同位素稀释技术比较六种不同钙剂的生物利用度

目的测定和比较6种不同的有机和无机钙剂的真正吸收率和生物利用度。方法采用同位素稀释技术。在2w的代谢研究中,60只生长期雄性SD大鼠,肌肉注射45Ca后,分为6组,每组10只,分别饲喂含柠檬酸钙、乳酸钙、醋酸钙、牡蛎壳粉、蛋壳粉和β-磷酸三钙的人工半合成饲料。6种饲料中含钙、磷、镁的量均相同,分别为2.8,5.3和0.65g/kg。结果柠檬酸钙、乳酸钙和醋酸钙等有机形式钙的真正吸收率和生物利用度（真正吸收率分别为98.8,98.3和98.6%;生物利用度分别为96.8,96.0和96.8%）略高于生物碳酸钙类的牡蛎壳和蛋壳（真正吸收率分别为97.7和96.3%;生物利用度分别为95.3和93.8%）以及无机类的β-磷酸三钙（94.9和92.0%）。然而,从实际应用角度衡量,所观察的6种钙剂均显示很高的吸收率和生物利用度。结论可以认为,膳食钙的化学形式并不是影响钙生物利用度的主要因素。     

三磷酸钠,锌,铁对草酸钙结石生长的抑制作用

通过对在动物膀胱草酸钙结石模型上利用同位素示踪技术观察三聚磷酸钠、锌、铁对草酸钙结石生长的影响及血尿有关生化物质、电解质水平变化，探讨三种物质对尿石影响的机理。结果表明：三聚磷酸钠能明显抑制结石生长，锌能轻度抑制结石生长，铁对结石生长无明显影响，本文还讨论了同位素示踪技术在尿石研究中的应用。     

脓毒症时单核细胞钙动力学的改变

本研究旨在评价临床脓毒症和实验性内毒素血症时单核细胞的钙移动。取15例外科脓 毒症患者的全血标本,同时取血清标本测定总的钙浓度;20名健康志愿者为对照组。从全血中分离单核细胞,得到淋巴细胞含量>90％的单核细胞悬液,细胞密度为3×10~6/ml。细胞活力测定应用Propidium碘化物掺入法,吸收率应     

电化学法研究钙制剂的吸收率

本文用电化学方法研究了钙制剂的吸收率。实验结果表明，活性钙具有出色的离子化百分率，其活性远远高于其它钙制剂。不同工艺生产的活性钙，其活性基本相同。和传统的“代谢法”相比，本方法不仅具有快速、准确等特点，而且不必通过人体或动物实验就可以得到满意的结果。     

钙的吸收率不同于钙的吸收利用率

钙的吸收率不同于钙的吸收利用率张晓春有些厂家在宣传钙制剂产品中谈及吸收率高（即吸收度），以此来介绍本产品的质量、疗效。然而在众多的钙产品中，有的厂家标示出吸收利用率，有的厂家却标示吸收率，对于广大消费者来说可能难以理解，误认为是吸收利用率与吸收率是意...     

复合L-氨基酸螯合钙对大鼠骨密度增加的影响

研究复合L-氨基酸螯合钙对SD大鼠骨密度的影响.将SD大鼠随机分成6组,分别喂养复合L-氨基酸螯合钙,"乐力"氨基酸螯合钙和低钙饲料,通过测量相应饲料喂养大鼠身长、体重、钙表现吸收率,股骨长度、质量、骨密度和股钙含量等指标,观察复合L-氨基酸螯合钙对SD大鼠骨密度的影响.结果表明:2种剂量的复合L-氨基酸螯合钙和"乐力"氨基酸螯合钙对大鼠的身长和体重、股骨质量、骨密度、钙含量和钙表观吸收率显著高于低钙饲料组﹙P＜0.01﹚,两种剂量水平的氨基酸螯合钙对大鼠骨密度、股骨钙含量和钙表观吸收率差异显著﹙P＜0.01﹚,复合L-氨基酸螯合钙具有增加大鼠骨密度的功能.     

~(15)N-甘氨酸、~(13)C-棕榈酸体内示踪在肠功能监测中的应用

研究应用稳定同位素~（１５）Ｎ－甘氨酸和~（１３）Ｃ－棕榈酸示踪测定全小肠切除术后患儿的肠吸收功能。方法：以 一例全小肠切除术后患儿作自身对照,两名健康儿童作正常对照,定期用~１５Ｎ－甘氨酸示踪试验和~１３Ｃ－棕榈酸呼气 试验来检测患儿残留消化道对氨基酸和脂肪酸的代偿吸收功能。结果：患儿在术后１５月及２４月对氨基酸的相对 吸收率分别为５０％和５２％,吸收高峰时间均在２．５～３．５ｈ。对脂肪酸的相对吸收率则分别为５７％和７５％,吸收高峰 时间在３．５～４．５ｈ。结论：用稳定同位素法测定肠吸收功能不仅安全、灵敏、特异性好,而且还反映肠吸收高峰时 间。根据本研究结果推断,结肠可能代偿吸收营养要素。     

绝经前后钙代谢变化的动态研究

为研究绝经前后正常钙代谢的动态变化,作者在1977～1985年间,对1930年出生的19名绝经前妇女。每年采集空腹血液和尿液标本一次,测定血清钙、磷、肌酐、碱性磷酸酶、甲状旁腺素(iPTH)、降钙素(iCT),以及尿钙、磷、肌酐,并计算出尿钙/肌酐比值和肾小管时滤过磷的重吸收率(TmPO_4/GF)。     

脱钙骨基质在鼻整形手术中的临床应用进展

脱钙骨基质为异体骨经脱脂、脱水、脱钙、冻干等处理后所得,是具备低抗原性及诱导新骨形成能力的同种异体移植物。脱钙骨基质在骨科及颌面部整形中已获得成熟应用,但在鼻整形中的应用尚有限。现简述脱钙骨基质的作用机制,并着重探讨用于鼻整形时的手术并发症与吸收率。     

影响青少年钙代谢因素的研究

目的通过代谢平衡实验探讨青少年的钙代谢特点及其影响因素,为制定钙膳食参考摄入量提供参考。方法从320名参加1年补钙实验的4组12～17岁的少年中,每组随机抽取男、女生各10人,共80人。用代谢平衡实验收集研究对象试验期内摄入的食物、排出的粪便和尿液样品,用电感耦合等离子体发射光谱法测定其钙含量。用聚合酶链反应-限制性片段长度多态性检测研究对象维生素D受体基因BsmⅠ和FokⅠ、雌激素受体基因PvuⅡ和XbaⅠ多态性。结果性别、钙摄入量、青春发育水平是主要影响青春期少年钙吸收的因素(R2=0.508)。男生和女生的钙摄入量差异无显著性,男生的钙表观吸收率和钙储留量(68.7%、479.7mg.d-1)显著高于女生(46.4%、203.7mg.d-1)。男生出现首次遗精后1年内,钙表观吸收率快速上升,1年后钙表观吸收率逐渐下降;女生出现月经初潮后2年内,钙表观吸收率快速下降,2年后趋于稳定。青春期少年钙储留量主要受性别、钙摄入量和年龄的影响(R2=0.745)。随着年龄的增长,钙储留量下降。维生素D受体基因和雌激素受体基因多态性对青春期少年的钙代谢没有显著影响。结论性别、钙摄入量、年龄和青春期发育水平是青少年钙代谢的重要影响因素,在制定青春期少年膳食钙DRIs时,需要考虑这些因素对青少年钙代谢的影响。     

Simple isotopic method using oral stable or radioactive tracers for estimating fractional calcium absorption in adult women

Summary  

We extended a simple oral method for estimating fractional calcium absorption determined by double isotopic methods using radioactive or stable isotope across wide age of adult women. Fractional calcium absorption can be estimated by using either a radioactive or stable oral isotope across the entire age spectrum of adult women.     

Malabsorption of calcium and phosphate in chronic renal failure: 32P and 45Ca studies in dialysis patients

A modified double-isotope method was used to determine the absorption of calcium and phosphate in patients with chronic renal failure. Eight hemodialysis patients and six healthy control subjects received an intravenous dose of 45calcium and 32phosphate and an oral tracer dose of 45Ca and 32P was administered two weeks later. Timed plasma samples were obtained on each occasion to determine fractional absorption rates and cumulative absorption of either tracer from both tracer sets with deconvolution analysis. Stool collections were analyzed. Calcium absorption in normal subjects peaked at 12% over fifteen minutes at one hour and declined rapidly thereafter. Absorption was essentially complete at four hours and cumulative absorption at this time was 72 +/- 6%. The pattern of phosphate absorption was similar and cumulative absorption at 4 hours was 80 +/- 3%. Calcium absorption in dialysis patients was significantly impaired with a flattened profile, a maximal 15-min absorption rate of 2% and cumulative 4-h absorption of 20 +/- 2%. Phosphate absorption in dialysis patients was also impaired to a comparable degree with a maximal rate of 3.6% and a more delayed cumulative total of 35 +/- 5%. Stool data showed good agreement with deconvolution analysis in volunteers but always overestimated absorption in patients. Sequential double isotope analysis provided a simple and convenient method for the concurrent estimation of calcium and phosphate absorption in humans.     

Lactulose stimulates calcium absorption in postmenopausal women.

Animal studies have indicated that calcium absorption is increased by lactulose, a synthetic disaccharide. Therefore, the influence of lactulose on calcium absorption was measured in postmenopausal women who may benefit from the possible enhancing effect of lactulose on calcium absorption. Twelve postmenopausal women drank 100 ml of water containing 5 or 10 g of lactulose or a reference substance at breakfast for 9 days. The three treatments were given according to a randomized, double-blind, cross-over design, separated by two 19-day wash-out periods. On the 8th day of each treatment period, 44Ca dissolved in orange juice was drunk immediately after the solution with the study substance and just before a standard breakfast with 162 mg of carrier calcium. Within half an hour, 48Ca was given intravenously. Based on isotope ratios measured in urine collected before and until 36 h after isotope administration, true fractional calcium absorption was calculated. Calcium absorption during the treatments with the reference substance, 5 g and 10 g of lactulose was (mean +/- SD) 27.7 +/- 7.7, 30.0 +/- 7.6, and 32.2 +/- 7.0, respectively. A significant difference in calcium absorption was found between the highest dose of lactulose and the reference treatment (p < 0.01). A significant linear trend was found between the dose of lactulose and its positive effect on calcium absorption. In conclusion, in postmenopausal women a 9-day consumption of lactulose increases calcium absorption in a dose-response way. More research is warranted to explore how lactulose stimulates calcium absorption and whether it is able to improve calcium balance and/or to attenuate the rate of aging bone loss.     

The efficiency of intestinal calcium absorption is increased in late pregnancy but not in established lactation

Summary The fractional absorption of calcium (FA-Ca) was measured using a dual non-radioactive Ca isotope technique in 26 control women, 49 women in the last triimester (36 weeks) of pregnancy and 31 of these women in established (20 weeks) lactation. The ratio of the two non-radioactive Ca isotopes was measured, by high precision thermal ionisation mass spectrometry, in urine 12–24 hours after administration and was used to calculate Fa-Ca. This is the first study to clearly show that FA-Ca is significantly elevated in late pregnancy but not in established lactation, when compared with control women.     

Isotopic exchange of ingested calcium between labeled sources. Evidence that ingested calcium does not form a common absorptive pool

Summary We studied the extent of salt dissociation during absorption of calcium from sources of differing absorbability by measuring fractional absorption from loads in the range of 200–300 mg in healthy adult women. Sources were labeled both intrinsically and extrinsically with⁴⁵Ca and⁴⁷Ca, respectively, and were fed alone and in combination with one another. We first confirmed our previous observation of superior absorbability of calcium oxalate over spinach calcium in a randomized cross-over design in 20 women. Spinach calcium exhibited only half the absorbability of the same load of calcium presented as the oxalate. Then, in 14 women fed spinach with both an intrinsic and an extrinsic label, apparent absorption of the extrinsic label averaged 0.130±0.041 and of the intrinsic label, 0.029±0.023. Thus, the extrinsic tag was partially, but not completely, bound by the spinach. In the same 14 women, milk absorption averaged 0.331±0.092 when ingested alone. However, when coingested with spinach, apparent milk calcium absorption fell to 0.267±0.079 and apparent spinach calcium absorption rose to 0.111±0.039. Thus, there was significant but incomplete label exchange between the two sources, indicating that at least some of the calcium from both sources enters a common preabsorptive, ionic pool. By contrast, we had previously shown no tracer exchange when labeled oxalate was co-fed with labeled milk. We conclude that (1) the presence of calcium as the oxalate in spinach is not a sufficient explanation for the poor absorbability of spinach calcium; and (2) oxalate calcium and spinach calcium are absorbed by different mechanisms, one involving a common preabsorptive pool and the other not. We suggest that oxalate calcium absorption is by passive diffusion of the intact complex and spinach calcium absorption by active transport of the free cation.     

Tracer clearance studies in hydrocephalus: A critique

Summary Quantitative isotope ventriculography (QIV) has been suggested as a method for diagnosing hydrocephalus and predicting the results of CSF shunt insertion. However, the physiological significance of this and other tracer clearance studies is questionable. Using a simplified mathematical model for tracer clearance following ventricular injection, a series of isotope retention curves were generated by an IBM 360-40 computer.The author shows that the tracer clearance from the CSF is just as dependent on the volume of the CSF compartment as it is on the rate of CSF absorption. This means, for example, that doubling the CSF volume without diminishing absorption (cerebral atrophy) yields the same results as halving the absorption rate in a patient with normal CSF volume (early hydrocephalus).In order for tracer clearance studies to measure CSF absorption, to determine the presence of hydrocephalus, and to predict the results of shunting, an accurate measure of CSF volume must be obtained.     

Time course of calcium absorption in humans: Evidence for a colonic component

Summary We examined the time course of calcium absorption (CaAbs) in 155 studies, using a double isotope technique. The subjects were 118 healthy peri-menopausal women (mean age 53.3 years), studied as impatients under metabolic balance conditions. We measured the ratio of radiolabeled calcium (oral:IV) in serum and urine for 144 hours after the oral dose, and generated a composite CaAbs curve for all 155 studies using normalized data. Although CaAbs was 80.9% complete at 3 hours, it was still only 95.8% complete at 7 hours; the remaining 4.2% was absorbed in a slower late component, and did not reach completion until about 26 hours. The rapid initial component probably represents mainly small intestinal absorption and the late component, colonic. At the dietary intakes of our subjects, we estimate the size of the late component at about 6.8 mg/day. For fully accurate measurements of CaAbs, it is necessary to allow for this small late component.     

Absorption of Calcium as the Carbonate and Citrate Salts, with Some Observations on Method

Calcium supplement use has increased and there is confusion about the relative absorbability of various sources. Absorbability of calcium from the carbonate and citrate salts was compared at 300 mg and 1000 mg calcium loads, ingested as part of a light breakfast meal. Absorption was measured at the high load both by tracer appearance in serum and by the absorptive increment in urinary calcium, and at the low load by the tracer method only. Subjects were 37 healthy adult men and women, studied as outpatients, and each tested on both salts at the same load. Mean tracer absorption (± SD) for both salts combined was 36.0% at the 300 mg load and 28.4% at the 1000 mg load. In both experiments the observed mean difference in absorption between salts was very small. By the tracer method the within-subject difference (carbonate less citrate) was +3.3%± 1.2% of the ingested dose (mean ± SEM; P <0.05) at the high load, and at the low load, 3.6%± 2.7% (NS). Combining the two experiments yielded zero difference between sources. By the urinary calcium increment method, the mean difference between salts at the 1000 mg load was 1.8 ± 4.1 mg (NS). Side-by-side comparisons of the two methods revealed that the tracer method was 3 times more sensitive than the urinary increment method. We conclude that, when taken with food, calcium from the carbonate salt is fully as absorbable as from the citrate, and that the urinary increment method is not sufficiently sensitive to be useful in comparing sources in free-living subjects. Received: 6 April 1998 / Accepted: 6 April 1998     

Absorbability of the calcium in a high-calcium mineral water

The availability of the calcium contained in a high-calcium mineral water (Sangemini), popular in Italy, was compared in 18 healthy women with the availability of milk calcium ingested at the same calcium load, using⁴⁵Ca as the tracer in a randomized cross-over design. At an ingested calcium load of 2.5 mmol, absorption fraction averaged 0.433 for milk and 0.475 for Sangemini water. The mean quotient of the two (Sangemini/milk) was 1.129 (±0.056, SEM,P<0.05). The calcium of Sangemini water is thus highly bioavailable, and at least as bioavailable as milk calcium.     

Sodium and Bone Health: Impact of Moderately High and Low Salt Intakes on Calcium Metabolism in Postmenopausal Women

High salt intake is a well‐recognized risk factor for osteoporosis because it induces calciuria, but the effects of salt on calcium metabolism and the potential impact on bone health in postmenopausal women have not been fully characterized. This study investigated adaptive mechanisms in response to changes in salt and calcium intake in postmenopausal women. Eleven women completed a randomized cross‐over trial consisting of four successive 5‐wk periods of controlled dietary intervention, each separated by a minimum 4‐wk washout. Moderately low and high calcium (518 versus 1284 mg) and salt (3.9 versus 11.2 g) diets, reflecting lower and upper intakes in postmenopausal women consuming a Western‐style diet, were provided. Stable isotope labeling techniques were used to measure calcium absorption and excretion, compartmental modeling was undertaken to estimate bone calcium balance, and biomarkers of bone formation and resorption were measured in blood and urine. Moderately high salt intake (11.2 g/d) elicited a significant increase in urinary calcium excretion (p = 0.0008) and significantly affected bone calcium balance with the high calcium diet (p = 0.024). Efficiency of calcium absorption was higher after a period of moderately low calcium intake (p < 0.05) but was unaffected by salt intake. Salt was responsible for a significant change in bone calcium balance, from positive to negative, when consumed as part of a high calcium diet, but with a low calcium intake, the bone calcium balance was negative on both high and low salt diets.