The TSH-dependent variation of the essential elements iodine, selenium and zinc within human thyroid tissues.

Instrumental Neutron Activation Analysis was used in order to measure iodine, selenium and zinc concentration in thyroid samples. A pair of samples of normal and nodular tissue were collected from the thyroid gland from 72 patients selected on the basis of pathological criteria (44 cases of multinodular goiter, 12 of chronic lymphocytic thyroiditis (CLT), 6 of thyroid adenoma (TA) and 12 of thyroid cancer (TC)). The check for tissue homogeneity and sampling error was performed by means of the coefficient of variation (CV%) of the elements in replicate samples of normal and altered tissues. High CV% values (> 15%) for iodine reflected a functional variability in thyroid follicles, while low CV% values (< 10%) for selenium and zinc indicated that the composition of selected tissues was rather homogeneous. The variation of the element's concentration was compared in normal and altered tissues. The mean element concentrations had values close to those already reported in the literature; furthermore, our patients had marginal iodine and selenium deficiency. Both normal and nodular tissues in CLT showed statistically significant lower zinc values as compared with the other thyroid diseases. To evaluate the thyroid function, thyroid stimulating hormone (TSH) and thyroxine (T4) levels were measured in the serum of patients. Two arbitrary serum-TSH threshold levels (TSH < 1.0 and > 4.0 mU/L) were introduced in order to classify, respectively, hyperthyroidism and hypothyroidism, as well as euthyroid conditions (1.0 < TSH < 4.0 mU/L), and each patient was assigned to one of these groups. The influence of TSH in the variation of the concentration of iodine, selenium and zinc in normal and altered human thyroid tissues was significant.

Speciation as an analytical aid in trace element research in infant nutrition.

The aim of this work was twofold: to study the binding pattern of trace elements in formulas as compared with breast milk and the relationship between trace elements in breast milk and in maternal dietary intake. To investigate the binding form of trace elements in these nutritive fluids, methods for protein separation were combined with methods for trace element determination in the eluted fractions. HPLC and ICP-AES or ICP-MS were coupled on-line for the simultaneous speciation of elements of nutritional interest, viz., Ca, K, Mg, P, S, Co, Cu, Fe, I, Mn, Mo, Se and Zn, and also the heavy metals Cd and Pb in both human mild whey and formulas. In order to minimize interactions between the labile metal protein complexes and the column material, size-exclusion chromatography was used for protein separation. The binding pattern of trace elements in formulas is significantly different from that in breast milk and depends on its main component (cow's milk or soy), its processing (hydrolysis) and the chemical form (inorganic) of the added compounds. For example, compared with breast-fed infants the iron supply of formula-fed infants is much higher (up to 20-fold); in addition, the binding forms of Fe are very different in the two fluids. This has to be evaluated with respect to interactions with other elements during intestinal uptake. The investigation of breast milk samples from different regions of the world showed comparable shapes for teh elution profiles and for Mo and Se a dependence on the regional maternal dietary intake. Speciation studies carried out on breast milk samples as a function of the selenium content showed significant changes in the zinc-binding pattern. In particular, citrate (as a zinc-binding component) was found to decrease with increasing dietary selenium intake of the mother.

Influence of high dietary selenium intake on the thyroid hormone level in human serum.

Effects of high dietary selenium supply (range 170-980 micrograms per day) on the metabolism of thyroid hormones were studied in serum of mothers living in seleniferous areas of Venezuela. Free thyroxine (FT4), free triiodothyronine (FT3) and human thyroid stimulating hormone (hTSH) were found to be within the normal range but a significant inverse correlation was found between the FT3 and selenium. It was hypothesized that the activity of hepatic selenoenzyme type I iodothyronine 5'-deiodinase, which catalyzes the production of T3 from T4, becomes depressed at high levels of dietary intake of selenium. The effect is discussed with respect to the safe level of dietary selenium intake, which was estimated to be below 500 micrograms per day.

Selenium status of children living in seleniferous areas of Venezuela.

Selenium was measured in red blood cells, serum and hair of children and in breast milk of mothers in seleniferous areas of Venezuela by means of neutron activation analysis. Signs of selenosis were observed only in a few cases. Reduction in the rate of growth is discussed with respect to unequal local nutritional conditions during the growth period.

An automated microtechnique for selenium determination in human body fluids by flow injection hydride atomic absorption spectrometry (FI-HAAS).

The automation of a flow injection system for the hydride generation of selenium and its subsequent determination by atomic absorption spectrometry (FI-HAAS) is described. Pre-treatment of the sample and the details of the automated equipment are reviewed. For the FI-HAAS selenium analysis a volume of 350 microL of acid-digested sample solution is injected. The on-line generated hydride is delivery by the gas-liquid separator and is transported together with an Ar stream to the heated quartz cell for the atomic absorption determination. The absolute detection limit is 35 pg Se; the relative detection limit 0.10 micrograms/L Se. The absolute determination limit in real biological samples is 110 pg Se; the relative detection limit 0.31 micrograms/L Se. The accuracy of the method was evaluated via analysis of certified standard reference materials. Quality control was made by comparing FI-HAAS and instrumental neutron activation analysis (INAA), as an independent analytical method. Two acid-digestion procedures (in open vessels at atmospheric pressure and bomb-digestion in pressure vessels) were experimentally tested. To determine the effectiveness of the selenium reduction and the completeness of the selenium hydride formation a parallel selenium determination was carried out by means of ICP-AES and FI-HAAS analysis. FI-HAAS was applied for blood serum analysis of children undergoing long-term total parenteral nutrition, as well as of persons with high dietary selenium intake, and for human milk analysis.