Zinc excretion

Crustaceans can accumulate zinc from both water and food (USEPA 1987). In uncontaminated waters, the diet is probably the major source of zinc. Absorption from the stomach is efficient and occurs, in part, via the hepatopancreas. When a large pulse of zinc reaches the blood from the stomach, some is excreted, but much is resorbed and stored in the hepatopancreas in a relatively nonlabile form. Ultimately, stored zinc is also excreted, although removal via the gut is unimportant (Bryan et al. 1986). Zinc absorption occurs initially at the gill surface, followed by transport on a saturable carrier in the cell wall, and is most efficient at low dissolved ambient zinc concentrations. Urinary excretion is an important body removal pathway, especially at high dissolved ambient concentrations when it can account for 70 to 80% of total zinc excretion (Bryan et al. 1986). 

No accumulations in 100 mg/kg group zinc excretion rate about twice that of controls. No deaths in 2000 mg/kg group, but growth rate was decreased, anemia evident, tissue copper and iron decreased, and tissue zinc increased (Stahl etal. 1989b). 

Kelsay and co-workers (27,28) observed no effects on iron balance of including 24g/day of NDF from fruits and vegetables however, negative zinc and copper balances were observed. In a second study (29), lower zinc, but not copper, balances were observed at intakes of 25g NDF/day lower intakes (10, 18g NDF) had no effect. In these studies, the effects of oxalates (from spinach) may have affected mineral balances. In a third study, a combination of consuming spinach every other day plus a daily fiber intake of 26g NDF resulted in increased fecal zinc excretion and negative balances (22) ... 

Foster PM, Thomas LV, Cook MW, et al. 1980. Study of the testicular effects and changes in zinc excretion produced by some n-alkyl phthalates in the rat. Toxicol Appl Pharmacol 54 392-398. 

When van Rij and co-workers (3) infused patients with various amino acid preparations, they found urinary zinc excretion to be higher with a sugar-containing preparation than when they used the same preparation without sugar. A unique zinc-binding substance was present in the sugar-containing solution and in the urine of patients infused with it. 

A partial explanation for the effects of alcohol on zinc status may reside in the observations that 1) alcohol increases zinc excretion (21), and 2) the increased zinc excretion precipitates a crisis resulting in a conditioned deficiency in the esophagus and greater susceptibility to carcinogenesis. 

Table VI. Fecal Zinc Excretion (yg/day) in Zinc Deficient Ethanol (ZDE) Fed Animals and Their Corresponding Pair-Fed Zinc...

Urinary excretion of zinc decreased In three out of four subjects as a result of zinc restriction. In one case (Patient 4) there was no decrease In urinary zinc excretion. This was due to the diuretic therapy (hydrochlorothiazide) that he received for mild hypertension during the study. 

Measurement of fecal zinc does not yield the value 0, but rather the total zinc excreted (of dietary and endogenous origin). Thus, determination of total zinc in the diet and the fecal pool will not provide an estimate of the absorption of zinc. However, if the isotopic makeup of the dietary zinc is suitably altered, via administration of a labeled diet, then isotopic analysis of the diet and of the corresponding fecal pool will satisfy the requirements of the above definition. For the simplest case where the natural isotopic composition of a single component of the diet has been altered (single-labeling) an estimate of the fractional absorption (F] ) of the mineral from the labeled diet component, can be made from two simultaneous equations, as follows (See Table I for definitions) ... 

Laboratory tests used to define these syndromes also may be confusing or inadequate (1-4). Urinary zinc excretion may be lower than normal, at normal levels, or elevated, as much as 3-10... 

Increased urinary zinc excretion has been observed from the first day of this syndrome with as much as 1% of the total body... 

Increased urinary zinc excretion coupled with decreased serum zinc concentration and the observed symptoms follow acute zinc depletion with enough consistency that it is relatively simple for an alert physician to establish the diagnosis. However, it is this awareness and the protean nature of the symptoms which complicate its diagnosis. Indeed, the full-blown clinical picture... 

Mean urinary zinc excretion of omnivore and vegetarian subjects were not significantly different from one another nor did the addition of ascorbic acid supplements seem to have a pronounced effect (Table IV). Fecal zinc losses were significantly hlger for the omnivore subjects than for the vegetarian... 

Figure 1. Zinc excretion as percentage of intake, study I (19).

TABLE II. RATIO OF ZINC EXCRETED BY RATS ON SOY PROTEIN DIET VS CASEIN PROTEIN DIET FOLLOWING INTRAPERITONEAL INJECTION... 

In the present study the effect of calcium and phosphorus on zinc metabolism was investigated In adult men by determining metabolic balances of zinc during different intakes of calcium and phosphorus. Three Intake levels of calcium, ranging from 200 to 2000 mg/day, and two Intake levels of phosphorus (800 and 2000 mg/day) were used during a constant dietary zinc Intake of 14.5 mg/day. Increasing the calcium Intake from 200 to 2000 mg and Increasing the phosphorus Intake from 800 to 2000 mg/day had no effect on urinary or fecal zinc excretion nor on zinc retention. absorption studies confirmed... 

Table II shows data of the effect of a high phosphorus Intake on the zinc balance. The phosphorus supplements were given to three patients during different calcium Intakes, namely, during a low calcium Intake of 200 mg per day and during higher calcium Intakes of 800 mg and 2000 mg calcium per day. The phosphorus Intake of the subjects studied was approximately 900 mg per day In the control study and was 2000 mg per day during the high phosphorus Intake. In the control study, during a low calcium Intake and a normal phosphorus Intake of 900 mg per day and a dietary zinc Intake of 17 mg per day, the urinary zinc excretion was relatively high, 1.6 mg/day, the fecal zinc excretion was In the expected range and the zinc balance was positive,...

Studies of the effect of both calcium and phosphorus on the zinc balance which have been carried out In this Research Unit (19. 20) have shown that the zinc balance varies during a normal dietary calcium and phosphorus Intake and ranges from slightly negative to positive values and that the net or apparent absorption of zinc, calculated from zinc balance data, remained unchanged during the addition of the amounts of calcium or phosphorus used In these studies. The zinc balances In the present study have to be considered as maximal balances as the loss of zinc In sweat has not been considered as part of the excretory losses. It has been estimated that the loss of zinc In sweat Is quantitatively as great as the urinary zinc excretion (21). 

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