Human calcium metabolism

In addition to the well-known iron effects on peroxidative processes, there are also other mechanisms of iron-initiated free radical damage, one of them, the effect of iron ions on calcium metabolism. It has been shown that an increase in free cytosolic calcium may affect cellular redox balance. Stoyanovsky and Cederbaum [174] showed that in the presence of NADPH or ascorbic acid iron ions induced calcium release from liver microsomes. Calcium release occurred only under aerobic conditions and was inhibited by antioxidants Trolox C, glutathione, and ascorbate. It was suggested that the activation of calcium releasing channels by the redox cycling of iron ions may be an important factor in the stimulation of various hepatic disorders in humans with iron overload. 

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. 

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. 

Effect of Dietary Protein, Calcium, and Phosphorus on Calcium Metabolism in Humans... 

Ginis, I., Zaner, K., Wang, J.-S., Pavlotsky, N., Tauber, A. I. (1992). Comparison of actin changes and calcium metabolism in plastic- and fibronectin-adherent human neutrophils. J. Immunol. 149, 1388-94. 

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. 

A number of observations both in experimental animals and in humans are suggestive of a crucial role for dietary calcium in regulating blood pressure (Villar et al. 1986 Karanja and McCarron 1986 McCarron et al. 1984, 1982 McCarron 1985, 1983, 1982 Belizan et al. 1983A,B). For example, laboratory rats fed insufficient calcium experience a rise in blood pressure. Increasing the calcium intake either decreases blood pressure or reduces the development of high blood pressure in animals predisposed to hypertension (Karanja and McCarron 1986). Furthermore, disturbances in calcium metabolism, including a depression in serum ionized or free calcium, have been reported in spontaneously hypertensive rats, as well as in untreated patients with hypertension. 

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-... 

Although bone is not considered a major calcium sensing organ in humans, the cells of bone tissue control over 99% of the human body s calcium content. The principal calcium sensors that regulate bone calcium uptake and release are in the parathyroid glands. Bone function is also modified by vitamin D and by calcium transport in the kidney and intestine. These indirect mechanisms of controlling bone calcium metabolism are beyond the scope of our considerations here. In spite of processing... 

Aub JC, Evans Rd, Gallagher DM, et al. 1938. Effects of treatment on radium and calcium metabolism in the human body. Ann Intern Med 11 1443-1463. 

Isotope amount needed, calculation, 44 typical uses, 144-54 Acetylacetonate, synthesis, 110-11 Adults, calcium metabolism, 36t,38t Alanine, 159 Amino acid composition human bone collagen, 197t of prehistoric bones, 196 Ammonia, 132... 

For acute exposure, ipecac should be administered and lavage performed. The use of single- or multiple-dose activated charcoal is supported by in vitro binding experiments and some animal data, and charcoal hemoperfusion may be a useful adjunct. Forced potassium diuresis appears to be harmful. Flemodial-ysis is also recommended with potassium administration. Since calcium metabolism is disturbed, supplementary calcium is indicated. The use of traditional metal chelators such as dimercaprol (British antilewisite) and penicillamine is not supported by the available evidence. In fact, the use of penicillamine may lead to redistribution of thallium into the central nervous system. Multiple animal studies have found evidence of enhanced elimination and improved survival with Prussian blue however, despite the fact that many humans have been treated with Prussian blue, the data presented are insufficient to judge its true efficacy. Despite this, one publication notes that... 

Traba M, Navarro A, Marin C, et al. A comparative study of 25-hydroxyvitamin D3 separation in human serum. In Norman AW, Schaefer K, Herrath DV, Grigoleit H-G, eds. Vitamin D, chemical, biochemical and clinical endocrinology of calcium metabolism. New York W de Gryter, 1982 805-7. 

Freeman, S.P.H.T. et al., Human calcium metabolism including bone resorption measured with 41Ca tracer, Nucl. Instrum. Methods Phys. Res. Sect. B, 123, 266, 1997. 

The action of vitamin D in human and animal organisms is primarily related to calcium metabolism and the mineralization of bones and teeth, although the mechanism of these processes has not yet been unequivocally confirmed. The cooperation of vitamins A and K is necessary for the proper functioning of vitamin... 

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