Zinc in plasma

Some of the zinc taken up by the intestinal epithelial cells is rapidly transferred to the portal plasma where it associates with albumin, a2 macroglobulin, and amino acids. About 67% of the zinc in plasma is bound to albumin, and about 3% is stored in liver (Stemlieb 1988). Soluble organozinc complexes are passively absorbed across the plasma membrane of the mucosa of the intestinal villi the soluble, nondiffusable complexes are transported in the intestinal products and excreted in feces (NAS 1979). Zinc loss from urine and sweat is usually small (Casey and Hambidge... 

An endemic zinc deficiency syndrome among young men has been reported from Iran and Egypt, and is characterized by retarded growth, infantile testes, delayed sexual maturation, mental lethargy, anemia, reduced concentration of zinc in plasma and red cells, enlarged liver and spleen, and hyperpigmentation oral supplementation of 30 mg Zn daily had a prompt beneficial effect (Prasad 1979 Elinder 1986). 

Cows and calves fed low-zinc diets of 25 mg Zn/kg ration showed a decrease in plasma zinc from 1.02 mg/L at start to 0.66 mg/L at day 90 cows fed 65 mg Zn/kg diet had a significantly elevated (1.5 mg Zn/L) plasma zinc level and increased blood urea and plasma proteins (Ram-achandra and Prasad 1989). Biomarkers used to identify zinc deficiency in bovines include zinc concentrations in plasma, unsaturated zinc-binding capacity, ratio of copper to zinc in plasma, and zinc concentrations in other blood factors indirect biomarkers include enzyme activities, red cell uptake, and metallothionein content in plasma and liver (Binnerts 1989). 

The determination of zinc in plasma, whole-blood and urine... 

We have previously shown that levels of tracer zinc In plasma, red blood cells, whole blood(21) or urlne(22) are closely correlated with absorption when measured under specific controlled conditions. These conditions Include measurement of subjects fasted overnight and oral administration of carrier free tracer. The relationship between plasma Zn-69m activity and absorption estimated from total body retention of Zn-69m was determined... 

As metabolic balance techniques cannot separate the contribution of malabsorption from that of endogenous loss, collaborators at the Division of Nutrition, University of Sao Paolo Medical School at Rlbeirao Preto, Brazil and I undertook to assess Sn Zn interaction using the change-in-plasma-zinc approach. Healthy volunteers received 12.5 mg of zinc as 55 mg of zinc sulfate in 100 ml of CocaCola either alone (control) or with 25, 50 or 100 mg of tin as stannous chloride to constitute 2 1, 4 1 and 8 1 Sn/Fe ratios. We measured the change in plasma zinc concentration at hourly Intervals over a 4-h period. None of the treatments produced any significant decrement in the uptake of zinc in plasma (61) (Table V). Thus, unlike the dramatic effect of even lesser ratios of Fe/Zn (above), the plasma appearance of zinc was unaffected by soluble, inorganic, divalent tin ions. 

About two-thirds of the zinc in pLasma is loosely bound to albumin. Most of the remaining zinc is tightly bound to other plasma proteins. A small fraction (2-37o) of plasma zinc is weakly bound to amino adds. The amino acids that most avidly bind zinc are histidine and cysteine. Amino add-associated zinc enters the glomerular filtrate and thus is a source of the zinc ions destined for excretion in the urine Most of the filtered zinc is reabsorbed and is prevented from immediate excretion. The zinc in red blood cells is bound to car nic anhydrase. Carbonic anhydrase is present at a level about 0,1% that of hemoglobin in the red blood cell on a poweight basis. The zinc content of mitochondria is about 1 nmol/mg protein (Unk and Jagow, 1995). 

Plasma zinc levels vary with sex, age, time of day, geographic location, and time elapsed since the last meal prior to phlebotomy. The normal range for an adult is probably 70-95 jUg/dL of plasma. Approximately 60% of zinc in plasma is bound to albumin, 30-40% to an 2-macroglobulin of unknown function, and a small amount to transferrin (Chapter 29) and amino acids, particularly cysteine and histidine. Copper does not compete with zinc for binding sites on albumin. Zinc newly absorbed from... 

Kelson JR (1980) Criticism of the proposed selected method of direct measurement of zinc in plasma by atomic absorption spectroscopy. Clin Chem 26 349-350. 

It is important to distinguish between changes in zinc metabolism which occur as a secondary effect of disease, injury, infection and drug therapy and alterations caused by a primary nutritional zinc deficiency. There is confusion in the literature because a number of unrelated causes can temporarily lower the concentration of zinc in plasma, and this is reported uncritically as evidence of nutritional depletion. Since a high proportion of zinc in plasma is albumin bound, any circumstance which lowers plasma albumin wiil also lower plasma zinc. For example, the changes seen in severe liver disease are primarily caused by a failure of hepatic synthesis of plasma proteins such as albumin. This results in problems in the distribution of zinc and eventual tissue depletion. It is questionable whether zinc supplementation of diet is worthwhile without some restoration of hepatocyte function, by effective treatment of the underlying disease (Mills et al., 1983). 

The concentration of zinc in plasma/serum is lower than in the cellular components of blood, and for healthy persons is around 1 mg/L. 

Peaston, R.T. (1973). Determination of copper and zinc in plasma and urine. Medical Laboratory Technology, 30, 249. 

Shaw, J.C.L, Bury, A.J., Barber, A., Mann, L. and Taylor, A. (1982). A micro method for the analysis of zinc in plasma or serum by atomic absorption spectrophotometry using a graphite furnace. Clin. Chim. Acta, 118, 229. 

Smith, J.C., Butrimovitz, G.P. and Purdy, W.C. (1979). Direct measurement of zinc in plasma by atomic absorption spectrophotometiV- Clin. Chem., 25(8). 1487. 

O Dell, B. L. (2000). Role of zinc in plasma membrane function. /. Nutr. 130,1432S-1436S. 

Absorption, Distribution, Metabolism, and Excretion. Absorption of zinc in humans after oral exposure to high levels has been well described (Aamodt et al. 1983 Hunt et al. 1991 Reinhold et al. 1991 Sandstrom and Abrahamson 1989 Sandstrom and Cederblad 1980 Sandstrom and Sandberg 1992 Spencer et al. 1985). However, quantitative evidence of zinc absorption in humans after inhalation or dermal exposure is very limited. It is known that workers exposed to zinc oxide fumes who experience toxic effects have elevated levels of zinc in plasma and urine (Hamdi 1969). 

Araki, S., Aono, H., Fukahori, M., Tabuki, K., 1984. Behavior of lead and zinc in plasma, erythrocytes, and urine and ALAD in erythrocytes following intravenous infusion of CaEDTA in lead workers. Arch. Environ. Health 39, 363—367. 

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