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At least 19 recordsLinked to original sources
PubMed1989

Intrinsic and extrinsic stable isotopic zinc absorption by infants from formulas.

The kinetics of fecal elimination and the extent of fractional absorption of intrinsic and extrinsic zinc from infant formula were studied in 11 human infants by using a direct, simultaneous dual-label method based on fecal monitoring of unabsorbed stable isotope labels. The relative positions of the two stable isotopic tags (67Zn, 70Zn) as extrinsic and intrinsic labels were reversed in two separate determinations of fractional absorption. Administration of doubly labeled formula for 24 h or less permitted elimination of unabsorbed labels before the end of a 72-h metabolic interval. The extent of enrichment and the kinetics of fecal elimination of unabsorbed extrinsic stable isotopic zinc tag were observed to agree closely with the corresponding values for the intrinsic tag. Fractional absorption of intrinsic and extrinsic tags was highly correlated and did not differ significantly. The ratio of fractional absorption of extrinsic tag to that of intrinsic tag was 1.05 +/- 0.19 (mean +/- SD). The results constitute strong support for validation of the use of enriched stable isotopes at low levels (less than or equal to 10%) of extrinsic addition to milk-based diets for studies of zinc absorption by humans.

Analysis of Variance↗
PubMed1989

Radiochemical neutron activation analysis of zinc isotopes in human blood, urine, and feces for in vivo tracer experiments.

Enriched stable isotopes are being increasingly used for study of trace element nutrition in humans who cannot be studied by use of in vivo radioactive tracers (e.g., subjects under age 18 and pregnant women). Zinc metabolism in these subjects can be evaluated by administration of Zn enriched to 65% in the minor isotope, 70Zn (0.6% natural abundance). The enhanced 70Zn is detected later in red blood cells, plasma, urine, and feces by measuring 70Zn/64Zn or 70Zn/68Zn ratios. Stable isotope concentrations are measured by neutron activation of the samples and observation of their products: 244-day 65Zn, 14-h 69mZn, and 4-h 71mZn. Zinc-65 can be observed in these samples without chemical separations 3 weeks after irradiations, but large amounts of 24Na and other short-lived species preclude direct observation of the short-lived Zn activities. Preirradiation chemistry was developed to remove most interferences, the major steps being to place the sample on Chelex resin, elute alkali metals and alkaline earths from it, and irradiate the resin containing the Zn. gamma-Rays of 69mZn can be observed on the irradiated resin, but additional precipitation and solvent extraction steps are needed to remove 56Mn and 64Cu for clear observation of 71mZn and 65Zn within hours after irradiation. Yields for pre- and postirradiation separations are typically 85% and 70%, respectively. The stable isotope tracer method was validated by simultaneous in vivo tracing with radioactive 65Zn in four subjects.

Feces↗
PubMed1987

Intrinsic labeling of bovine milk with enriched stable isotopes of zinc.

Bovine milk was labeled intrinsically with enriched stable isotopic zinc for human bioavailability studies. Intrajugular administration of zinc isotopes temporarily increased the plasma zinc concentration of Ayrshire cows by as much as 76%, but milk zinc concentration and the distribution of zinc between casein and whey did not change appreciably. Milk zinc isotopic enrichment reached 105 and 613 atom % excess for 67Zn and 70Zn, respectively within 4-12 hr of zinc administration and decreased gradually over several days. This degree of isotopic enrichment is sufficient for testing bioavailability to infants of intrinsic zinc from milk-based formulas.

Animals↗
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↗
PubMedDate not supplied

Determination of isotope ratios in human tissues enriched with zinc stable isotope tracers using inductively coupled plasma-mass spectrometry (ICP-MS).

Enriched fecal and urine samples were prepared using ion-exchange column chromatography for analysis by Inductively Coupled and Fast Atom Bombardment Mass spectrometry (ICP-MS, FAB-MS) to compare precision between methods. Unenriched samples of human milk, feces, and whole blood were prepared similarly to monitor instrumental precision and analytical error. A least squares fit of the ICP-MS results vs the FAB-MS for 70Zn/64Zn gave a slope of 0.98, with a relative standard deviation (RSD) of only 0.7%. The results for 68Zn/64Zn gave a slope of 0.82, with a RSD of 14%. For unenriched tissues, all potential interferences were removed by the preparation procedure with no significant differences between preparation for isotope ratios of 70Zn/64Zn, 68Zn/64Zn, 67Zn/64Zn, and 66Zn/64Zn. Poisson counting statistics are a major contribution to the total analytical error indicating the usefulness of this procedure for enrichment studies.

Animals↗
PubMed1981

Intrinsic labelling of chicken meat with stable isotopes of zinc, for intended use in human feeding studies: feasibility and design considerations.

1. The feasibility of intrinsically labelling poultry meat with the stable isotopes 68Zn and 70Zn was investigated. 2. Chickens (1-d-old) were gavaged with solutions of 68Zn and 70Zn several times over a 42 d period. 3. Isotopic analysis of edible tissues has shown that they were significantly enriched with respect to the gavaged isotope and that the extent of isotopic enrichment achieved was sufficient to permit their use in human feeding experiments designed to investigate availability of native Zn from such food models. 4. The absolute efficiency of retention of the stable isotopes from gavage solutions in the edible tissues has been calculated to be 2-3% of the administered dose; methods have been suggested to enhance this value, based on considerations of utilization of dietary Zn.

Animals↗
PubMed1991

Intrinsic labelling of different foods with stable isotope of zinc (67Zn) for use in bioavailability studies.

Intrinsically-labelled foods are required to validate extrinsic-labelling techniques used to study the bioavailability of trace elements. Wheat (Triticum aestivum), peas (Pisum sativum), goat's milk, human milk, eggs and chicken meat were selected for intrinsic-labelling studies with 67Zn. Peas were grown hydroponically in enriched nutrient solution and wheat was grown in sand and watered with enriched nutrient solution. Some of the wheat plants were also given stem injections of 67Zn solution. Eggs and chicken meat were prepared by administering 67Zn intravenously to chickens, and human milk was collected after an oral dose of 67Zn in a cola drink. All the foods investigated were sufficiently enriched with 67Zn for Zn absorption studies except wheat prepared by the sand and water-culture method.

Animals↗
PubMed1989

Effect of low zinc intake on absorption and excretion of zinc by infants studied with 70Zn as extrinsic tag.

The effect of low dietary intake of zinc was studied in six normal infants with the use of 70Zn as an extrinsic tag. Of the two study formulas, one provided a zinc intake similar to that of customary infant formulas ("high" intake), whereas the other provided a "low" zinc intake. Two zinc absorption studies were performed with each formula (sequence: high-low-low-high). Extrinsically labeled formula was fed for 24 h and excreta were collected for 72 h. Zinc isotope ratios were determined by inductively coupled plasma mass spectrometry (ICP/MS). When zinc intake was high, net zinc absorption was 9.1 +/- 8.7% (mean +/- SD) of intake and net zinc retention was 74 +/- 91 micrograms/(kg.d). True zinc (70Zn) absorption was 16.8 +/- 5.8% of intake and fecal excretion of endogenous zinc was 78 +/- 56 micrograms/(kg.d). When zinc intake was low, net absorption of zinc increased significantly (P less than 0.001) to 26.0 +/- 13.0% of intake, but net retention was not significantly different at 42 +/- 33 micrograms/(kg.d). True absorption of zinc also increased significantly (P less than 0.001) to 41.1 +/- 7.8% of intake, whereas fecal endogenous zinc decreased (P less than 0.05) to 34 +/- 16 micrograms/(kg.d) during low zinc intake. Thus, infants maintain zinc balance in the face of low zinc intake through increased efficiency of absorption and decreased excretion of endogenous zinc.

Adaptation, Physiological↗
PubMed1986

Stable isotope studies of zinc absorption and retention in young and elderly men.

Zinc absorption was determined with 67Zn and 70Zn, stable isotopes of zinc, in six young men and six elderly men who were confined to a metabolic unit for 12 wk. Their purified formula diets, supplemented with select food items, contained 15 mg of zinc per day. Zinc absorption was determined twice for each subject by combining zinc enriched with either 70Zn or 67Zn with the formula diet. Serum, urinary, and fecal zinc and zinc balance were determined by atomic absorption spectrometry. Zinc absorption averaged 17% in elderly men, significantly less than average zinc absorption of 31% in young men. Serum zinc was also lower in elderly men and increased in both groups during the course of the study. Zinc balance did not differ between groups, and endogenous zinc losses were less in the elderly than in the young men. The results suggest that while zinc absorption is less in elderly men than in young men, the lower absorption may reflect a lower requirement for absorbed zinc by the elderly. Alternatively, less efficient zinc absorption could result in decreased endogenous losses.

Absorption↗
PubMed1984

A stable isotope study of zinc absorption in young men: effects of phytate and alpha-cellulose.

A 63-day study was conducted with young men confined to a metabolic unit to study the effects of a alpha-cellulose and phytate on zinc absorption. A liquid formula diet was used throughout the experiment. During each of three dietary treatments, (basal diet, basal diet + alpha-cellulose, or basal diet + phytate), 67Zn, a stable isotope of zinc, was added to the diets to measure zinc absorption. Zinc absorption was determined by fecal monitoring of 67Zn, measured by thermal ionization mass spectrometry. Analytical precision of all measurements was within 1%. Average zinc absorption was 34.0 +/- 6.2% from the basal diet and 33.8 +/- 2.9% from the diet with 0.5 g alpha-cellulose per kg body weight added. Zinc absorption fell to 17.5 +/- 2.5% when 2.34 g of phytate as sodium phytate were added to the basal diet. The phytate/zinc molar ratio of the diet was 15. The decrease in zinc absorption was accompanied by increased fecal zinc and decreased urinary zinc. The results suggest that phytate inhibits zinc absorption and high levels of dietary phytate could result in zinc deficiency in man.

Absorption↗
PubMed1985

Placental handling of zinc in the guinea pig.

The distribution of zinc between the mother and the fetoplacental unit, and its placental transfer, were studied using stable and isotopic zinc in unanaesthetized pregnant guinea pigs and an in situ perfusion preparation. The concentration of stable zinc in fetal plasma and skeletal muscle was higher than that in the maternal tissues: 2.0 compared with 1.4 micrograms/ml and 84 with 49 ng/mg dry weight, respectively. The placenta and maternal and fetal liver had similar zinc concentrations: 90, 75 and 88 ng/mg dry weight, respectively. The ability of the placenta to concentrate 65Zn, measured 1 h after a single intravenous injection into the unanaesthetized mother, was comparable with that of the maternal liver. Maternal-fetal mass transfer of zinc was directly related to maternal plasma zinc concentrations from 0.7 to 24.1 micrograms/ml (b = 2 ng X min-1 X g-1 X microgram-1, r = 0.92). At physiological plasma levels, the calculated transfer would supply the fetus with 0.12 mg zinc/day, similar to the accretion rate over the last trimester. Placental transfer of zinc was not influenced by the concentration of zinc in the placental perfusate. Extraction of zinc from the perfusate was also slow, and partly by absorption. Maternofetal transfer of zinc was directly related to both uterine and umbilical blood flows. The high concentration of zinc in the syncytium, relative to both maternal and fetal plasma levels, suggests active uptake at the maternal surface, combined with a slow release into the fetus, down a concentration gradient.

Animals↗
PubMed1989

Zinc absorption and achlorhydria.

Zinc absorption from 40 mumol of zinc in a water solution and from a test meal containing 22 mumol of zinc was studied in 8 patients with achlorhydria (no basal acid secretion and no secretion after pentagastrin stimulation). The test dose and the meal was labelled with 0.1 MBq of 65Zn and absorption was determined from measurement of the whole-body retention of the isotope. Zinc absorption was 68 +/- 16 per cent (mean +/- s.d.) from the water solution and 33 +/- 10 per cent from the test meal. The results did not differ from absorption in control subjects and indicate that achlorhydria per se does not affect zinc absorption.

Achlorhydria↗
PubMed1982

Use of enriched stable isotopes to determine zinc and iron absorption in elderly men.

The absorption of zinc and iron was determined in seven elderly men using the enriched stable isotopes 70Zn and 58Fe. Analyses of isotopic ratios were done using thermal ionization magnetic sector mass spectrometry on chloride solutions of zinc and of iron after separation of zinc from fecal samples by ion exchange and of iron by solvent extraction. Mean apparent zinc absorption in the seven subjects was 17.3 +/- 3.1% (mean +/- SEM) and mean iron absorption was 7.9 +/- 2.5% (mean +/- SEM) when fed a semipurified diet containing 15 mg of zinc and 10 mg of iron daily. Quantities absorbed were equivalent to an average of 2.6 mg of zinc and 0.8 mg of iron per day. These average zinc and iron values are close to previous estimates of endogenous losses of zinc and iron.

Absorption↗