Radioisotopic studies concerning the efficacy of standard washing procedures for the cleansing of hair before zinc analysis.
(65/94)
Various standard procedures were investigated in relation to the removal of exogenously applied 65Zn from human hair and endogenously incorporated 65Zn from rat hair. Human hair was found to adsorb zinc and a variety of other metal ions from aqueous solutions in a manner which suggested some ion-exchange capacity. Uptake of zinc varied considerably between human hair samples, but in most cases accumulation of zinc occurred rapidly and often resulted in hair zinc levels several-fold higher than found in control samples. Extraction of zinc and other metal ions was greatest after treatment with disodium EDTA and sodium lauryl sulfate than after washing with water or aqueous Triton X-100. However, no procedure effectively removed all exogenous zinc, while all treatments extracted varying proportions of the endogenous zinc component. Because of the inability of standard washing procedures to remove exogenous zinc without reducing endogenous or indicator zinc levels, use of hair zinc analyses to indicate nutritional zinc status are inadvisable if hair zinc contamination is likely to have occurred. (+info)
Bioavailability of zinc to rats from defatted soy flour, acid-precipitated soy concentrate and neutralized soy concentrate as determined by intrinsic and extrinsic labeling techniques.
(66/94)
The bioavailability of 65Zn from intrinsically and extrinsically labeled soy flour, acid-precipitated soy concentrate and neutralized soy concentrate was evaluated in rats. Weanling rats were fed marginally zinc-deficient diets, providing 8 ppm zinc from one of these three soy products, for 7 days. The rats then received a radioactively labeled test meal, identical in composition to the previous diet except that the soy product was either intrinsically or extrinsically labeled with 65Zn. After the test meal the rats were again fed diets the same as those consumed prior to the test meal. Whole-body retention of 65Zn at 24 hours and 12 days as well as 65Zn retained in tibias of rats given meals containing neutralized concentrate-based meals was significantly lower than for rats given meals containing the soy flour or acid-precipitated concentrate. In addition, retention of 65Zn from the extrinsically labeled acid-precipitated concentrate-based meal was significantly higher than from the same product intrinsically labeled. These findings confirm the results of previous feeding studies from which it was suggested that neutralization of soy protein concentrates reduces zinc bioavailability to the rat. In addition, the results are taken to suggest that experimental conditions may influence the validity of the extrinsic labeling technique for zinc. (+info)
The effect of individual components of soy formula and cows' milk formula on zinc bioavailability.
(67/94)
Zinc absorption from human milk, cows' milk formulas, and soy formulas was studied in human adults by a radioisotope technique using 65Zn and whole body counting. Individual dietary components were investigated for effects on zinc absorption. Phytate was found to have a strong inhibitory effect on zinc absorption; addition of phytate to cows' milk formula (yielding a phytate concentration similar to that of soy formula) resulted in a decrease in zinc absorption from 31 to 16% similar to the absorption for soy formula (14%). Carbohydrate source, calcium, and zinc levels of the diet did not affect zinc absorption significantly. Iron supplementation of cows' milk formula decreased zinc absorption from 24 to 18% although this decrease was not found to be significant (p less than 0.1). Absorption of zinc from a whey-adjusted cows' milk formula was higher (31%) than from a nonmodified cows' milk formula (22%). Increasing the zinc supplementation level in cows' milk formula but not in soy formula increased zinc absorption to approximate that from breast milk. It is suggested that reduction of phytate content of soy formula may be a more effective avenue of modification than increased level of zinc supplementation. (+info)
Determination of ultrafiltrable zinc in plasma by flameless atomic absorption spectrophotometry.
(68/94)
Ultrafiltrable zinc can be determined in small volumes of plasma by using Amicon ultrafiltration membrane cones and either flameless atomic absorption spectrophotometry or 65Zn. The ultrafiltration membrane cone is made sufficiently zinc-free by acid washing, followed by rinsing with de-ionized water. Within-run CVs were 12 and 10%, respectively, for the two methods. Matrix effects are compensated for by using standards in solutions with an inorganic matrix that simulates the sample matrix. Results for ultrafiltrable zinc by the two techniques agreed, and agreed with previously published data obtained by different ultrafiltration techniques. The mean (and SD) percentage of plasma zinc that was ultrafiltrable in 12 control subjects was 1.0 (0.5) by AAS and 0.7 (0.3) by 65Zn. (+info)
Effect of dietary zinc sources and pregnancy on zinc utilization in adult women fed controlled diets.
(69/94)
Five nonpregnant and 10 pregnant women participated in 21-day confined metabolic studies. Two diets each providing 16 mg of zinc per day were fed. In one diet 70% of the total zinc was provided by animal products and 30% was contributed by plant sources. In the second diet the proportions were reversed. Apparent absorption of zinc was determined using the balance technique. During the last 15 days of the study, zinc intake was only slightly greater than the amount of zinc excreted in feces. Mean apparent absorption values did not exceed 5% and did not vary due to diet or pregnancy. Zinc bioavailability was also assessed by measuring the apparent absorption of a stable isotope of zinc (70Zn) added to the diet. There was no significant effect of either diet or pregnancy on 70Zn absorption, which averaged about 25%. Serum zinc values were normal throughout the study and did not change significantly as a function of diet. The pregnant women, however, maintained values that were 19-27% lower than those of the nonpregnant women. In summary, the substitution of animal sources of zinc by plant products did not reduce zinc bioavailability or alter zinc utilization. (+info)
A kinetic study of the in vivo incorporation of 65ZN into the rat hippocampus.
(70/94)
Previous autoradiographical studies utilizing 65Zn demonstrated an apparent concentration of 65Zn in the mossy fiber boutons of the hippocampus. To examine the speciation of the 65Zn pool found in this neuronal pathway, we investigated the in vivo incorporation of systemic 65Zn into rat hippocampus compared with other brain regions. We were especially interested in kinetically assessing the zinc associated with three previously identified cytosolic zinc-binding species found in the hippocampus. The hypothesis that two of these cytosolic zinc-binding species, a metallothionein-like protein and a putative zinc-glutathione complex, may be responsible for the sequestration of zinc in the hippocampus was tested. It was confirmed that the t 1/2 of hippocampal zinc is longer than other brain regions that were studied. Furthermore, we observed that 65Zn is incorporated into three cytosolic zinc-binding species in the hippocampus as resolved using Ultrogel AcA 34 gel permeation chromatography. One of these species, the putative zinc-glutathione complex, accumulates zinc more slowly than the other species. The data suggest that the putative zinc-glutathione complex may represent an important 65Zn pool in the hippocampus. This finding is in accordance with out hypothesis that a zinc-binding species, specifically, the putative zinc-glutathione complex, may be responsible for the sequestration of zinc in the hippocampal mossy boutons. (+info)
Zinc absorption and its relationship to intestinal metallothionein.
(71/94)
This study examined the relationship between zinc absorption and metallothionein. Mice injected intraperitoneally with ZnCl2 (2 mmoles) were found within 18 hours to have increased levels of intestinal metallothionein but an apparent decrease in 65Zn absorption. Induction of metallothionein with lower levels of ZnCl2 (0.2 or 0.5 mumoles) resulted in an apparent increase in 65Zn absorption. Isotope dilution experiments showed that intraperitoneal injections of 2 mumoles of ZnCl2 had resulted in a 500-fold dilution of the available 65Zn pool. Mild stress of the animals was shown to increase both 65Zn absorption and intestinal metallothionein. Actinomycin D administered 4 hours prior to ZnCl2 or stress, prevented the induction of metallothionein and obliterated the increase in 65Zn absorption. These results indicate that zinc absorption is directly proportional to intestinal metallothionein levels and imply a significant role for metallothionein in zinc absorption. (+info)
Comparative measurement of zinc absorption in rats with stable isotope 70Zn and radioisotope 65Zn.
(72/94)
The use of stable isotopes in a study on zinc bioavailability was evaluated in rats by comparing the zinc absorption of a stable isotope 70Zn and a radioisotope 65Zn simultaneously. The rats of low zinc status were obtained by feeding 1.2% phytic acid from sodium phytate and 12 ppm zinc from zinc sulfate in a semipurified diet for 14 days. The rats were then randomly assigned into five groups of ten rats. The rats were intubated with a test diet mixture with a phytate:zinc molar ratio of 0, 6.25, 12.5, 25 or 50 along with one microCi of 65Zn and 0.02 mg of 70Zn in 2.5 ml of intubating solution. Four hours after the intubation, rats were allowed to consume the diets having the same phytate:zinc ratio as used for intubation ad libitum. Feces were collected every 24 hours for a total of 168 hours. The 65Zn and 70Zn content of diets and fecal samples were determined and the percent of zinc absorption was calculated. The results of this study indicated that the zinc absorption determined by these two isotopes were highly correlated with a correlation coefficient ratio of 0.914. (+info)