Plasma zinc

Chool, M. K., Todd, J. K., and Boyd, N. D. "Effect of Carbon Cup Aging on Plasma Zinc Determination by Flameless Atomic Absorption Spectrometry". Clin. Chem. (1975), 21, 632-634. 

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). 

Domestic sheep (Ovis aries) fed a low-zinc diet (2.2 mg Zn/kg DW diet) for 50 days, when compared to those fed a zinc-adequate diet (33 mg Zn/kg DW diet), excreted less zinc (<4 mg daily vs. 23 to 25), consumed less food (409 g daily vs. 898), and had lower plasma zinc concentrations (0.18 mg/L vs. 0.53 to 0.58) a reduction in plasma alkaline phosphatase activity and an increase in plasma zinc binding capacity were also noted (Khandaker and Telfer 1990). Sensitive indicators of zinc deficiency in lambs include significant reductions in plasma alkaline phosphatase activity and plasma zinc concentrations signs were clearly evident in lambs fed 10.8 mg Zn/kg DW diet for 50 to 180 days (Vergnes et al. 1990). A normal diet for lambs contains 124 to 130 mg Zn/kg DW ration vs. 33 for adults (Vergnes et al. 1990). One recommended treatment for zinc-deficient sheep is ruminal insertion of zinc-containing boluses every 40 days bolus zinc release is about 107 mg daily (Khandaker and Telfer 1990). 

Frezza, E.E., Gerunda, G.E., Farinati, F., DeMaria, N., Galligioni, A., Plebani, F., Giacomin, A Van Thiel, D.H. (1994) CCl4-induced liver cirrhosis and hepatocellular carcinoma in rats relation to plasma zinc, copper and estradiol levels. Hepato-Gastroenterology, 41, 367-369... 

Sex hormones can cause changes in metal metabolism, including both increased and reduced plasma zinc concentrations and raised serum copper however, serum magnesium is not affected (191). The clinical importance of these effects is not known. 

Plasma zinc levels are commonly decreased in the elderly (Gil). These authors reported mean ( SD) plasma levels in normal young adults at 12.7 ( 1.4) mmol/liter versus 10.5 ( 4.7) mmol/liter in the elderly intracellular levels (neutrophils) were 1.26 ( 0.28) and 0.95 ( 0.26) nmol/mg protein, respectively. This deficiency is most often due to lack of dietary lean meat, poultry, and fish. As a result, zinc intake is frequently less than the minimum recommended intake of 15 mg/day. Moreover, Zn deficiency is particularly common in individuals with diabetes mellitus, liver and renal diseases, malabsorption, alcohol abuse, and those taking diuretic medications (K13). Interestingly, many of the signs and symptoms of Zn deficiency are the same as those often attributed to the aging process (Table 3). 

Table II. Comparison of Plasma Zinc and Plasma Copper Concentrations Between Epileptics and Age, Sex, Race and Height/Weight Ratio Matched Controls...

Care should be taken in automatically attributing low plasma-zinc values to zinc deficiency. As with calcium a major proportion of plasma zinc is attached to albumin and a reduction in plasma albumin will cause a reduction in total zinc values. In chronic diseases total zinc and albumin show a close relationship [44] and it is perhaps for these reasons that so many diseases are found to be associated with a reduced total plasma zinc. At present it is not clear which is the most important fraction of plasma zinc and consequently it is not justifiable to make any correction for protein alteration as has been suggested for calcium. 

Zinc concentrations in the erythrocyte and plasma decreased significantly (p < 0.01) during zinc restriction in comparison to the stabilization levels. During the early phase of zinc repletion a slight increase in erythrocyte and plasma zinc levels was noted, but these values were not statistically significant in comparison to the zinc-restriction levels. A marked increase in erythrocyte and plasma zinc concentration was observed during the... 

Changes in the plasma zinc concentration were observed within 4 to 6 weeks and correlated with the severity of dietary zinc restriction. Thus, plasma zinc may be very useful in assessment of zinc status in humans provided infections, myocardial infarction, intravascular hemolysis, and acute stress are ruled out ( ). As a result of infections, myocardial Infarction, and acute stress, zinc from the plasma compartment may... 

Our data also indicate that during the zinc-deficient state the subjects were in a more positive balance for zinc. This would suggest that perhaps a test based on oral challenge of zinc and subsequent plasma zinc measurement may be able to distinguish between the zinc-sufficient and the zinc-deficient state in human subjects. A study to test this possibility is currently underway in our laboratory. 

The chemical balance technique is inadequate for the accurate assessment of dietary zinc availability and it does not permit, in any case, an evaluation of zinc availability from the separate components of a composite meal. Furthermore, although measurement of changes in the concentration of plasma zinc (3) following ingestion of pharmacological doses of the metal, has been used in studies of dietary zinc availability, this approach has not been validated with regard to its reliability and it cannot provide absolute data on the absorption of zinc. Indeed the only viable approach that can be followed is one Involving use of a suitable isotopic zinc tracer. 

Factors other than food can also affect zinc absorption and plasma zinc levels. We have recently shown that zinc absorption inpatients with defects of taste and smell taking 110 mg/day of " (100 mg/day as ZnSO)(given daily as four 25 mg doses, the... 

A number of important and, as yet, unexplained discrepancies are apparent in tissue zinc concentrations in this syndrome. Patients with chronic renal disease, with clinical signs and symptoms of zinc deficiency show consistently elevated red blood cell zinc levels (40-42) whereas plasma zinc concentrations have been reported as either low, normal or elevated (40-44). Patients with Kwashiorkor and symptoms of zinc deficiency have... 

Besides the effect of dietary calcium level, the amount of iron, and perhaps the level of other metals, may affect zinc bioavailability. Solomons and Jacob (13) have shown in human subjects that increasing the iron/zinc ratio from 0 1 to 3 1 in solutions containing 25 mg of zinc and corresponding amounts of iron as ferrous sulfate produced a progressive decrease in the plasma zinc response. They further reported that the chemical form of iron was an important determinant of the interaction. Solomons (14) extensively reviewed both inhibitory factors and enhancers of zinc bioavailability found in foods. 

The second step in zinc absorption involves the intracellular interaction of zinc with various compounds which may enhance or impede absorptive processes. In 1969, Starcher noted that radioactive copper, given orally, associated with a low molecular weight protein (25). Subsequently, this mucosal protein was isolated and characterized by Richards and Cousins, who classified it as a metallothionein (26), and who further showed that it was induced in response to zinc administration (5). The appearance of this metallothionein, with properties similar to those described for both rat (27) and human (28) liver metallothionein, appears to be related to changes in both dietary zinc status and plasma zinc levels (5). The synthesis of mucosal metallothionein has been shown to be under transcriptional control (29,30). Menard al. reported that dietary zinc administration resulted in enhancement of metallothionein mRNA transcription and its subsequent translation, to yield nascent metallothionein polypeptides(31). The intestinal metallothionein appearance was correlated to both an increase in mucosal zinc content primarily associated with the protein and with a decrease in serum zinc levels. In addition. Smith e al., using the isolated, vascularly perfused intestinal system, reported an inverse relationship between the synthesis of metallothionein and zinc transfer to the portal system, confirming earlier studies (32). 

Figure 4. The mean increment in plasma zinc concentration ( SEM) at hourly intervals after 7-8 subjects per group received zinc sulfate alone or with ferrous sulfate in an aqueous solution of CocaCola with the amounts of minerals shown. The distinct treatments constituted Fe/Zn ratios of 0, 1 1, 2 1, and 3 1. (Reproduced with permission from Ref. 50. Copyright 1981, American Society for...

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