Zinc body content

Absorbed zmc is transported to the liver by the portal circulation where active incorporation into metalloenzymes and plasma proteins such as albumin and a2"macroglobulin occurs. Blood plasma contains less than 1% of the total body content of zinc and lies within a narrow concentration interval 80 to 120pg/dL (12 to 18 imol/L). About 80% of plasma zinc is associated with albumin and most of the rest... 

Total adult body content of zinc is about 2 to 2.5 g and the metal is present in the cells of aU metabolically active tissue and organs. About 55% of the total is found in muscle and approximately 30% in bone. The prostate, semen, and the retina have particularly high local concentrations of zinc. Almost aU zinc in a red cell is in the form of carbonic anhy-drase so that red cell zinc concentration is about 10 times higher than plasma. Hemolysates normally have about 50 fig Zn per g Hb, and total leukocyte zinc is normally about 100 25(J,g/10 cells. 

Various estimates have been made of the whole body content, based initially on direct cadaver analysis and more recently by isotope dilution techniques (Kennedy et al., 1978). Values between 1-2 g for an adult are quoted. Since the greatest amount of zinc is found inside cells, the average tissue concentration is higher than that found in body fluids. Zinc is present in all metabolically active tissue and some results obtained from tissue obtained at autopsy of accident victims, are shown in Table 5. These were obtained using neutron activation analysis (Smith, 1967) and by flame MS (Lyon et al., 1989, Martin et al., 1992). 

The body content in a 70-kg man is about 2.5 g zinc, which is mainly in muscles (60%) and skeleton (30%) [32]. The remaining 10% is distributed in all tissues with highest concentrations in eyes, prostate, and hair. All tissue levels depend on age. 

Let us first consider, as an example, the copper-zinc system of alloys.1 The ordinary yellow brass of commerce is restricted in composition to the first (copper-rich) phase of the system. This phase, which has the face-centered cubic structure characteristic of copper, is followed successively, as the zinc content is increased, by the /3-phase (body-centered cubic),... 

Metallothioneins are a group of small proteins (about 6.5 kDa), found in the cytosol of cells, particularly of liver, kidney, and intestine. They have a high content of cysteine and can bind copper, zinc, cadmium, and mercury. The SH groups of cysteine are involved in binding the metals. Acute intake (eg, by injection) of copper and of certain other metals increases the amount (induction) of these proteins in tissues, as does administration of certain hormones or cytokines. These proteins may function to store the above metals in a nontoxic form and are involved in their overall metaboHsm in the body. Sequestration of copper also diminishes the amount of this metal available to generate free radicals. 

Whole-body zinc content of terrestrial isopods seems to reflect soil zinc levels and may be a useful indicator of soil contamination (Hopkin et al. 1989). Porcellio scaber, a terrestrial isopod known as a woodlouse, is recommended as a biological indicator of zinc contamination because of the positive correlation between zinc content in soil or leaf litter and woodlouse hepatopancreas. Zinc content in Porcellio, litter, and soil near a zinc smelter, in mg/kg DW, was >1000 in whole isopod, >9000 in hepatopancreas, >10,000 in titter, and >50,000 in soil (Hopkin et al. 1986). 

The 1000 mg/kg supplement had no adverse effects on milk production, feed intake, body weight, general health, or reproduction there was a moderate increase in Zn content of plasma and milk. Cows fed the 2000 mg Zn/kg diet, however, had decreased milk yield and feed intake after several weeks calf weights were lower adverse effects reversed when excess zinc was removed from diet. 

At present, Polish standards only limit zinc content in juices and nectars. The maximum limit for zinc in these products is 5 pg per g (Dz. U., 2003). The Joint FAO/WHO Expert Committee recommends the PTWI should not exceed 7000 pg per g (7 mg per g) of body weight (WHO, 1989). 

Significant differences in zinc content occur in potatoes. The zinc content ranges Ifom 1.8 to 10.2 p,g/g FW (Andre et al., 2007 Randhawa et al, 1984 Rivero et al., 2003). Yellow-fleshed potatoes from different cultivars contain zinc in 0.5-4.6 p,g/g FW (Dugo et al., 2004). Zinc is needed for the body s immune system to properly work and is involved in cell division, cell growth, and wound healing. The US RDA is 15-20 mg. 

Persistent acute body zinc loss has resulted in many symptoms in addition to taste and smell dysfunction if losses continue at significant levels for periods of 14 days or more. These symptoms Include mental confusion, cerebellar dysfunction, including intention tremor and ataxia, an erythrematous, Intracrural rash, buccal epithelial lesions and ulcers, and acute toxic psychosis (,6). The altered mental state of these patients can be related to the rapid depletion of the relatively high zinc content in the limbic system of the brain (16.17), demonstrating that zinc can cross the blood brain barrier bidirectionally, dependent upon the gradient, and that it can be readily mobilized from brain tissue. 

Definitions of Zinc Deficiency. It is clear that zinc deficiency can be defined only with difficulty since the zinc content of a single body fluid or tissue level cannot provide a definitive estimate of body zinc status (If3 ) It is also not possible to rely on the concentration of zinc in several body tissues to estimate body zinc status since differing concentrations in different tissues lead to non-definitive conclusions. 

In a preliminary experiment, weanling male Wistar rats were depleted of zinc by feeding a low zinc basal diet (0.6 yg/g zinc) for two weeks and then repleted by adding 12 yg/g zinc as zinc sulphate. The analysis of the zinc content of the different tissues at weekly intervals for four weeks revealed that the body weight and the total femur zinc were the parameters of choice because the responses were linear with duration of feeding. Moreover, the relative errors of the slopes of the regression lines were minimal (5). The results of this experiment also showed that since depletion did not reduce the variability in these parameters, it was not essential for the assay. 

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