Osteochondrosis in fetuses of ewes overfed calcium

Summary Ewes were fedad libitum (up to maximum of 2.5 kg/day) a complete feed containing either 1.52% calcium (High Ca) or 0.59% calcium (Normal Ca) on a dry matter basis from day 50 of pregnancy, and the fetuses were removed at 133–135 days. Thyroid C cells, identified by indirect immunofluorescence, were more numerous (P<0.001) and plasma levels of 24,25-dihydroxycholecalciferol [24,25(OH)₂D] were higher (P<0.09) in fetuses of High Ca ewes. These fetuses also had retarded cartilage differentiation in the proximal humeral epiphysis and metaphysis as well as transverse trabeculation in the epiphysis. These entities are two of the hallmarks of osteochondrosis. It was shown that feeding high dietary calcium to pregnant ewes caused osteochondrosis in their fetuses. Hypercalcitoninism and/or an adverse effect of supraphysiological levels of 24,25-dihydroxycholecalciferol may have been contributory to the skeletal abnormalities.     

Early changes in the adaptation to a low calcium diet in the chick

Summary Twelve hours after the diet of 3-week-old chicks was changed from a 1% to a 0.1% concentration of calcium (Ca), the growth rate and circulating levels of growth hormone had fallen while renal 25-hydroxecholecaiferol-24-hydroxylase had risen. The amount of⁴⁷Ca incorporated into bone from an injection given 18 h previously was lower than in the control birds. Over the following 21/2 days on the low Ca diet, the renal 1-hydroxylase activity rose and the plasma prolactin level fell, but the other parameters moved back toward the control level. It was concluded that early adjustments in hormonal and mineral metabolism counteract the acute effects of a dietary Ca shortage until longer-term adaptive changes begin to compensate for a continuing Ca deficiency. The renal hydroxylase activities were not directly influenced by the level of circulating growth hormone or prolactin.     

Effect of acute changes in plasma calcium on adrenocortical secretory rates

Increases in plasma calcium levels caused by the infusion of calcium gluconate resulted in enhanced adrenocortical secretory rates in anesthetized dogs. Hypocalcemia resulting from the infusion of EDTA had no discernible effect on adrenocortical secretory rates, and hypophysectomy abolished the rise in secretory rates noted in the hypercalcemic intact animals. The mechanisms by which calcium may effect adrenocortical secretion are discussed with respect to its effect at various sites in the hypothalamo-hypophyseal-adrenocortical system.Predoctoral trainee (PHS GM 738).     

Effect of maternal insulin deficiency on vitamin D metabolite concentrations in normoglycemic pregnant rats and their fetuses

Summary The effects on vitamin D metabolite concentrations of insulin deficiency, not accompanied by hyperglycemia, were investigated in pregnant rats and in their fetuses injected with 75 mg/kg BW streptozotocin (SZ). These concentrations were measured in maternal plasma and whole fetal body. In the insulinopenic mothers, the 25OHD concentration was found to rise compared with that of control pregnant rats (7.00±1.66 ng/ml, n=16, versus control 4.50±1.60, n=10, 0.001<P<0.01). The concentration of 1,25 (OH)₂D, which was previously found to decrease in pregnant rats that were both hypoinsulinic and hyperglycemic, was not different in our control and insulinopenic rats (107.36±38.25 pg/ml, n=11, versus control 122.90±18.20, n=8). In fetuses from our SZ-injected rats, the 24,25 (OH)₂D level diminished compared with the control level (2.12±0.70 ng/g, n=11, versus control 5.23±0.95 ng/g, n=13,P<0.001). The Ca/P ratio in fetal body also decreased (0.68 versus control 1.12). It is suggested that the placental metabolism is an important determinant of normal fetal growth.     

心脏直视手术患儿主动脉开放前低钙血症对心肌缺血再灌注损伤的影响

目的 探讨心脏直视手术患儿主动脉开放前低钙血症对心肌缺血再灌注损伤的影响.方法 选择拟在体外循环下行房缺或室缺修补术患儿50例,年龄6月～4.5岁,体重5～15 kg,根据主动脉开放前血浆离子钙浓度,将患儿分为低钙组(＜1.0 mmol/L)和常钙组(≥I.0 mmol/L),观察2组患儿心脏复跳情况.分别于CPB前、停CPB后即刻、停CPB后12 h时抽取桡动脉血1.5 ml,测定血浆离子钙浓度和动脉血气;于上述时点同时抽取中心静脉血3 ml,测定血浆肌钙蛋白I(cTnI)浓度.结果 在主动脉开放前患儿低钙血症发生率为72%,低钙组较常钙组患儿年龄小,体重轻(P＜0.05),而心脏复跳时间、室颤率、辅助循环时间、拔除气管导管时间、ICU监护时间和血浆cTnI浓度两组间差异无统计学意义(P＞0.05).结论 体外循环心脏直视手术患儿主动脉开放前低钙血症对心肌缺血再灌注损伤无影响.     

老年男性2型糖尿病患者各种钙调激素与骨密度改变的关系

目的测定老年男性2型糖尿病患者各种钙调激素及骨密度,探讨老年男性2型糖尿病患者骨质疏松的发病机理,为其防治提供理论依据。方法用双能X线吸收法测定70例老年男性2型糖尿病患者及60例年龄、体重指数相匹配的对照者的腰椎及髋部骨密度,并采用放免法测定血清骨钙索(BGP)、抗酒石酸酸性磷酸酶(TRAP)、甲状旁腺素(PTH)、降钙素(CT)、1,25(OH)2D3、25(OH)D3、尿羟脯氨酸(HOP)等,两组进行比较。结果 老年男性2型糖尿病患者较对照组骨密度显著降低。血BGP、CT、1,25(OH)2D3浓度低于对照组(P<0.05).TRAP、PTH、尿HOP显著高于对照组(P<0.05)。结论老年男性2型糖尿病患者PTH、CT、1,25(OH)2D3等钙调激素分泌及代谢失常,影响骨代谢,出现糖尿病性骨质疏松,表现为骨吸收增加,骨形成减少与缓慢,骨吸收过程大于骨形成。     

Effects of high phosphate and low calcium on the hyperplasia of normal rat parathyroid in vitro

Objective To explore the effects of high phosphate and low calcium on the secretion function and cell proliferation in normal rat parathyroid tissues. Methods The rat parathyroid tissues resected by surgical operation under dissection microscope were incubated in vitro for 5 days and were treated with high phosphate or low calcium medium on the second day and the third day after incubation. The cell apoptosis at different time points was measured by flow cytometry.The levels of intact parathyroid hormone (iPTH) in the supernatant at different time points were detected by ELISA. The mRNA levels of prepro-PTH and proliferating cell nuclear antigen (PCNA) were measured by real-time PCR, while the protein levels of PCNA after the 24-hour treatment with high phosphate or low calcium medium were measured by Western blotting. Results Flow cytometric analysis showed that the percentage of normal living cells on the first day and the second day after incubation was significantly higher than that on the third day to the fifth day after incubation in the rat parathyroid tissues (all P﹤0.05), and there was no statistical difference among that on the third day to the fifth day after incubation. There was no significant difference in cell survival rates on the first day to the fifth day after incubation (all﹥85%) under normal or high phosphate medium. There was no significant difference in the daily iPTH level on the first day to the fifth day after incubation under normal medium. Compared with normal medium, the iPTH level in the supernatant under high phosphate medium increased (P﹤0.05), and the expressions of preproPTH mRNA and PCNA in parathyroid tissues were significantly up-regulated (both P﹤0.05) after the 24-hour treatment with high phosphate medium. Compared with normal medium, the iPTH level in the supernatant under low calcium medium increased (P﹤0.05), and the expression of preproPTH mRNA in parathyroid tissues was significantly up-regulated after the 24-hour treatment with low calcium medium (P﹤0.05). Conclusions It is feasible to incubate the parathyroid issues from rats in vitro, and the best incubation time should be within 2 days. Low calcium and high phosphate stimulation could increase the synthesis and secretion of PTH, while high phosphate can also promote the cell proliferation, which is an important factor for the regulation of parathyroid function in physiological state.     

Maintenance by cortisone of the calcemic response to parathyroid extract of rats on a diet without vitamin D and low in calcium

Weanling rats raised for 21 days on a vitamin D deprived, low Ca diet (0.02%), and given chronic cortisone administration (5 mg/kg/d), maintain responsiveness to the hypercalcemic effect of endogenous and exogenous parathyroid extract (PTE). The PTE action is a bone effect that does not require the presence of the kidneys, and is not related to a higher concentration of calcium or cortisone. Maintained sensitivity of D− Ca− Cort+ rats to PTE does not appear to be the consequence of a lesser degree of D-deficiency: the whole body vitamin D pool and its chloroform-soluble fraction in these animals are not different from those of their D− Ca− PTE− unresponsive controls. Repeated PTE injections for 4 days exhaust the sensitivity to the hypercalcemic action of PTE of D− Ca− Cort+ rats. The present data seem to indicate that cortisone-treated D− Ca− rats, responsive to the bone action of PTE, are characterized by a near normal bone calcium content and Ca/P ratio, and a significant increase in the number of osteoclasts.     

Effect of bisphosphonates on the increase in bone resorption induced by a low calcium diet

This study investigates whether bisphosphonate-treated rats are still able to adapt to low calcium supply through an increase in bone resorption assessed by measuring the urinary excretion of [³H]-tetracycline from chronically prelabeled rats. First it was shown that in this model, parathyroid hormone was responsible for the increase in bone resorption on the low calcium diet. In the second part, animals were treated with the three bisphosphonates—clodronate, alendronate, and ibandronate—given in two doses. Animals receiving a dose that already strongly inhibits bone resorption were still able to respond to a low calcium diet by increasing bone resorption, showing the potency of the latter as a stimulator of bone resorption. Higher doses were, however, able to blunt this response. As soon as the treatment was discontinued, this increase in bone resorption resumed with clodronate but not with alendronate or ibandronate.     

The effect of high sodium intake on bone mineral content in rats fed a normal calcium or a low calcium diet

The effect of high sodium intake on bone mineral content of rats fed a normal (0.6% Ca) or a low (0.02% Ca) calcium diet was studied. Rats on a normal calcium diet given 1.8% sodium chloride to drink showed persistent and significant hypercalciuria and subnormal bone mineral content. Total calcium content of femur was significantly lower after 4 months (p<0.02) and 12 months (p<0.001). In rats maintained on a low calcium diet (0.02% Ca), a high sodium diet for 8 weeks caused a significant loss of calcium in bone similar to that seen in animals fed a normal calcium diet for 4 months. We conclude that high sodium intake reduces bone mineral content, especially if the diet is low in calcium.     

Studies on the role of vitamin D in early skeletal development,mineralization, and growth in rats

Summary The role of vitamin D in early skeletal development was studied by measuring serum calcium and phosphorus, osseous tissue quantity and mineralization, and endochondral bone elongation in rat fetuses and pups from vitamin D-replete and vitamin D-deficient mothers. At the 20th day of pregnancy there was a slight, yet significant, increase in the amount of osteoid on trabecular bone surfaces in fetuses from vitamin D-deficient mothers. The fetal bones otherwise appeared normal in spite of severe skeletal changes in the vitamin D-deficient mothers. After parturition, the importance of vitamin D in skeletal development becomes progressively more obvious. Serum calcium levels were slightly, yet significantly, lower in vitamin D-deficient than in vitamin D-replete pups and these levels continued to fall in the vitamin D-deficient pups through lactation and after weaning. At 3 days postpartum, there was a small, yet significant, increase in the amount of osteoid on bone surfaces of the vitamin D-deficient pups. The relative amounts of osteoid in the vitamin D-deficient pups continued to increase through lactation and after weaning when compared with vitamin D-replete pups. By the 14th day of lactation and at later periods, there were significant reductions in metaphyseal mineralized tissues in the vitamin D-deficient pups when compared with the vitamin D-replete pups. At weaning and after weaning, there were substantial increases in growth plate thickness and decreases in longitudinal bone growth in the vitamin D-deficient pups when compared with the vitamin D-replete pups. The results from this study indicate that vitamin D does not appear to play a major role in fetal skeletal development. However, after birth, vitamin D becomes progressively more important with age for normal bone development, mineralization, and endochondral growth.     

Adverse interaction of low‐calcium diet and low 25(OH)D levels on lumbar spine mineralization in late‐pubertal girls

No consensus has been reached on the serum 25‐hydroxyvitamin D [25(OH)D] levels required to ensure optimal bone health around menarche. We searched for a possible interaction of 25(OH)D levels and calcium intake on lumbar spine mineralization and on biologic features of bone metabolism in healthy late‐pubertal girls. Lumbar spine parameters (ie, area, mineral content, and density) and calcium intake were evaluated in 211 healthy white adolescent girls at pubertal stages IV–V (11 to 16.9 years), together with biologic markers of calcium and bone metabolism and with International External Quality Assessment Scheme for Vitamin D Metabolite (DEQAS)–validated serum 25(OH)D levels. A high prevalence of 25(OH)D levels ≤ 30 nmol/L (41%), ≤40 nmol/L (61%), and ≤50 nmol/L (70%) was found during winter–spring. Parathyroid hormone (PTH) levels were inversely associated with 25(OH)D levels (p = .0021). In contrast, lumbar spine mineral content and density were not associated with 25(OH)D, excepted when calcium intake was below 600 mg/day (p = .0081). Girls with such low calcium intake and 25(OH)D levels of 40 nmol/L or less (9% of the cohort) had a 0.4 to 0.7 SD lower mean areal bone mineral density Z‐score than girls with higher calcium intake and/or higher 25(OH)D status. The adverse association between lumbar spine mineralization and combined calcium deficiency–low 25(OH)D levels remained significant in the 91 girls who could be followed over 4 years after their initial evaluation. We conclude that low 25(OH)D levels (≤40 nmol/L) are observed frequently during winter–spring in late‐pubertal European girls, which may exacerbate the negative impact of calcium deficiency on lumbar spine mineralization. © 2010 American Society for Bone and Mineral Research.     

Improvement of impaired calcium and skeletal homeostasis in vitamin D receptor knockout mice by a high dose of calcitriol and maxacalcitol

Vitamin D plays a major role in mineral and skeletal homeostasis through interaction with the nuclear vitamin D receptor (VDR) of target cells. Recent reports have indicated that some cellular effects of vitamin D may occur via alternative signaling pathways, but concrete evidence for mineral homeostasis has not been shown in vivo. To investigate this issue, the actions of calcitriol (1,25D) and maxacalcitol (OCT), which were developed for treatment of uremia-induced secondary hyperparathyroidism, were analyzed in VDR knockout (VDR^−/−) mice. The VDR^−/− mice were fed a rescue diet immediately after weaning. 1,25D, OCT or a control solution was administered intraperitoneally to these mice three times a week for eight weeks. Biological markers and bone growth were measured and bone histomorphometric analysis of the calcein-labeled tibia was performed 24 h after the final administration. Significantly higher levels of serum Ca²⁺ were observed in 1,25D- and OCT-treated mice, but the serum parathyroid hormone level was unchanged by both agents. Impaired bone growth, enlarged and distorted cartilaginous growth plates, morphological abnormalities of cancellous and cortical bones; a morbid osteoid increase, lack of calcein labeling, and thinning of cortical bone, were all significantly improved by 1,25D and OCT. The significance of these effects was confirmed by bone histomorphometrical analysis. Upregulation of the calbindin D_9k mRNA expression level in the duodenum may explain these findings, since this protein is a major modulator of Ca transport in the small intestine. We conclude that 1,25D and OCT both at a high dose exert significant effects on Ca and skeletal homeostasis with the principal improvement of Ca status in VDR^−/− mice, and some of these effects may occur through an alternative vitamin D signaling pathway.     

Influence of exogenous porcine growth hormone on vitamin D metabolism and calcium and phosphorus absorption in intact pigs

The influence of growth hormone (GH) on vitamin D metabolism and calcium and phosphorus absorption in vivo is not clear. We, therefore, measured calcium and phosphorus balance, plasma 1,25-dihydroxyvitamin D (1,25(OH)₂D), and intestinal vitamin D-dependent calcium-binding protein (CaBP 9k) in intact growing pigs given exogenous GH. Six 10-week-old pigs were given two daily subcutaneous injections of 50 g porcine GH/kg body weight for 2 months; six control pigs were given vehicle. They were all fed a diet containing 1.1% Ca, 0.6% P, and 1000 IU vitamin D₃/kg. Apparent Ca and P absorption and retention were measured in a 10-day balance trial at the end of the 2 months. The plasma levels of Ca, P, 1,25(OH)₂D, IGF-I, and GH were determined, and the duodenal and jejunal mucosal CaBP 9k content was measured at slaughter. The plasma Ca and P of GH-treated pigs were unchanged, but all aspects of mineral metabolism, including the plasma 1,25(OH)₂D concentration (40%), Ca absorption and retention (70%), P absorption (33%) and retention (45%), and jejunal CaBP 9k (40%), were stimulated, in addition to an increase in the circulating IGF-I concentration.     

胰岛素抵抗在2型糖尿病时血清维生素 D3和骨密度变化中的意义

目的检测胰岛素抵抗(IR)和2型糖尿病(T2DM)大鼠的胰岛鼠抵抗情况、血清25-(OH)D3和1,25-(OH)2D3水平、腰椎和股骨骨密度(BMD),探讨IR与2型糖尿病时血清维生素D3和骨密度变化中的意义。方法 18月龄wistar大鼠30只,分为正常对照组(N组)、胰岛素抵抗组(I组)、糖尿病组(D组),正常血糖胰岛素钳夹技术(EICT)测定各组大鼠IR,葡萄糖输注速率(GIR)表示IR,放免法测定各组大鼠血25-(OH)D3和1,25-(OH)2D3水平,双能X线骨密度测量仪(DEXA)测定各组大鼠腰椎、股骨BMD。结果 D组和I组GIR相当,均显著低于N组(P0.01),I组1,25-(OH)2D3低于N组(P0.05),高于D组(P0.01),三组间25-(OH)D3无显著差异,I组腰椎、股骨BMD低于N照组,高于D组(P0.05)。结论 IR是2型糖尿病导致血清活性维生素D3降低和骨密度下降的重要病理生理基础。     

槲皮素对低钙高镁饮食大鼠血清矿量和骨代谢的改善作用

目的观察槲皮素对低钙高镁饮食大鼠血清矿量和骨代谢水平的改善作用,为骨质疏松临床预防提供参考。方法将60只清洁雄性SD成年黑色大鼠随机等分为空白对照组、模型对照组和槲皮素喂养组,每组20只。空白对照组实验过程中均正常喂养,模型对照组和槲皮素喂养组均适应性喂养2周后,进行低钙高镁(钙5 mg/L,镁60 g/L,蒸馏水溶液作为饮用水)喂养3个月,槲皮素喂养组给予低钙高镁喂养期间同时给予槲皮素(2.64 kg/d)。观察各组大鼠的日常饮食量、饮水量、体重、毛发、毛发色泽、活动等一般情况,分别于低钙高镁喂养前(实验前)和给药喂养3个月时(实验后)两个时刻点进行血清矿量(血钙、血镁、血磷)及骨代谢指标(BALP、CTX-1、BGP、t PINP)测定。结果实验期间,空白对照组、模型对照组和槲皮素喂养组大鼠的日常饮食量、饮水量、体重比较无显著差异(P0.05),但空白对照组、槲皮素喂养组实验大鼠更具活力,毛发更光润。模型对照组大鼠实验后的血钙量、血磷量、BALP均下降,血镁量、BGP、CTX1、t PINP均提升,与实验前比较差异有统计学意义(P0.05)。槲皮素喂养组大鼠实验后的血钙量、血磷量、BALP均显著高于模型对照组大鼠实验后(P0.05),槲皮素喂养组大鼠实验后的血镁量、BGP、CTX1、t PINP均显著低于模型对照组大鼠实验后(P0.05)。结论槲皮素可显著改善低钙高镁饮食大鼠血清矿量和骨代谢水平,可能在低钙高镁交互作用诱导骨质疏松症的预防中起到重要作用。     

Influence of a low calcium and phosphorus diet on the anabolic effect of human parathyroid hormone (1-38) in female rats

Parathyroid hormone (PTH) or synthetic N-terminal PTH fragments administered intermittently have been established as anabolic agents in animal and human bones. In the present study, the influence of a low calcium diet on the anabolic effect of human PTH(1-38) [hPTH(1-38)] was investigated. Forty-eight 10-week-old female Sprague-Dawley rats were randomly assigned to a diet with a low calcium content (LCa) or a diet with the recommended amount of calcium (RCa). After an adaptation period of 15 days, the rats were randomly assigned to hPTH(1-38) treatment (+LCa/+RCa) or vehicle only (-LCa/-RCa) for an additional 14 days. Total bone mineral density (BMD) values of several bones were determined using quantitative computed tomography and from ratios of ash weight to volume. Biomechanical competence of the fourth lumbar vertebrae and of the right femora was assessed. An anabolic effect could be detected in both PTH-treated groups. However, the bones of the +LCa group showed significantly lower BMD and also a diminished increase in maximal breaking force compared with those of the +RCa group. The study demonstrates that the anabolic effect of hPTH(1-38) is blunted by the LCa diet. This suggests that, during PTH treatment, dietary calcium intake is critical.