Phosphorus metabolism

Based on limited epidemiologic evidence, fluoride supplements, with or without calcium, estrogen and vitamin D, are used by clinicians for the treatment of osteoporosis. However, knowledge of the effects of fluoride on calcium and phosphorus metabolism in normal animals is limited although Spencer et al. (32) reported that ingestion of fluoride by three osteoporotic men did not affect calcium absorption but caused a decrease in urinary excretion. Moreover, there is a need to determine the long-term effects of fluoride treatment on bone strength and on soft tissues ( ). 

McElroy,W.D. Glass, B., Eds.(1951) Phosphorus Metabolism. Johns Hopkins Press, Baltimore. 

Sutherland, E.W. (1952). The effects of epinephrine and the hyperglycemic factor on liver and muscle metabolism in vitro. In Phosphorus Metabolism. (McElroy, W.D. Glass, B., Eds.), Vol. 2, pp. 577-593. The Johns Hopkins Press, Baltimore. 

The parathyroid hormone content of blood has not been studied sufficiently to yield any data with regard to variation. The functioning of the glands is so closely related to other factors which regulate calcium and phosphorus metabolism that it is impossible to assign differences in these areas to variation in parathyroid function. The variation of the calcium (and phosphorus) in the blood has been noted (p. 55), and this variation, of course, may be due in a substantial degree to differences in parathyroid functioning. 

Inorganic pyrophosphatase [EC 3.6.1.1] plays a central role in phosphorus metabolism by catalyzing the hydrolysis of the phosphoanhydride bond of inorganic pyrophosphate (or, diphosphate PPi). This cleavage reaction acts in conjunction with pyrophosphate-forming ligases to provide an additional thermodynamic impetus for certain biosynthetic reactions. For example ... 

Calcium and phosphorus metabolism Calcium and phosphorus metabolism is influenced by estrogens use caution in patients with metabolic bone diseases associated with hypercalcemia or in renal insufficiency. 

Vitamin D3 is transported to liver where it undergoes a hydroxylation at C-25 into 1a,25-dihydroxyvitamin D3 (calcitriol) (Fig. 64). In the kidney, it undergoes further hydroxylations at different sites, depending on the serum Ca + concentration. The most biologically active metabolite of vitamin D3 is calcitriol, which plays important roles in the regulation of calcium and phosphorus metabolism. It is used for treating bone diseases, but is also involved in the cell proliferation and the inducement of cell differentiation [151]. 

Elsair, J., R. Merad, R. Denine, M. Reggabi, B. Alamir, S. Benah, M. Azzouz, and K. Khelfat. 1980b. Boron as a preventive antidote in acute and subacute fluoride intoxication in rabbits its action on fluoride and calcium-phosphorus metabolism. Fluoride 13 129-138. 

Irving, J. T. Calcium and Phosphorus Metabolism. New York Academic Press 1973... 

Calcium and phosphorus metabolism in relation to lactose tolerance. Lancet 1, 1027-1029. 

Spencer, H., Kramer, L., Norris, C. and Osis, D. 1982B. Effect of small doses of aluminum-containing antacids on calcium and phosphorus metabolism. Am. J. Clin. Nutr. 36, 32-40. 

Vitamin D3 is a precursor of the hormone 1,25-dihy-droxyvitamin D3. Vitamin D3 is essential for normal calcium and phosphorus metabolism. It is formed from 7-dehydrocholesterol by ultraviolet photolysis in the skin. Insufficient exposure to sunlight and absence of vitamin D3 in the diet leads to rickets, a condition characterized by weak, malformed bones. Vitamin D3 is inactive, but it is converted into an active compound by two hydroxylation reactions that occur in different organs. The first hydroxylation occurs in the liver, which produces 25-hydroxyvita-min D3, abbreviated 25(OH)D3 the second hydroxylation occurs in the kidney and gives rise to the active product 1,25-dihydroxy vitamin D3 24,25 (OH)2D3 (fig. 24.13). The hydroxylation at position 1 that occurs in the kidney is stimulated by parathyroid hormone (PTH), which is secreted from the parathyroid gland in response to low circulating levels of calcium. In the presence of adequate calcium, 25(OH)D3 is converted into an inactive metabolite, 24,25 (OH)2D3. The active derivative of vitamin D3 is considered a hormone because it is transported from the kidneys to target cells, where it binds to nuclear receptors that are analogous to those of typical steroid hormones. l,25(OH)2D3 stimulates calcium transport by intestinal cells and increases calcium uptake by osteoblasts (precursors of bone cells). 

Mukai T. [Antagonism between parathyroid hormone and glucocorticoids in calcium and phosphorus metabolism. ]Nippon Naibunpi Gakkai Zasshi 1965 41(8) 950-9. 

Morozova, A.L. (1973). The carbohydrate-phosphorus metabolism in muscles of fish of different ecology (In Russian). Proceedings of All-Union Hydrobiological Society 18,128-136. 

Trusevich, V.V. (1978). Phosphorus metabolism of fish during swimming (In Russian). In Elements of Physiology and Biochemistry in Total and Active Metabolism of Fish (G.E. Shulman, ed.), pp. 145-167. Naukova Dumka, Kiev. 

Ondreicka R, Ginter E, Kortus J. 1966. Chronic toxicity of aluminum in rats and mice and its effects on phosphorus metabolism. Br J Ind Med 23 305-312. 

No studies were located regarding metabolism in humans or animals after inhalation, dermal, or other routes of exposure to white phosphorus smoke or smoke condensates. White phosphorus smoke and condensates of the smoke probably contain some residual unburnt white phosphorus (see Chapter 3 for composition information). For further discussion of white phosphorus metabolism, see Sections 2.3.3.1, 2.3.3.2, and 2.3.3.3 below. 

No studies were located that specifically address white phosphorus metabolism in humans or animals after inhalation exposure. However, since orthophosphate is a stable end-product of the inorganic oxidation and hydrolysis of white phosphorus, it is appropriate to examine data on serum phosphate levels in humans and animals (these data are discussed further in Section 2.2). 

No studies on body burden reduction methods were located. The state of definitive knowledge of white phosphorus metabolism is too limited to permit extensive speculation on methods for reducing body burden. However, it is possible that increasing selective excretion of phosphate may increase the rate of inorganic conversion of white phosphorus to phosphate (this conversion is described in detail in Section 2.3). Since phosphate is a naturally occurring component of the blood s buffering system, this would effectively deactivate the phosphorus. No methods for selectively increasing phosphate excretion were located. 

Forfar et al. (F7) have studied phosphorus metabolism in 2 active cases of idiopathic hypercalcemia. The average retention of phosphorus on a mean intake of 0.9 g/day was 43 % (0.39 g). Morgan et al. (M3) have reported retentions of 46 % and 37 % in two infants, the actual daily retentions being 0.30 g and 0.18 g, respectively. 

PolyP metabolism in E. coli is interesting first of all due to the very intensive investigations of its phosphorus metabolism both in the biochemical and genetic aspects. 

Figure 8.4 Effects of addition of P to a previously starved culture on the activity of phosphorus-metabolizing enzymes in E. coli (1) alkaline phosphatase (2) exopolyphosphatase (3) tripolyphosphatase (4) 1,3-DPGA-polyphosphate phosphotransferase (5) polyphosphate kinase (all in an P -free medium) (l -5 ) with the addition of P . The time of P addition is shown by the arrows (Nesmeyanova et al., 1974a).

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