Calcium absorption complexes

In patients on EDTA therapy, calcium cannot be determined by the Indirect colorimetric or fluorometrlc methods based on the chelation of a calcium - EDTA complex. However, In calcium determinations by atomic-absorption spectroscopy, the complexlng agent Is destroyed In the flame and the direct concentration of calcium can be determined. 

Condensed (poly) phosphates may exert different effects on calcium utilization than the aforementioned effects of simple (ortho-) phosphates. Polyphosphates have a much greater affinity for calcium than do orthophosphates, and soluble calcium-polyphosphate complexes are readily formed in the gastric and intestinal environments. In addition, polyphosphates must be hydrolyzed by an intestinal alkaline phosphatase (27) prior to absorption. We have found polyphosphates to be incompletely (80.5%) hydrolyzed to orthophosphate during the digestive process in young adult males when calcium intake was low only 56% of a 1 g phosphorus supplement was absorbed from a polyphosphate sources as compared to 71% from an orthophosphate source (5). 

Not all calcium present in the diet is absorbed by the small intestine and mechanisms are present to ensure only amounts appropriate to body needs are absorbed. These processes are complex and involve the interaction of special transport protein, vitamin D and parathormone. Thus, abnormalities of calcium metabolism may result from many different disease processes. Diseases affecting the bowel may prevent normal absorption, diseases of the parathyroid gland may result in inappropriate levels of parathormone for calcium requirement and a nutritionally inadequate diet may cause vitamin D deficiency with consequent disordered calcium absorption. 

ESTRAMUSTINE CALCIUM AND DAIRY PRODUCTS i plasma concentrations of estramustine and risk of poor therapeutic response Due to l absorption of estramustine owing to the formation of a calcium-phosphate complex Administer estramustine 1 hour before or 2 hours after dairy products or calcium supplements... 

Cholestasis-linked osteopathy (M. Loeper et al., 1939), which occurs much more frequently in the form of osteoporosis than osteomalacia, can be expected in up to 50% of cases. The pathogenesis is complex. Vitamin D status can be examined by determining 25-OH-cholecal-ciferol in the serum. Intestinal calcium loss and reduced calcium absorption due to vitamin D deficiency are key pathogenetic factors. It is still a matter of debate whether vitamin K deficiency (which can lead to reduced osteocalcin synthesis) and deficiencies in IGF I and II (which can cause dysfunction of the osteoblasts) are possible causes of this condition. Muscle and bone pain are frequent clinical symptoms, occurring mainly in the wrists and ankles. 

With calcium stone disease, magnesium is an inhibitor of stone growth. Magnesium forms complexes with oxalate that are more soluble than calcium oxalate. Increased urinary magnesium therefore inhibits stone formation. Administration of magnesium has been shown to reduce enteral calcium absorption and has been proposed as a treatment for idiopathic hypercalciuric stone formers. However, oral magnesium supplementation may have unpleasant side effects and a positive benefit in terms of reducing stone recurrence has not been demonstrated. ... 

Calcium absorption is reduced by high pH complex-ing agents such as oxalate, phytate, free fatty acids, and phosphate and shortened transit times. These factors are probably of clinical importance only when associated with vitamin D deficiency, marginal calcium intake, or malabsorption disorders. Absorption is also reduced by increased intake of protein, fat, and plant fiber increasing age stress chronic alcoholism immobilization (e.g., prolonged hospitalization) and drugs such as tetracycline, thyroid extract, diuretics, and aluminum-containing antacids. 

Thus, a complex relationship exists among serum Ca + and phosphate, PTH, and vitamin D and its metabolites. Release of PTH in response to low serum Ca + directly mobilizes calcium from bone and increases synthesis of 1, 25-(0H)2D, which in turn mobilizes skeletal Ca + and causes increased intestinal calcium absorption. These effects raise the serum Ca level sufficiently to reduce PTH secretion. The effect of PTH on the kidneys occurs within minutes, whereas the effects of PTH on bone and (indirectly) on intestine take hours and days, respectively. An increase in serum phosphate acts in a way qualitatively similar to that of hypocalcemia to release PTH, increase excretion of phosphate in the proximal tubules, and decrease intestinal phosphate absorption. These events are mediated predominantly by the decrease in serum calcium that accompanies a rise in phosphate concentration. In addition, phosphate may inhibit 25-(OH)D-la-hydroxylase. 

Calcium carbonate is the salt of choice because it contains the highest amount of elemental calcium and is the least expensive (see Table 88-5). The fraction of calcium absorbed is dose-limited, so maximum single doses of 600 mg or less of elemental calcium are recommended. Calcium carbonate tablets should be taken with meals to enhance absorption. Calcium citrate absorption is acid-independent and need not be administered with meals. Although tricalcium phosphate contains 39% calcium, nonabsorbable calcium-phosphorus complexes may limit overall calcium absorption compared to other products. This product may be required for up to 10% of seniors with hypophosphatemia that cannot be resolved with increased dietary intake. Disintegration and dissolution rates vary significantly between products and lots. Products with good disintegration and dissolution rates and lead contents of less than 1 mcg/day should be recommended. 

Bone Toxicity. In addition to its effect on calcium absorption, excess absorbed strontium adversely affects bone development in several ways, leading to the development of rickets in children and young animals. Strontium binds directly to hydroxyapatite crystals, which may interfere with the normal crystalline structure of bone (Storey 1961). In addition, excess strontium may prevent the normal maturation of chondrocytes in the epiphyseal plates of long bones (Matsumoto 1976). Excess strontium apparently interferes with the mineralization of complexed acidic phospholipids that is thought to help initiate the formation of hydroxyapatite crystals in developing bone (Neufeld and Boskey 1994). As a result, affected bone contains an excess of complexed acidic phospholipid and a significantly lower ash weight. 

The manufacturers note that food, milk, dairy products, and calcium supplements reduce the bioavailability of strontium ranelate by about 60 to 70%, when compared with administration 3 hours after a med. This is because divalent cations such as calcium form complexes with strontium ranelate so preventing its absorption. Therefore, strontium ranelate should not be taken within 2 hours of eating, or presumably within 2 hours of any calcium compound. The manufacturer recommends that strontium ranelate should be taken at bedtime, at least 2 hours after eating. ... 

Calcium and magnesium are commonly found in water. Obviously if this assay is to be used with water samples, EDTA must be added. It must be determined using water uncontaminated with organic toxins how much EDTA must be used to compensate for the divalent cations. Often the concentration of divalent cations is determined by atomic absorption spectroscopy. However, these values do not agree with the toxicity relieved by EDTA. Soil samples witii as much as 5 gm calcium (45 mM) per kg soil have been assayed using 2.5 imoles EDTA in each sample (Hillaker, 1996). The calcium is complexed with sulfate and phosphate ions and the calcium is not available to the cell, is not seen by the mechanism that reduces the dye. Levels of soluble calcium and magnesium in water are very low. We have found that 2.5 (imoles of EDTA relieves the inhibition caused by divalent cations in all water and soil samples tested thus far (Botsford, 2000b). 

Until very recently, almost all PVC cables were stabilised with lead salts. These gave good thermal stability and electrical resistance, with low water absorption. When the cable was required to have better flame resistance than inherent in PVC, a small part of the calcium carbonate filler was replaced by antimony trioxide. All such cables perform well and have done for many years. Now, however, the need to focus on ecotoxicity has caused the lead salts to be replaced by a non-heavy metal system, usually a calcium-zinc complex. Likewise, the role of antimony is being questioned and formulators have come up with other solutions. 

The presence of gastric acid promotes the absorption of important nutrients by release of minerals, particularly calcium, from their complexed organic forms. However, low-acid states do not appear to predispose to decreased calcium absorption in humans. In contrast, the absorption of ferric iron is decreased in achlorhydric states and in gastrectomized patients. This deficit is related directly to the low solubility of ferric iron at a pH greater than 5.0. Nevertheless, the absorption of heme iron is not compromised, and no evidence exists for a predisposition to iron-deficiency anemia. In the case of vitamin B12, neither PPIs nor H2 receptor antagonists have been implicated in significant alterations in absorption of this compound. 

Dietary calcium is complexed to food constituents such as proteins, phosphate, and oxalate, from which it needs to be released prior to absorption. The role of gastric acid (or the lack thereof induced by commonly used proton pump inhibiting drugs) in intestinal calcium absorption is not well established, although achlorhydria can impair absorption in the fasted state. 

The kidney is also sensitive to lead exposure, with kidney failure resulting from long-term exposure to toxic levels of lead. Furthermore, toxic levels of lead inhibit other functions of the kidney aside from the primary function of urine production. The nephron of a kidney, which is that portion where blood filtering and urine production takes place, is sensitive to lead. It is well known that the active form of vitamin is produced in the proximal tubules of the nephron. Decreased levels of vitamin D3 in the body results in decreased calcium absorption by the gut, and ultimately affect the strength of bones in a lead-exposed body. Increased levels of lead in blood can lead to protein-lead complexes in the nephron tubules. Gout may be a symptom of such toxicity due to increased reabsorption of uric acid into the bloodstream. Typical measures of renal failure (e.g., blood urea nitrogen, creatine) are elevated as a consequence of lead-induced renal failure. 

Most potentiometric electrodes are selective for only the free, uncomplexed analyte and do not respond to complexed forms of the analyte. Solution conditions, therefore, must be carefully controlled if the purpose of the analysis is to determine the analyte s total concentration. On the other hand, this selectivity provides a significant advantage over other quantitative methods of analysis when it is necessary to determine the concentration of free ions. For example, calcium is present in urine both as free Ca + ions and as protein-bound Ca + ions. If a urine sample is analyzed by atomic absorption spectroscopy, the signal is proportional to the total concentration of Ca +, since both free and bound calcium are atomized. Analysis with a Ca + ISE, however, gives a signal that is a function of only free Ca + ions since the protein-bound ions cannot interact with the electrode s membrane. 

Alkaline-earth metals are often deterruined volumetricaHy by complexometric titration at pH 10, using Eriochrome Black T as indicator. The most suitable complexing titrant for barium ion is a solution of diethylenetriaminepentaacetic acid (DTPA). Other alkaline earths, if present, are simultaneously titrated, and in the favored analytical procedure calcium and strontium are deterruined separately by atomic absorption spectrophotometry, and their values subtracted from the total to obtain the barium value. 

The more highly complexed hydrates of calcium chloride (CaCl2 nH2 O where n > 2) may also exhibit the characteristics of a Class 2 dryiag agent, because the hydrated species can physically absorb additional water to form a saturated solution. The term absorption is used to describe the phenomenon that occurs when a gas or vapor penetrates the soHd stmcture to produce a saturated solution ... 

Fig. 1 Absorption scanning curve of the alizarin complexes of barium (1), strontium (2), calcium (3), magnesium (4) and beryllium cations (5). The amounts appUed were 2 pg in each case.

Acetylcyclohexanone. Method A. Place a mixture of 24-6 g. of cyclohexanone (regenerated from the bisulphite compound) and 61 g. (47 5 ml.) of A.R. acetic anhydride in a 500 ml. three-necked flask, fitted with an efficient sealed stirrer, a gas inlet tube reaching to within 1-2 cm. of the surface of the liquid combined with a thermometer immersed in the liquid (compare Fig. II, 7, 12, 6), and (in the third neck) a gas outlet tube leading to an alkali or water trap (Fig. II, 8, 1). Immerse the flask in a bath of Dry Ice - acetone, stir the mixture vigorously and pass commercial boron trifluoride (via an empty wash bottle and then through 95 per cent, sulphuric acid) as fast as possible (10-20 minutes) until the mixture, kept at 0-10°, is saturated (copious evolution of white fumes when the outlet tube is disconnected from the trap). Replace the Dry Ice-acetone bath by an ice bath and pass the gas in at a slower rate to ensure maximum absorption. Stir for 3 6 hours whilst allowing the ice bath to attain room temperature slowly. Pour the reaction mixture into a solution of 136 g. of hydrated sodium acetate in 250 ml. of water, reflux for 60 minutes (or until the boron fluoride complexes are hydrolysed), cool in ice and extract with three 50 ml. portions of petroleum ether, b.p. 40-60° (1), wash the combined extracts free of acid with sodium bicarbonate solution, dry over anhydrous calcium sulphate, remove the solvent by... 

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