Calcium metabolism studies

Thermal ionization mass spectrometry has been used extensively in the geological nuclear and analytical sciences for stable isotope measurements A new technique resonance ionization mass spectrometry offers a comprehensive approach to sensitive and selective elemental and isotopic analysis Recent developments in thermal and resonance ionization mass spectrometry are reviewed) and specific applications of the technology to zinc and calcium metabolism studies and to trace element analysis of foodstuffs are summarized ... 

One of the triumphs of the science of nutrition is the careful investigation that linked childhood rickets with vitamin D deficiency. This work, which led to methods for treating the disease, is too familiar to need repetition. A direct consequence of these efforts was the elucidation of the pivotal role played by vitamin D in calcium metabolism, as well as the structural studies that revealed that this compound (102) is in fact a steroid derivative. The past... 

A number of dietary and nondietary variables have been proposed as risk factors for osteoporosis. Among dietary factors, the relation between caffeine intake and bone health has been studied extensively. Although proof that caffeine adversely affects calcium metabolism and is detrimen-... 

Osis et d. 38) have determined calcium and magnesium in urine, diet, and stool for metabolic studies, and Dennler and Drepper39) have determined calcium and magnesium in the sera of sheep and calves. 

F3. Fink, S., and Laszlo, D., A metabolic study following oral calcium 45 administration in a patient with non-tropical sprue. Gastroenterology 32, 689-703... 

Isotope Methods. The isotopes of calcium have relatively short half-lives and are readily counted using liquid scintillation or gamma counters as appropriate to the nuclide. Calcium isotopes may be quantitated in the excreta, blood, tissues or in the whole body. This has made them useful for many nutritional metabolic studies. However, because of safety concerns, radioactive isotopes are cumbersome to work with and many researchers are unwilling to administer them to human beings. This has limited the use of isotopes to those studies in which alternate methods are not available or are imprecise. Methodologies for stable isotopes of calcium, which may be safely used in human being, are becoming available for use in metabolism studies. These will be practical alternatives to radioactive isotopes in the future. 

In attempting to reconcile these findings, it should be pointed out that rats may not be appropriate models for the study of calcium metabolism in humans. Unlike humans, the rat does not undergo epiphyseal plate closure and does not have a significant haversian remodeling sequence (21) Furthermore, rats excrete only l-270 of their calcium intake in their urine whereas humans excrete approximately 20-30% or more. This fact is especially significant, since most of the known effects of phosphates on calcium retention in humans are effected by alterations in urinary calcium. 

We have conducted two human metabolic studies (5,6) to compare the effects of increasing phosphorus intake on calcium utilization in healthy young adults maintained at low (ca. 400 mg/day) and high (ca. 1200 mg/day) levels of calcium intake. Increasing dietary phosphorus, as orthophosphate, caused a slight reduction in fecal calcium and a substantial reduction in urinary calcium losses (Table III). 

Several comprehensive reviews on oxalic acid have been published in which effects on calcium metabolism were discussed (7-11). A review of studies on the effect of oxalic acid on calcium bioavailability in rats and humans is presented in this paper. 

These studies have shown that phosphorus, magnesium and fluoride In the doses used had no effect on the bloavailablllty of calcium, while large doses of zinc given during a low calcium Intake Inhibited the Intestinal absorption of calcium The effect of protein and of certain drugs on calcium metabolism Is also described ... 

The present communication is concerned with calcium balance studies carried out during the Intake of a variety of dietary factors including minerals and protein as well as drugs. The studies were performed In adult males under strictly controlled conditions in the Metabolic Research Unit. The diet was kept constant throughout the relatively long term studies and complete collections of urine and stool were obtained. The composition of this diet was previously described (5). The diet and the excretions in urine and stool were analyzed for calcium throughout the studies. These data formed the basis of calcium balances which were determined for several weeks. Calcium was analyzed by atomic absorption spectroscopy (6). 

In extensive studies of the effect of fluoride In patients with osteoporosis carried out In this Research Unit, a therapeutic dally dose of 45 mg fluoride per day was used as sodium fluoride. The main effect of fluoride on calcium metabolism was a decrease of the urinary calcium, while the fecal calcium did not change and the calcium balance also remained unchanged. Also, the Intestinal absorption of calcium remained unchanged during the high fluoride Intake (Table I), The decrease In urinary calcium, Induced by sodium fluoride, may be due to decreased bone resorption, a very desirable effect for patients with osteoporosis. 

Zinc, A great deal of Information Is available on the effect of calcium on zinc metabolism, particularly In animals (30,31), but only a few studies have been carried out In man (32,33), On the other hand, to our knowledge, no studies have been reported on the effect of zinc on calcium metabolism In man. In studies carried out In this Research Unit, It has been demonstrated that large amounts of zinc significantly decrease the Intestinal absorption of calcium If the zinc supplements are given during a low calcium Intake (34),... 

Weaver, C. M., and Heaney, R. P. (2006c). Clinical approaches for studying calcium metabolism and its relationship to disease. In "Calcium in Human Health" (A. Bendich, ed.),. 433. Humana Press, Totowa, NJ. 

The mechanisms by which 2-PAM exerts its cardiac effects have been studied in experimental animals. At least three classes of action have been attributed to the effects of altered calcium metabolism on autonomic ganglia. A sympathomimetic action of 2-PAM was postulated to explain the increase in blood pressure and the augmented myocardial contractility by one or more of the following mechanisms 2-PAM may not block the release of the endogenous compounds, but may prevent the uptake of catecholamine 1 it may stimulate the release of norepinephrine it Increases myocardial contractility by directly stimulating beta receptors and it increases blood pressure by directly stimulating alpha receptors. 5... 

Fitzgerald et al,54 studied the monitoring of calcium metabolism in patients in the final stages of renal disease using serum by AMS after isotopic labelling with a 41 Ca radiotracer. The authors hypothesized that bone resorption can be studied directly by serial measurements of the 41Ca/Ca,otal ratio in serum after in vivo labelling of the calcium pool with 41 Ca.54... 

There is some evidence, mostly from animal studies, to suggest that high dietary levels of phosphorus, especially if dietary levels of calcium are low, may adversely affect bone mass and calcium metabolism (Greger and Krystofiak 1982). However, in humans there is little direct evidence to indicate that large variations in dietary phosphorus or in the Ca P ratio have any significant influence on calcium utilization or balance (Heaney et al. 1982). Some preliminary findings, however, suggest that the form of phosphorus may influence calcium absorption (Zemel et al. 1982). Hexametaphosphate, as compared with orthophos-... 

Glucocorticoids can even cause osteoporosis when they are used for long-term replacement therapy in the Addison s disease, as has been shown by a study of 91 patients who had taken glucocorticoids for a mean of 10.6 years, in whom bone mineral density was reduced by 32% compared with age-matched controls (SEDA-19, 377 198). However, these results contrasted with the results of a Spanish study in patients with Addison s disease, in which no direct relation was found between replacement therapy and either bone density or biochemical markers of bone turnover of calcium metabolism (alkaline phosphatase, osteocalcin, procollagen I type, parathormone, and 1,25-dihydroxycolecalciferol) (SEDA-19, 377 199). 

Bogoyavlenskaya, N.P. (1959). Study of calcium metabolism aimed to apply Ca45 as a tracer for fish (In Russian). Rybnoye Khozyaistvo 1959,1-55. 

Spencer, H., Vankinscott, V., Lewin, I., and Lasslo, D., Removal of calcium in man by ethylene diamine tetra-acetic acid Metabolic study. /. Clin. Invest. 31, 1023-1027 (1952). 

Physiologically important calcium flow rates can be determined using calcium isotopic tracers without resorting to classical metabolic balance methodology Calcium stable isotopic tracers are sufficiently benign to permit their use in studies of calcium metabolism in children The measurement techniques and clinical protocol for our studies of skeletal development in children are described ... 

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