihydroxycholecalciferol, the metabolically active form of vitamin D in the intestine.     

Calcium absorption and calcium-binding protein synthesis: solanum malacoxylon reverses strontium inhibition

The ingestion of diets containing high concentrations of stable strontium inhibits calcium absorption and intestinal calcium-binding protein synthesis and, as shown by others, does so by inhibiting the conversion of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol, the active form of vitamin D. The addition of the South American plant Solanum malacoxylon to strontium-containing diets counteracts the inhibitory action of dietary strontium, thereby indicating that the plant contains a factor which can mimic the action of 1,25-dihydroxycholecalciferol and representing the first such factor identified in a botanical source.     

Embryonic chick intestine in organ culture: response to vitamin D 3 and its metabolites

Embryonic chick intestine maintained in organ culture responded to vitamin D(3) and its metabolites 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol by synthesis of calcium-binding protein and enchanced calcium-45 uptake. The dihydroxy metabolite was by far the most potent inducer of the protein and also acted more rapidly than vitamin D(3) to stimulate isotope uptake. Despite its lower potency, vitamin D(3) itself was effective.     

1,25-dihydroxycholecalciferol: a potent stimulator of bone resorption in tissue culture

1,25-Dihydroxycholecalciferol (DHCC), isolated from kidney homogenates incubated with 25-hydroxycholecalciferol (HCC), stimulated the release of previously incorporated (45)45Ca from fetal rat bones in organ culture, at concentrations of 10(-10) to 10(-8)M. The dose response curves for 1,25-DHCC and 25-HCC, the parent compound, are parallel, but 1,25-DHCC is about 100 times as potent on a weight basis. Brief exposure to maximum doses of either agent leads to prolonged bone resorption.     

Vitamin D: A cholecalciferol metabolite highly active in promoting intestinal calcium transport

A major polar metabolite of cholecalciferol (vitamin D(3)) obtained from chick intestines is over four times as effective as cholecalciferol and over two times as effective as 25-hydroxycholecalciferol in stimulating intestinal calcium transport 24 hours after administration. Following a considerable lag, cholecalciferol and its 25-hydroxy derivative produce a maximum stimulation of the transport response at 24 to 48 hours. The polar intestinal metabolite greatly shortens this lag, stimulating maximum calcium transport by 9 hours. At 9 hours this metabolite is at least 13 times as active as the parent cholecalciferol and as such is a likely candidate for the biologically active form of cholecalciferol in the intestine.     

Stimulation of 24,25-dihydroxyvitamin D3 production by 1,25-dihydroxyvitamin D3

Vitamin D-deficient rats produce [(3)H]1,25-dihydroxyvitamin D(3) from [(3)H]25-hydroxyvitamin D(3) regardless of dietary content of calcium or phosphate. A daily dose of 130 picomoles of 1,25-dihydroxyvitamin D(3) for a period of 5 days reduces production of [(3)H]1,25-dihydroxyvitamin D(3) to essentially zero and stimulates production of [(3)H]24,25-dihydroxyvitamin D(3). A daily dose of 325 picomoles of 25-hydroxyvitamin D(3) has a similar but less dramatic effect. On the other hand, 650 picomoles daily of 24,25-dihydroxyvitamin D(3) given to vitamin D-deficient rats had no effect. Thus it appears that 1,25-dihydroxyvitamin D(3) is an important factor in the regulation of kidney metabolism of 25-hydroxyvitamin D(3).     

25-hydroxycholecalciferol: direct effect on calcium transport

The perfused small intestine from a vitamin D deficient rat exhibits about one-half the calcium transport of the intestine from a rat given vitamin D. These levels of calcium transport can be maintained for at least 4 hours. Addition of 2.5 micrograms of 25-hydroxycholecalciferol added to the vitamin D deficient intestine via the arterial blood perfusate induces a rise in calcium transport to +D levels within 2 hours. In contrast, 250 micrograms of vitamin D(3) given in the same manner has no effect on the calcium transport level overa 4-hour period. These data provide strong evidence that 25-hydroxycholecalci ferol represents the metabolically active form of vitamin D(3).     

25-Hydroxycholecalciferol: stimulation of bone resorption in tissue culture

25-Hydroxycholecalciferol stimulates release of previously incorporated calcium-45 from fetal rat bones in doses of 0.9 to 27 units per milliliter. This effect cannot be produced by much larger doses of vitamin D(3). Comparison of stimulation of bone resorption by 25-hydroxycholecalciferol and parathyroid hormone reveals similarities with respect to time course, dose-response slope, and inhibition by calcitonin.     

1,25-dihydroxyvitamin D-responsive element and glucocorticoid repression in the osteocalcin gene

The active hormonal form of vitamin D3, 1,25-dihydroxyvitamin D3[1,25(OH), which regulates cellular replication and function in many tissues and has a role in bone and calcium homeostasis, acts through a hormone receptor homologous with other steroid and thyroid hormone receptors. A 1,25(OH)2D3-responsive element (VDRE), which is within the promoter for osteocalcin [a bone protein induced by 1,25(OH)2D3] is unresponsive to other steroid hormones, can function in a heterologous promoter, and contains a doubly palindromic DNA sequence (TTGGTGACTCACCGGGTGAAC; -513 to -493 bp), with nucleotide sequence homology to other hormone responsive elements. The potent glucocorticoid repression of 1,25(OH)2D3 induction and of basal activity of this promoter acts through a region between -196 and +34 bp, distinct from the VDRE.     

Similarity of synthetic peptide from human tumor to parathyroid hormone in vivo and in vitro

One mechanism considered responsible for the hypercalcemia that frequently accompanies malignancy is secretion by the tumor of a circulating factor that alters calcium metabolism. The structure of a tumor-secreted peptide was recently determined and found to be partially homologous to parathyroid hormone (PTH). The amino-terminal 1-34 region of the factor was synthesized and evaluated biologically. In vivo it produced hypercalcemia, acted on bone and kidney, and stimulated 1,25-dihydroxy-vitamin D3 formation. In vitro it interacted with PTH receptors and, in some systems, was more potent than PTH. These studies support a long-standing hypothesis regarding pathogenesis of malignancy-associated hypercalcemia.     

1alpha-Hydroxyvitamin D2: a potent synthetic analog of vitamin D2

A hydroxy analog of vitamin D(2), 1alpha-hydroxyvitamin D(2), has been synthesized and tested for biological activity. This vitamin derivative is active in stimulating intestinal calcium transport and bone calcium mobilization in the rat and exhibits antirachitic activity. Its biopotency is comparable to that of the corresponding vitamin D(3) analog, 1alpha-hydroxyvitamin D(3).     

Intestinal calcium transport: stimulation by low phosphorus diets

Rats maintained on a low phosphorus diet supplemented with 25-hydroxyvitamin D(3) show high intestinal calcium transport activity as compared to rats similarly treated but fed a diet containing adequate phosphorus. This increased transport activity is correlated with an increased biosynthesis of 1,25-dihydroxyvitamin D(3), the probable metabolically active form of the vitamin in the intestine.     

沙棘叶粉对AA肉鸡生产性能和钙代谢的影响

为了检测沙棘叶粉作为一种饲料添加剂对爱拔益加(AA)肉鸡生产性能和钙代谢的作用效果,试验选择健康的1日龄AA肉仔鸡公雏240只.按体重相近的原则,随机分成4组:对照组(玉米-豆粕型基础饲粮)、基础饲粮+0.25%沙棘叶粉组、基础饲粮+0.5%沙棘叶粉组、基础饲粮+1%沙棘叶粉组.每组6个重复,每个重复10只.饲养试验共...     

Extracellular and Intracellular Calcium both Involved in the Jasmonic Acid Induced Calcium Mobilization in Arabidopsis thaliana

The objective of this experiment is to evaluate the role of intracellular and extracellular Ca2＋ and calmodulin （CAM） in jasmonic acid （JA） signaling. The laser scanning microscopy was used to detect the changes of [Ca2＋]cyt of Arabidopsis thaliana leaf cells which pretreated with different types of calcium channel blocker. Moreover, the expression of VSP, one of JA response genes, was also investigated after pretreated with the above blocker and antagonist of CaM. The results showed that extracellular and intracellular calcium both involved in the JA-induced Ca2＋ mobilization, and then Ca2＋ exerted its functions through activating the CaM or CaM related proteins. The apoplast calcium influx and the calcium release from the calcium stores are both involved in the JA-induced calcium mobilization, then the JA-induced Ca2＋ transmited the JA signal through CaM or CaM related proteins, and regulated the JA responsive genes.     

Transfer of maternal calcium to the offspring via the milk

By measuring the specific activities of milk and of maternal and filial long bones 3 months after calcium-45 had been given to the then nonpregnant mothers, it was found that the magnitude of the contribution of the maternal calcium stores to milk formation is similar to the contribution to the bone calcium of the offspring, that is, 10 to 15 percent of either milk calcium or filial calcium is maternal in origin.     

膳食中添加骨糊对大鼠钙磷吸收和骨质的影响

畜禽骨骼中含丰富的蛋白质和矿物质元素，尤其钙的含量高，钙磷比值适宜。本实验用新鲜猪长骨和肋骨，经破碎、研磨制成鲜骨糊，再经烘干、碾细、制成骨糊粉，添加到膳食中。实验动物选用Ｗｉｓｔａｒ刚断乳的雄性大白鼠２８只，按体重配对随机分成四组。实验期４周。实验表明，低钙膳食中添加骨糊，可显著增加肠钙吸收量（Ｐ＜０．０５），提高股骨灰分绝对含量（Ｐ＜０．０１）、骨矿盐含量（Ｐ＜０．０１）和骨矿盐密度（Ｐ＜０．０５）。     

维生素D对动物免疫细胞的调节作用

维生素D3能调节和控制免疫细胞的增殖和分化,产生免疫调节作用。1,25-二羟维生素D3是维生素D3的活性形式,其功能研究的进展和免疫调节机制的新认识,提示它们在畜禽免疫营养上增强动物抵抗力具有广泛的应用潜力。1,25-二羟维生素D3除了直接作用于T细胞外,还通过各种机制调节单核细胞、巨噬细胞等免疫细胞的表型和功能。该文综述了维生素D3及其活性形式1,25-二羟维生素D3的细胞免疫调节功能的新认识。     

Comment on "Obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intake"

Zhang et al. (Research Articles, 11 November 2005, p. 996) reported that obestatin, a peptide derived from the ghrelin precursor, activated the orphan G protein-coupled receptor GPR39. However, we found that I125-obestatin does not bind GPR39 and observed no effects of obestatin on GPR39-transfected cells in various functional assays (cyclic adenosine monophosphate production, calcium mobilization, and GPR39 internalization). Our results indicate that obestatin is not the cognate ligand for GPR39.     

普洱茶对大鼠钙磷吸收利用的影响*

 试验采用64只雄性SD大鼠随机分为对照组、普洱茶低剂量组、普洱茶中剂量和高剂量组,每组16只,分别饮用纯净水、0.5,2和4g/(kg BW)的普洱茶茶汤。进行8周的饲养试验,在第28d和第56d每组分别屠宰8只,测定饲料、血浆、骨骼和粪中钙、磷含量,并计算钙、磷的表观消化率,研究普洱茶对大鼠钙磷吸收利用的影响。试验结果为：第28d,中剂量组骨中钙含量显著高于对照组和低剂量组(P< 0.05),高、低剂量组骨磷的含量显著低于对照组(P< 0.05)。第56d,在血钙含量、日粮中钙的表观消化率的比较中,低、中剂量组显著低于普洱茶高剂量组和对照组 (P< 0.05);在骨钙、磷的比较中,低剂量组显著高于高剂量组和对照组(P< 0.05)。试验结果表明饮用中、低剂量普洱茶可增加日粮钙的排出,使日粮中钙的表观消化率降低,从而使日粮钙的吸收利用减少,增加骨钙的含量,饮用普洱茶不会导致骨钙流失。