不同钙离子浓度透析液对血液透析患者钙平衡及甲状旁腺素的影响

目的研究不同钙离子浓度透析液对维持性血液透析(MHD)患者透析过程中钙平衡及全段甲状旁腺激素(iPTH)的影响,为透析患者个体化选择透析液钙离子浓度提供理论依据.方法 12例血钙正常的稳定的MHD患者分别使用钙离子浓度为1.25 mmol/L(DCa1.25)、1.5mmol/L(DCa1.5)和1.75 mmol/L(DCa1.75)的透析液进行血液透析(透析液其他成分不变),每次透析4 h.检测透析前后血清总钙(tCa)、离子钙(iCa)、iPTH及透析废液的iCa和磷(P),并对血压进行监测.结果使用DCa1.25时,患者体内丢失的钙平均为5.03mmol,但透后血iCa和tCa浓度与透前相比无明显变化,iPTH透后较透前显著升高(P＜0.05).使用DCa1.5时,患者体内钙的蓄积平均为1.4 mmol,透后血iCa和tCa浓度与透前相比明显升高(P＜0.01),其中25%的患者发生透后高血钙,iPTH较透前无明显变化;使用DCa1.75时,患者体内钙的蓄积平均为3.3 mmol,透后血iCa和tCa浓度比透前明显升高(P＜0.01),其中83.3%的患者发生透后高血钙,iPTH较透前明显降低(P＜0.01).3种透析液对血磷的清除无明显差异(P＞0.05).结论对于透前血钙水平正常的患者,DCa1.75的透析液明显增加了患者的钙负荷,增加了透后高钙血症的发生.DCa1.25的透析液能够明显减轻钙负荷,但长期使用应注意监测iPTH水平.对于透前轻度低血钙或在正常值低限的患者,DCa1.5的透析液是适用的,如果发生透后高钙血症,则应改用DCa1.25的透析液.     

长期应用低钙透析对甲状旁腺激素的影响

目的：研究长期应用低钙透析液进行透析对患者甲状旁腺激素（parathyroidhormone,iPTH）的影响。方法：维持性血液透析患者16例,均使用钙浓度1.25 mmol/L的透析液透析3个月,比较血iPTH变化及透析前后的血钙磷水平的变化。结果：使用钙1.25 mmol/L的透析液3个月后,iPTH水平明显上升,透前血钙略有下降,透后血钙明显下降,血磷无明显变化。对于单次透析透后血iPTH较透前明显升高,下次透析前iPTH基本恢复,但略有上升。结论：长期应用（3个月）钙离子浓度1.25 mmol/L的透析液进行透析,会导致血iPTH的升高,但在可控制范围内。长期使用低钙透析时,应定期检查血的iPTH水平,以防发生继发性甲状旁腺机能亢进。     

不同钙浓度腹膜透析液对长期CAPD患者矿物质和骨代谢影响的分析

目的观察腹膜透析液钙离子浓度对持续性不卧床腹膜透析(CAPD)患者矿物质和骨代谢的影响。 方法回顾性分析我院腹膜透析中心行CAPD治疗2年以上的123例患者,根据腹膜透析液钙离子浓度分为低钙腹膜透析液组(LCD组,钙离子浓度为1.25 mmol/L)和标准钙腹膜透析液组(SCD组,钙离子浓度为1.75 mmol/L),观察不同钙浓度腹膜透析液对患者血清钙、磷、全段甲状旁腺激素(iPTH)、颈动脉厚度、心脏瓣膜钙化及骨痛、皮肤瘙痒等情况的影响。使用SPSS 18.0统计软件包进行数据处理。 结果2组患者治疗前人口学特征、腹膜转运特性、钙磷代谢等指标的基线水平差异无统计学意义(P>0.05)。治疗2年后,2组患者血钙浓度及达标率较治疗前均显著增高(P<0.05),SCD组血钙浓度增幅高于LCD组,但差异无统计学意义(0.26±0.31 mmol/L与0.17±0.29 mmol/L, t＝1.621,P＝0.108);2组间治疗后血清钙、磷、iPTH平均水平及其达标率、颈动脉厚度、心脏瓣膜钙化比例、骨痛及皮肤瘙痒累计发生率差异均无统计学意义(P>0.05);LCD组活性维生素D使用比例显著高于SCD组(χ² ＝6.373,P<0.05)。 结论采用低钙与标准钙腹透液治疗2年,对CAPD患者矿物质和骨代谢的影响无显著性差异。     

降低透析液钙浓度对慢性肾脏病-矿物质骨代谢异常的影响

目的探讨降低透析液钙浓度对维持性血液透析患者慢性肾脏病-矿物质骨代谢异常(CKD-MBD)各项评估指标和相关药物使用的影响,初步了解1.25 mmol/L钙浓度透析液的适用人群。方法回顾性分析四川大学华西医院血液透析中心门诊透析患者在透析液钙浓度由1.5 mmol/L调低为1.25 mmol/L后的1年中的临床资料,比较透析液钙浓度调整前后血清钙、磷、甲状旁腺素(PTH)、碱性磷酸酶等CKD-MBD评估指标的检测值和达标情况以及钙剂和骨化三醇的使用剂量。依据基线PTH值对CKD-MBD患者进行分组分析,评价低钙透析液对各组患者继发性甲状旁腺功能亢进的影响。结果共纳入281例透析患者,透析液钙浓度降低后血钙和血磷水平无明显变化(P0.05),PTH和碱性磷酸酶水平明显增高(P0.05)。1.25 mmol/L钙浓度透析液使用1年后和使用前比较,血钙和血磷的达标率差异无统计学意义(P0.05),而PTH达标率由56.1%下降至49.8%,差异有统计学意义(P0.05)。透析液钙浓度调整后患者每周的碳酸钙使用剂量无明显变化(P0.05),而骨化三醇的使用量由(1.87±1.09)μg/周明显增加为(2.62±1.26)μg/周(P0.05)。不同PTH基线值分组的患者对1.25 mmol/L钙浓度透析液的反应不同,基线PTH300 ng/L的分组在药物调控后有59.5%患者PTH值高于目标值上限,较基线情况明显增加(P0.05)。结论 1.25 mmol/L钙浓度的透析液相较于1.5 mmol/L钙浓度的透析液对血清钙和磷的水平无明显影响,但可引起PTH的升高,诱发或加重继发性甲状旁腺功能亢进和高转运性骨病;基线PTH值较低的患者使用低钙透析液后可能获益更多,为更适宜人群。     

单中心腹膜透析患者钙磷代谢不达标的影响因素分析

目的回顾性分析山西医科大学第二医院腹膜透析中心近5年腹膜透析(peritoneal dialysis,PD)患者钙磷及全段甲状旁腺素(intact parathyroid hormone,iPTH)等相关生化指标,分析矿物质及骨代谢异常产生的原因,进一步提高PD患者的生活质量和改善预后。方法选取山西医科大学第二医院2014年1月至2018年12月间进行长期维持性腹膜透析患者102例,随访3个月以上,回顾性分析患者的基线和最后一次回院随访资料。了解其钙磷代谢紊乱情况,并按血钙、血磷及iPTH水平分为达标组、不达标组,比较两组临床资料差异,探讨山西省部分地区PD患者钙磷代谢不达标的影响因素。结果 PD患者中,男女比0.79∶1,年龄(51.2±13.9)岁,基线血钙、血磷、iPTH及碱性磷酸酶(alkaline phosphatase,ALP)水平分别为(2.07±0.26)mmol/L、(1.8±0.5)mmol/L、(387.8±40.3)pg/mL、(103.9±10.3)U/L,最后一次随访时平均血钙、血磷、iPTH及ALP水平分别为(2.16±0.27)mmol/L、(2.0±0.8)mmol/L、(497.8±39.6)pg/mL、(101.4±10.0)U/L。血钙、血磷及iPTH达标率分别为37.25%、48.04%、19.61%,最后一次随访时血钙、血磷及iPTH达标率分别为48.04%、34.31%、13.73%。钙磷代谢指标控制不达标因素分析结果显示:基线血肌酐(Scr)是血钙不达标的影响因素;基线钙磷乘积是血磷不达标的影响因素;透析时间是iPTH不达标的影响因素;透析时间、基线ALP是ALP不达标的影响因素。结论山西地区PD患者钙磷代谢紊乱问题突出,血钙、磷及iPTH达标率不理想,影响钙磷代谢不达标的因素有Scr、透析时间、钙磷乘积。     

低钙透析液治疗对维持性血液透析期间高血压患者的影响

目的：观察低钙透析治疗对维持性血液透析（ MHD）期间高血压患者的影响。方法：将61例维持性血液透析期间合并高血压的患者分为两组,对照组30例,为常规钙透析液组（1.75%）；治疗组31例,为低钙透析液组（1.25%）；记录患者在透析前及透析结束并静息30 min后的血压,研究期间对透析液钙离子浓度进行监测。在研究开始前及开始后对患者透析前后血钙及血磷情况每月进行检测,观察有无严重钙磷代谢紊乱情况,研究前后检测患者透析前后甲状旁腺激素（ PTH）水平。结果：不同透析液钙离子浓度对MHD期间血压的影响：两组治疗前,其收缩压及舒张压分别比较,差异无统计学意义（P〉0.05）；经过3个月的治疗观察,治疗组与对照组治疗后收缩压比较（134±13.2 vs 150±19.5）,P〈0.05,且舒张压比较（77±15.7 vs 89±19.2）,P〈0.05,说明不同透析液钙离子浓度对MHD期间高血压具有一定的治疗作用。不同透析液钙离子浓度对钙磷及PTH水平的影响：两组治疗前,其血钙、血磷及PTH分别比较,差异无统计学意义（P〉0.05）；经过3个月的治疗观察,治疗组与对照组治疗后血钙比较（1.9±0.13 vs 1.8±0.15）,P〉0.05；血磷比较（1.92±0.89 vs 1.89±0.99）,P〉0.05；PTH比较（267±44 vs 260±53）,P〉0.05,说明不同透析液钙离子浓度对MHD期间钙磷代谢及PTH水平无明显的影响。结论：低钙透析治疗对维持性血液透析（ MHD）期间高血压具有一定的治疗作用。     

维持性血液透析患者钙磷代谢紊乱的影响因素及其与肾性贫血的相关性

目的调查我院血液透析中心患者钙磷代谢标志物血钙、血磷、全段甲状旁腺素(intact parathyroid hormone,iPTH)等指标的达标情况,探讨维持性血液透析患者钙磷代谢紊乱的影响因素及其与肾性贫血的关系,以便更好的控制钙磷代谢紊乱并管理贫血。方法研究纳入2010年1月至2015年1月在我院血液透析中心规律行血液透析(透析时间≥3个月)的终末期肾病患者作为研究对象,收集患者年龄、性别、透析时间、透析频率、残余尿量等相关资料及患者血钙、血磷、iPTH、血红蛋白(hemoglobin,Hb)等实验室检查指标,统计我院血液透析中心患者钙磷代谢标志物血钙、血磷、iPTH等各项指标的达标情况。然后分别根据年龄、透析龄、透析频率、残余尿量进行分组,比较各组间钙磷代谢指标的差异性,再分别根据血钙、血磷和iPTH进行分组,采用趋势卡方检验及方差分析比较各组间Hb达标情况。结果①本血液透析中心263例患者中,血钙达标率45.0%,血磷达标率40.1%,iPTH达标率23.7%,与透析预后与实践模式研究第4阶段(Dialysis Outcomes and Practice Pattern Study,DOPPS4)国家达标数据(56.0%、54.5%、32.1%)比较,达标率存在一定差距。②根据透析龄进行分组,透析龄≥3年组平均血钙水平显著高于透析龄3年组平均血钙水平;根据透析频率进行分组,每周2次透析组平均血钙水平显著高于每周≤2次透析组平均血钙水平,血磷水平显著低于每周≤2次透析组。根据残余尿量进行分组,有尿组(尿量≥100 rnl/24 h)钙磷乘积显著低于无尿组。根据年龄分组,年龄45岁组平均血磷水平、iPTH水平、钙磷乘积水平显著低于年龄≤45岁组。③将血钙浓度分为2.1 mmol/L、2.1~2.5 mmol/L、2.5 mmol/L三组。随着血钙增高,Hb达标(≥110 g/L)人数占比越来越大,由38.8%上升至64%,差异有统计学意义(P0.05)。将血磷浓度分为1.13 mmol/L、1.13~1.78 mmol/L、1.78 mmol/L三组,随着血磷增高,Hb达标(110 g/L)人数占比越来越大,由31%上升至53.4%,差异有统计学意义(P0.05)。将血iPTH浓度分为150 ng/L、150~300 ng/L、300 ng/L三组。随着iPTH增高,Hb达标(≥110 g/L)人数占比越来越小,由52.8%下降至36.8%,差异有统计学意义(P0.05)。结论①适当增加透析频率及有效保护残余尿量有助于控制及改善钙磷代谢紊乱。②血钙、血磷浓度上升,有利于维持性血液透析患者Hb的达标。血iPTH浓度上升,不利于维持性血液透析患者Hb的达标。     

不同钙浓度透析液治疗甲状旁腺切除术后低钙血症的探讨

目的观察血液透析患者行甲状旁腺切除术后,使用不同钙浓度透析液纠正术后低钙血症的效果。方法回顾性分析2011年10月至2014年5月我院血液透析中心行甲状旁腺切除术的13例患者,根据术后透析治疗时使用的不同钙浓度透析液,分为A组(使用钙浓度1.50 mmol/L透析液)5例,B组(使用钙浓度1.75 mmol/L透析液)8例。分别观察2组患者术后当日、术后第3、6个月透析前后的血压及透析间期的血钙、血磷、全段甲状旁腺素(intact parathyroid hormone,iPTH),比较数值之间的变化;同时统计2组患者口服钙剂的用量,并通过彩色多普勒超声心脏瓣膜评估及胸部多层螺旋电子计算机断层扫描成像(multi-slice computed tomography,MSCT)所示心脏大血管的影像学表现,比较术前及术后第6个月患者冠状动脉钙化评分分值的变化。结果比较2组单次血液透析治疗时透析前与透析结束后4 h的血钙,2组透析结束后4 h的血钙较透析前均升高,差异有统计学意义(P0.05)。同时分别比较2组透析前与术后第3、6个月时血钙变化,差异有统计学意义(P0.05)。而2组之间透析前的血磷、iPTH无统计学差异(P0.05)。通过6个月调整治疗后,血钙较术后当日明显升高(P0.05),血磷明显下降(P0.05)。术后第6个月时,B组较A组口服钙片的剂量明显减少,血压明显上升(P0.05)。同时术前及术后第6个月心脏瓣膜评估及冠状动脉钙化评分分值无明显变化(P0.05)。结论高钙透析液能更好、更快的纠正术后出现的严重低钙血症,减少维持性钙片的服用剂量,但须注意异位钙化的风险及高血压的发生。     

低钙透析液对血液透析伴继发性甲状旁腺功能减退患者的临床研究

目的：探讨应用含钙1.25mmol／L浓度透析液进行血液透析对维持性血液透析（MHD）伴相继发性甲状旁腺功能减退患者的钙磷代谢和甲状旁腺功能的影响。方法：选择MHD6个月以上、病情稳定、连续2次血iPTH〈100pg／ml的患者60例,随机分为对照组（含钙1.5mmol／L透析液）和治疗组（含钙1.25mmol／L透析液）,每组各30例,观察时间6个月。观察并记录研究前、研究后l、3、6个月等不同时期患者血iPTH、血清校正钙、磷、钙磷乘积等指标的变化以及相关不良反应。另外,选择使用含钙浓度1.5mmol／L和1.25mmol／L透析液进行MHD的患者各20例,检测单次透析前、透析结束时以及下次透析前的血清校正钙、磷和iPTH浓度。结果：（1）治疗组单次透析后血清校正钙、磷和钙磷乘积均较透析前明显下降,iPTH浓度较透前明显升高,P〈0.01;而对照组上述血钙和iPTH浓度无明显变化;（2）透析后治疗组血清校正钙和钙磷乘积较对照组明显下降,血iPTH浓度较对照组明显升高,P〈0.01;两组血磷浓度差异无统计学意义。（3）治疗组1个月后血清校正钙、磷和钙磷乘积较治疗前开始下降,3个月后进一步下降,P〈0.05,6个月后各项指标趋于稳定;iPTH水平1个月后较治疗前明显升高,并随着治疗时间的延长,逐渐升高,P〈0.01。（4）对照组治疗后1、3、6个月上述指标与治疗前比较差异无统计学意义。（5）两组透析过程中出现的不良反应差异无统计学意义。结论：对于血iPTH〈100pg／ml MHD患者应用含钙1.25mmol／L透析液进行血液透析能较好地控制其血清校正钙、磷、钙磷乘积水平,有效地改善被过度抑制的甲状旁腺功能,并且安全性良好。     

低钙透析液及盐酸米多君对血液透析患者血压的影响

目的研究低钙离子浓度1郾25mmol/L透析液(DCa1郾25),及盐酸米多君对血透患者血压的影响。方法将透前或透后高钙血症的血透患者的透析液从DCa1.5换DCa1.25,如为出现低血压则透前停服降压药;如仍低血压或原透前未服降压药者给予盐酸米多君2.5mg或5mg。观察不同钙浓度透析及加用盐酸米多君后血压和血容量变化。所有病例检测超声心动图,以及立卧位血压和持续握力试验用以反映自主神经功能。结果本组患者共21例,男9例,女12例,年龄(54.4±14.2)岁,透析龄(33.04±30.1)月。换用DCa1.25后,9(42.9%)血例压稳定,例10(47.6%)透析中出现头晕、出汗或抽搐伴随低血压;1例仅下肢抽搐;1例心前区不适。低血压组立卧位血压实验阳性者比例显著高于血压稳定组(50%比0%,P<0.05),而超滤率、白蛋白、血红蛋白、并发症、心脏收缩舒张功能及左室肥厚比例均无显著差异。低血压组的10例患者中,停服降压药仍低血压或原未服药者共例,透析前530min予盐酸米多君2.5或5mg。DCa1.25透用析时血容量较DCa1.5明显下降[(81.6±2.09)%比(86.18±2.38)%,P<0.05),盐酸米多君可提升单用DCa1.25透析时血容量[(85.96±3.10)%,P<0.05]。结论本组使用DCa1.25的患者中约50%出现低血压,与其自主神经功能低下有关。出现低血压者可停服透前降压药,无效者或     

Adult-type hypolactasia and calcium availability: decreased calcium intake or impaired calcium absorption?

Summary Adult-type hypolactasia, as mediated by a widespread genetic predisposition, not only reduces calcium intake but also calcium absorption in the presence of high amounts of lactose and may, therefore, promote osteoporosis. A lactose-reduced diet and lactose-free calcium supplements may reverse this imbalance. Introduction and hypothesis Adult-type hypolactasia (HL) defined by the LCT_(−13910) polymorphism may reduce calcium intake by reducing dairy consumption and, therefore, promote osteoporosis. This study aimed to evaluate whether lactose also decreases intestinal calcium absorption in subjects with HL and whether lactose-reduced diet and lactose-free calcium supplementation as recommended could maintain bone mineral density (BMD). Methods Based on LCT genotyping, 73 postmenopausal women with and without HL underwent a conventional H₂ breath test with a concomitant oral strontium absorption test lasting 150 minutes, which closely reflects intestinal calcium absorption. In addition, we compared bone-specific laboratory parameters, lumbar and femoral BMD, and spinal radiographs to a similar bone assessment 5 years earlier. Results LCT genotyping and functional lactose malabsorption tests were highly correlated. Dairy product consumption was reduced by 80% in HL individuals. During concomitant lactose application, mean strontium absorption was blunted by 54% in HL subjects after 150 minutes (1272 ± 629 μg/L vs. 2020 ± 1130 μg/L in lactose tolerant subjects, p = 0.001). Nevertheless, BMD in HL subjects remained stable with lactose-free calcium supplements during the observation period. Conclusion Both decreased calcium intake as well as lactose-associated impaired calcium absorption may predispose subjects with HL to osteoporosis. Lactose-free calcium supplementation may help to maintain BMD in HL subjects.     

Dose dependency of calcium absorption: a comparison of calcium carbonate and calcium citrate

Calcium supplementation is recommended as a prophylaxis against bone loss. This study was performed to determine the dose dependency of calcium absorption in an attempt to derive an optimum dose schedule. Using the well-described oral calcium load technique, we measured the calcium absorption from three different calcium doses (0.5, 1.0, and 2.0 g) of both calcium carbonate and calcium citrate administered to 21 normal subjects (4 men and 17 women, 22-60 years). Nine subjects underwent two additional loads with 0.2 g of elemental calcium as calcium carbonate and as calcium citrate. The intestinal calcium absorption from calcium carbonate and calcium citrate was estimated from the rise in urinary calcium following oral ingestion of the respective calcium salt. The increment in urinary calcium post-load, reflective of intestinal calcium absorption, rose rapidly from 0 to 0.5 g calcium loads with only slight subsequent increases from the 0.5 g to 2.0 g calcium doses. Thus, results indicate that 0.5 g of calcium is the optimum dose of either calcium salt. Moreover, the increment in urinary calcium post-load was higher from calcium citrate than from calcium carbonate at all four dosage levels. The increment in urinary calcium (during the second 2 hr) following calcium citrate load (0.5 g calcium) was 0.104 +/- 0.096 mg/dl glomerular filtrate (GF), which was higher than that of 0.091 +/- 0.068 mg/dl GF obtained from 2.0 g calcium as calcium carbonate. These results confirm the superior calcium bioavailability from calcium citrate as compared with calcium carbonate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Extra-intestinal calcium handling contributes to normal serum calcium levels when intestinal calcium absorption is suboptimal

The active form of vitamin D, 1,25(OH)₂D, is a crucial regulator of calcium homeostasis, especially through stimulation of intestinal calcium transport. Lack of intestinal vitamin D receptor (VDR) signaling does however not result in hypocalcemia, because the increased 1,25(OH)₂D levels stimulate calcium handling in extra-intestinal tissues. Systemic VDR deficiency, on the other hand, results in hypocalcemia because calcium handling is impaired not only in the intestine, but also in kidney and bone. It remains however unclear whether low intestinal VDR activity, as observed during aging, is sufficient for intestinal calcium transport and for mineral and bone homeostasis. To this end, we generated mice that expressed the Vdr exclusively in the gut, but at reduced levels. We found that ~ 15% of intestinal VDR expression greatly prevented the Vdr null phenotype in young-adult mice, including the severe hypocalcemia. Serum calcium levels were, however, in the low-normal range, which may be due to the suboptimal intestinal calcium absorption, renal calcium loss, insufficient increase in bone resorption and normal calcium incorporation in the bone matrix. In conclusion, our results indicate that low intestinal VDR levels improve intestinal calcium absorption compared to Vdr null mice, but also show that 1,25(OH)₂D-mediated fine-tuning of renal calcium reabsorption and bone mineralization and resorption is required to maintain fully normal serum calcium levels.     

Fecal calcium density: a measure of calcium compliance

We evaluated fecal calcium density (mass of calcium per g dry weight of feces) as a measure of compliance with a prescribed calcium intake regimen using 4 day fecal pools collected on a metabolic research unit from subjects ingesting measured, constant intakes. Fecal calcium density was highly correlated with intake (r = 0.897, P less than 0.001). Intake estimates based on fecal calcium density exhibited a standard error of the mean equal to 3.76 mmol calcium. Since a typical calcium supplement table contains 12.5 mmol calcium, the measurement of fecal calcium density is sensitive enough to detect regular omission of one or more pills daily. Applicability of this approach to convenience samples of feces was evaluated in 15 individuals by testing homogeneity of fecal calcium density values on up to six different 3-9 g portions (wet weight) of each volunteer's fecal sample. The within-sample coefficient of variation was 9.5% for all subsamples and 7.3% for samples from individuals with intakes above 25 mmol calcium per day. Thus feces are reasonably homogeneous in regard to calcium density. Accordingly, reasonably small fecal collections should suffice for its measurement.     

Intestinal absorption of calcium from calcium ascorbate in rats

The intestinal absorption of calcium (Ca) from Ca ascorbate (Ca-AsA) was investigated in normal rats. Each animal was perorally administered either 5 mg (low dose) or 10 mg (high dose) of Ca in 1 ml of distilled water as Ca-AsA, Ca carbonate (CaCO₃), or Ca chloride (CaCl₂), which were intrinsically labeled with ⁴⁵Ca using ⁴⁵CaCl₂. The amount of radioactivity in plasma was measured periodically up to 34 h after dosing, and pharmacokinetic parameters were calculated from the radioactivity in plasma. The time taken to reach the maximum ⁴⁵Ca level (T_max) did not differ among the three groups. The area under the plasma ⁴⁵Ca level/time curve (AUC∞) value for the Ca-AsA group was significantly higher than those for the CaCO₃ and the CaCl₂ groups. The radioactivity at T_max (C_max) for the Ca-AsA group was significantly higher than those for the CaCO₃ and the CaCl₂ groups for the low dose, and comparable with or significantly higher than those for the CaCl₂ and CaCO₃ groups for the high dose. Similar results were observed for whole-body ⁴⁵Ca retention. Radioactivity in the femur 34 h after dosing was the highest in the Ca-AsA group and the lowest in the CaCO₃ group. The rank order of solubility in water, the first fluid (pH 1.2, JP-1) of JPXIII disintegration medium, acetate buffer solution (pH 4.0), triethanolamine-malate buffer solution (pH 7.0) and ammonium chloride buffer solution (pH 10.0) at 37°C was CaCl₂ > Ca-AsA > CaCO₃. In contrast, the rank order of the solubility in the second fluid (pH 6.8, JP-2) of JPXIII disintegration medium at 37°C was Ca-AsA > CaCl₂ > CaCO₃. These results indicate that the absorbability of Ca from Ca-AsA is almost comparable with, or higher than, that from CaCl₂ and significantly higher than that from CaCO₃ because of its high degree of solubility in the intestine. Therefore, Ca-AsA would be useful as a Ca supplement with relatively high absorption from intestine. Received: March 31, 1998 / Accepted: June 16, 1998     

Epithelial calcium channel: gate-keeper of active calcium reabsorption

The epithelial calcium channel present in the apical membrane of 1,25-dihydroxyvitamin D3-responsive nephron segments represents the first member of a new family of calcium channels. This review covers the distinctive properties of this highly calcium-selective channel and highlights the implications for our understanding of the process of calcium reabsorption.     

Intestinal mitochondrial calcium uptake during adaptation to dietary calcium restriction

In order to evaluate the role of mitochondrial calcium uptake in intestinal calcium absorption, the effect of adaptation to dietary calcium deficiency on the in vitro uptake of calcium by isolated duodenal mitochondria was studied. Experiments were performed utilizing 28-day-old cockerels which had received a diet adequate in vitamin D₃ and phosphate and containing either 0.08% or 1.20% calcium. Mitochondrial⁴⁵Ca uptake from chicks deprived of dietary calcium was not significantly different from controls. These results suggest that increased calcium uptake by intestinal mitochondria is not crucial for adaptation to a low calcium diet.