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At least 19 recordsLinked to original sources
PubMed1995

Zinc absorption estimated by fecal monitoring of zinc stable isotopes validated by comparison with whole-body retention of zinc radioisotopes in humans.

Knowledge about zinc availability from human diets is limited due to methodological difficulties. Recently developed stable isotope techniques for estimating dietary zinc absorption were compared with radioisotope techniques in five men and three women. Stable and radioactive zinc isotopes were simultaneously administered. Fecal excretion of the isotopes as well as whole-body retention of the radioactive zinc isotope was monitored. Concentration of stable zinc isotope label in fecal samples was determined by inductively coupled plasma mass spectrometry by fully quantitative measurements and from inductively coupled plasma mass spectrometry isotope ratios combined with analysis of total zinc content using atomic absorption spectrometry. Zinc absorption estimated from whole-body retention was 27 +/- 6% (mean +/- SD), estimated zinc absorption obtained by fecal monitoring of radioisotope was 26 +/- 9%, and the two stable zinc measurements resulted in values of 29 +/- 12 and 33 +/- 12%, respectively. There was no significant difference in zinc absorption estimated from whole-body retention and with the fecal monitoring methods. Recovered stable zinc isotope label was significantly lower than recovered radioisotope. For individual fecal samples, systematic differences of 16% and 12%, respectively (P < 0.05), between the radioisotope recovery and the recovery of stable isotopes with the two methods for measurement was observed. The stable zinc isotope technique for measurement of zinc absorption resulted in mean results similar to those of the radioisotope technique, but with a larger variation in the measurements.

Adult↗
PubMed1997

Compartmental analysis of zinc kinetics in mature male rats.

A compartmental model of zinc kinetics in mature male rats was developed. The model was based on zinc and radioisotopic zinc measured in samples of plasma, skeletal muscle, kidneys, testes, spleen, bone, and intestinal segments collected at various times for up to 4 days after 65Zn was injected intravenously. Zinc intake, excretion of zinc and 65Zn in urine and feces, and the whole body retention of 65Zn were also determined. Other data used to develop the model included published information on zinc concentration and zinc kinetics in tissues that were not sampled. In the model, the intestinal tract was represented by five compartments. Plasma, spleen, kidneys, and testes were each represented by an individual compartment. In contrast, two compartments each were used to represent exchangeable zinc in liver, bone, skeletal muscle, skin, and red blood cells. The present model extends earlier models of zinc kinetics, describes the distribution of zinc in the whole body, and may provide a means to evaluate the influence of either pathophysiological conditions or dietary extremes on the metabolism of zinc.

Animals↗
PubMed1978

Induction by alpha-mercapto-beta-arylacrylic acids of low-molecular-weight zinc-binding protein in rat liver.

Intraperitoneal injections of alpha-mercapto-beta-(2-furyl)acrylic acid (MFA) induced incorporation of zinc into a low-molecular-weight metalloprotein fraction in rat-liver cytosol. Cytosol of control rats contained little or none of this material. alpha-Mercapto-beta-(2-thienyl)acrylic acid induced less incorporation of zinc in this fraction than did MFA. Twenty-two hours after administration of 65ZnSO4 (50 mumol/kg) and MFA (200 mumol/kg), serum concentrations of both total and radioisotopic zinc were markedly elevated, compared to serum concentrations in rats administered only 65ZnSO4. Further, in livers of MFA-treated rats, radioisotopic zinc concentration was significantly greater in all cytosol zinc-containing proteins resolved by gel chromatography, but total zinc was elevated only in the metallothionein fraction and not in proteins of higher molecular weight. This appears to be the first example of induction of a metallothionein-like protein by a procedure not involving food restriction or administration of metal salts.

Acrylates↗
PubMed1979

Zinc absorption in the rat determined by radioisotope dilution.

Zinc absorption in rats was examined by use of an isotope dilution technique. Young rats and mature rats fed varying levels of dietary zinc were injected intramuscularly with 65Zn. Nine days later, a zinc balance study was begun and continued for 5 days. The rats were then decapitated and the intestines and kidneys were removed and analyzed for zinc and 65Zn content. The feces were analyzed for zinc and 65Zn content and the specific activities of the intestines and kidneys were used to compute the contribution of endogenous zinc to total daily zinc excretion and thus calculate the true daily absorption of zinc. The zinc concentration of the intestines and kidneys did not differ significantly among groups but the specific radioactivity in these organs decreased as dietary zinc intake increased. Endogenous zinc excretion was greatest in mature rats and young rats fed the highest level of dietary zinc. Mature rats actually absorbed as much or more zinc than young rats fed the same dietary level of zinc. The results demonstrate that zinc homeostasis in rats is maintained by zinc secretion from the intestine rather than by regulation of zinc absorption.

Aging↗
PubMed1993

Clustering of the acetylcholine receptor by the 43-kD protein: involvement of the zinc finger domain.

A postsynaptic membrane-associated protein of M(r) 43,000 (43-kD protein) is involved in clustering of the nicotinic acetylcholine receptor (AChR) at the neuromuscular junction. Previous studies have shown that recombinant mouse 43-kD protein forms membrane-associated clusters when expressed in Xenopus oocytes. Coexpression with the AChR results in colocalization of the receptor with the 43-kD protein clusters (Froehner, S. C., C. W. Luetje, P. B. Scotland, and J. Patrick, 1990. Neuron. 5:403-410). To understand the mechanism of this clustering, we have studied the role of the carboxy-terminal region of the 43-kD protein. The amino acid sequence of this region predicts two tandem zinc finger structures followed by a serine phosphorylation site. Both Torpedo 43-kD protein and the carboxy-terminal region of the mouse 43-kD protein bind radioisotopic zinc. Mutation of two histidine residues in this predicted domain greatly attenuates zinc binding, lending support to the proposal that this region forms zinc fingers. When expressed in oocytes, the ability of this mutant 43-kD protein to form clusters is greatly reduced. Its ability to interact with AChR, however, is retained. In contrast, a mutation that eliminates the potential serine phosphorylation site has no effect on clustering of the 43-kD protein or on interaction with the AChR. These findings suggest that protein interactions via the zinc finger domain of the 43-kD protein may be important for AChR clustering at the synapse.

Amino Acid Sequence↗
PubMed1984

Comparative pharmacokinetics of [65Zn]zinc sulfate and [65Zn]zinc pantothenate injected intravenously in rabbits.

The pharmacokinetics of zinc sulfate were compared with those of a new zinc salt, pantothenate, in rabbits. Each salt was administered at a dosage of 3.3 microCi of zinc-65/kg of body weight. The measured pharmacokinetics of the two compounds responded to a two-compartment open model. The urinary elimination of the two salts was similar, as was their localization in the skin and fur, but zinc pantothenate was fixed by the liver to a lesser extent than was zinc sulfate.

Animals↗
PubMed2006

An approach based on the SIR measurement model for determining the ionization chamber efficiency curves, and a study of 65Zn and 201Tl photon emission intensities.

The measurement model used to determine ionization chamber efficiency curves accounts from the outset for impurity corrections and beta spectrum shapes. The curves are represented by exponentials of polynomials whose coefficients are adjusted using non-linear least-squares minimization. The curves are validated by comparing with SIR key comparison reference values (KCRVs) and other published curves. The associated covariance matrix is also evaluated. Deviations from model predictions for 65Zn and 201Tl using recommended nuclear data are studied.

Algorithms↗
PubMed2002

Foliar and root uptake of 134Cs, 85Sr and 65Zn in processing tomato plants (Lycopersicon esculentum Mill.).

The results of an experimental study on the behaviour of 134Cs, 85Sr and 65Zn in processing tomato plants grown in peat substrate are presented. Plants were contaminated by wet deposition of 134Cs, 85Sr and 65Zn, either by sprinkling the above ground part at two phenological stages or by administering 134Cs, 85Sr and 65Zn to the soil. The plants contaminated at the second phenological stage intercepted 38.3% less than those contaminated at the first stage, although leaf area increased by more than double. Transfer coefficients from peat soil to ripe fruit for 134Cs are significantly higher than those for 85Sr and 65Zn. Leaf to fruit transfer coefficients for 134Cs are one order of magnitude higher than for 65Zn and two orders higher than for 85Sr. Only when deposition affects fruits, as at the second phenological stage, are transfer coefficients to fruits similar for the three radionuclides.

Absorption↗
PubMed2003

Ventomod: a dynamic model for leaf to fruit transfer of radionuclides in processing tomato plants (Lycopersicon esculentum Mill.) following a direct contamination event.

This paper presents results on the calibration and validation of a model (Ventomod) for leaf to fruit transfer of (134)Cs, (85)Sr and (65)Zn in processing tomato plants after leaf contamination. Several models (e.g. FARMLAND) that deal specifically with the transfer of radionuclides to fruits are adaptations of models that were developed for agricultural crops such as leafy green vegetables. "Ventomod" represents a dynamic evaluation model exclusively built for the short-term behaviour of radionuclide depositions. It forecasts the level of radionuclide contamination in ripe processing tomato fruits following an accidental radionuclide release into the atmosphere. A validation of the developed model by data sets from an independent experiment showed that the model successfully reproduced the observed radionuclide distribution and dynamics in tomato fruits. The level of uncertainty was within the normal range of similar assessment models. For a more general use of this model further testing with independent data sets from experiments obtained under different environmental conditions and data from other horticulturally important plant species would be desirable.

Agriculture↗
PubMed2000

Bioavailability of zinc and its binding to casein in milks and formulas.

Differences in zinc bioavailability among milk and formulas may be attributed to binding of zinc to various ligands. We determined the distribution of zinc and protein at different pHs and zinc and calcium concentrations. We used radiolabelled cow's milk, human milk, whey-predominant (WPF) and casein-predominant (CPF) infant formula. Lowering the pH changed zinc and protein distribution: zinc shifted from pellet (casein) to whey in cow's milk, from fat to whey in human milk and from fat and pellet to whey in formulas. Protein shifted from whey to pellet in human milk and from whey and pellet to fat in formulas. Increasing zinc and calcium concentrations shifted protein and zinc from pellet to whey for cow's milk and from whey and pellet to fat for the formulas. Protein distribution was not affected by calcium or zinc addition in human milk or CPF, while zinc shifted from whey to fat in human milk and from fat and pellet to whey in CPF. Zinc and calcium binding to isolated bovine or human casein increased with pH. At 500 mg/L of zinc, bovine casein bound 32.0 +/- 1.8 and human casein 10.0 +/- 0.9 mg zinc/g protein. At 500 mg/L of calcium, calcium was preferentially bound over zinc. Adding calcium and zinc resulted in 32.0 +/- 1.8 mg zinc/g bound to bovine casein and 17.0 +/- 0.8 mg zinc/g to human casein, while calcium binding was low. Suckling rat pups dosed with 65Zn labelled infant diets were killed and individual tissues were gamma counted. Lower zinc bioavailability was found for bovine milk at pH = 4.0 (%65Zn in liver = 18.7+1.4) when compared to WPF (22.8 +/- 1.6) or human milk (26.9 +/- 0.8). Lowering the pH further decreased zinc bioavailability from human milk, but not from cow's milk or WPF. Knowledge of the compounds binding minerals and trace elements in infant formulas is essential for optimizing zinc bioavailability.

Animals↗
PubMed2003

Absorption of zinc from wheat products fortified with iron and either zinc sulfate or zinc oxide.

BACKGROUND: Several chemical forms of zinc have been proposed for food fortification, but information is needed on their absorption from common cereals having varied phytate content. OBJECTIVE: The goal was to measure zinc absorption from wheat products fortified with iron sulfate and either zinc sulfate or zinc oxide. DESIGN: Adult volunteers received either low-phytate bread (n = 11) or higher-phytate porridge (n = 11) once weekly on 2 or 3 occasions. The foods were fortified with 1 of the 2 zinc salts (60 mg elemental Zn/kg wheat flour) during week 1 and with the other during week 2, in random order. (65)Zn in the same chemical form as the fortificant was incorporated in each food to assess zinc absorption with the use of whole-body counting. The porridge group received an additional test meal fortified with zinc oxide during week 3, but the (65)Zn tracer was given as an oral solution of (65)ZnCl(2). RESULTS: Zinc absorption from bread (13.8%; 95% CI: 11.8%, 16.2%) was significantly (P < 0.001) greater than from porridge (6.4%; 5.5%, 7.6%), presumably because of the greater phytate content of the porridge. With control for food type, there were no significant differences in zinc absorption from meals fortified with zinc sulfate or zinc oxide (P = 0.24). When the porridge was fortified with zinc oxide and labeled with (65)ZnCl(2), absorption of the tracer (8.9%; 7.1%, 11.0%) was significantly (P = 0.007) greater than when (65)ZnO was incorporated in the porridge (5.6%; 4.5%, 6.9%). CONCLUSIONS: Either zinc oxide or zinc sulfate can be used to fortify wheat products consumed by presumably healthy persons. Isotopic tracers used to assess the absorption of mineral fortificants should have the same chemical form as the fortificant.

Adult↗
PubMed1999

Metallothionein-null mice absorb less Zn from an egg-white diet, but a similar amount from solutions, although with altered intertissue Zn distribution.

The influence of metallothionein (MT) on Zn transfer into non-gut tissues was investigated in MT-null (MT-/-) and normal (MT+/+) mice 4 h after oral gavage of aqueous 65ZnSO4solution at doses of 154, 385, 770 and 1540 nmol Zn per mouse. Zn transfer was not significantly different between MT+/+ and MT-/- mice and was directly proportional to the oral dose (slope = 0.127, r = 0.991; 0. 146, r = 0.994, respectively). Blood 65Zn and plasma Zn concentrations increased progressively in MT-/- mice at doses >154 nmol Zn, reaching levels of 2.4% of oral dose and 60 micromol/L, respectively, at the 1540 nmol Zn dose. The corresponding values for MT+/+ mice were approximately half, 1.0% and 29 micromol/L. Intergenotypic differences were found in tissue distribution of 65Zn within the body; MT-/- mice had higher 65Zn levels in muscle, skin, heart and brain, whereas MT+/+ mice retained progressively more Zn in the liver, in conjunction with a linear increase in hepatic MT up to the highest Zn dose. MT induction in the small intestine reached its maximum at an oral dose of 385 nmol Zn and did not differ at higher doses. Absorption of a 770 nmol 65Zn dose from a solid egg-white diet was only one fourth (MT+/+) and one eighth (MT-/-) of the Zn absorption from the same dose of 65Zn in aqueous solution. MT+/+ mice had greater (P < 0.05) Zn absorption from the egg-white diet than did MT-/- mice, indicating that gut MT confers an absorptive advantage, but only when Zn is incorporated into solid food.

Animals↗
PubMed2006

Bioavailability of zinc glycinate in comparison with zinc sulphate in the presence of dietary phytate in an animal model with Zn labelled rats.

The objective of this study was to quantify the bioavailability of zinc (Zn) from sulphate and glycinate as representatives of inorganic and organic zinc sources. The semi-synthetic basal diet contained 2 microg/g of native Zn and was fortified with pure sodium-phytate (8 g/kg) in order to simulate conditions of common cereal-based meals. The basal diet was supplemented with either 53 microg/g of Zn from sulphate (control) or 10 microg/g of Zn from either sulphate (ZnSulphate) or glycinate (ZnGly). Twenty-four (65)Zn-labelled, growing rats weighing 133 g were allotted to the three diets (eight animals per treatment) and were kept pair-fed to ZnSulphate for 15 days. Zn contents in blood plasma, femur and whole body, as well as, plasma alkaline phosphatase activities were reduced compared with control indicating a zinc deficiency in ZnSulphate and ZnGly treatment. This allowed their differentiation in zinc bioavailability. True absorption of dietary Zn was significantly higher in ZnGly than in ZnSulphate (51% vs. 44%) while losses of endogenous faecal Zn and urinary Zn were not affected to a quantitatively relevant extent (mean: 17% and 2% of intake). This resulted in a +30% significantly improved Zn retention for ZnGly (33% vs. 25%) and a lower severity on Zn deficiency symptoms compared with ZnSulphate. Metabolic utilization accounted for 95% of absorbed dietary Zn for both Zn sources. Overall, the bioavailability of zinc glycinate was significantly superior by 16% to zinc sulphate (49% vs. 42%), mainly because of a higher absorptive potential at presence of a strong anti-nutritive component (phytate) in the diet.

Animal Feed↗