Determination of metallothionein levels in tissues of young rats fed zinc-enriched diets

Effects of Dietary Zinc on Growth, Haematological Indices, Digestive Enzyme Activity, Tissue Mineralization, Antioxidant and Immune Status of Fingerling Heteropneustes fossilis

A 12 week feeding trial was conducted to evaluate the effects of dietary zinc levels on Heteropneustes fossilis. Triplicate groups of fish were fed isoproteic (CP; 400 g/kg) and isocaloric (GE; 17.89 kJ/g) diets increasing levels of zinc (0, 5, 10, 15, 20, 25, 30 mg/kg) achieved by supplementing zinc sulphate heptahydrate to basal diet. Analysed concentrations of zinc in diets were 10.68, 15.83, 21.34, 26.74, 30.61, 34.91 and 41.34 mg/kg. Growth indices increased linearly (P<0.05) up to 26.74 mg/kg Zn. The protein and ash content of whole body also improved significantly up to 26.74 mg/kg Zn. Whole body fat content showed inverse pattern. Haematological parameters also showed an improving trend with the increase in dietary zinc up to 26.74 mg/kg and then levelled off. Activities of antioxidant enzymes were improved with the increase in dietary zinc level up to 26.74 mg/kg followed by no significant change (P>0.05). Serum lysozyme activity also exhibited the similar pattern. Immune response in terms of the activities of lysozyme, alkaline phosphatase and myeloperoxidase was also improved with the increase in dietary zinc levels up to 26.74 mg/kg. Dietary zinc levels affected significantly the whole body as well as vertebrae mineralization. Broken-line regression analysis of weight gain, vertebrae zinc activity, serum superoxide dismutase and protease activity against increasing amounts of dietary zinc revealed that the inclusion of zinc in diet in the range of 26.82-29.84 mg/kg is optimum for growth, haematological indices, antioxidant status, immune response and tissue mineralization in fingerling H. fossilis. The information obtained from present study would be helpful in formulating the zinc-balanced commercial feeds to improve the growth and health status of this important fish, thus contributing to aquaculture production and strengthening the food security.

Co-administration of Selenium with Inorganic Mercury Alters the Disposition of Mercuric Ions in Rats

Mercury (Hg) is a common environmental toxicant to which humans are exposed regularly through occupational and dietary means. Although selenium supplementation has been reported to prevent the toxic effects of Hg in animals, the mechanisms for this prevention are not well understood. The purpose of the current study was to determine the effects of selenium on the disposition and toxicity of Hg. Wistar rats were injected intravenously with a non-nephrotoxic dose (0.5 μmol kg^-1) or a nephrotoxic dose (2.5 μmol kg^-1) of HgCl₂ (containing radioactive Hg) with or without co-administration of sodium selenite (Na₂SeO₃). Twenty-four hours after exposure, rats were euthanized, and organs were harvested. Co-administration of SeO₃^2- with HgCl₂ reduced the renal burden of Hg and the urinary excretion of Hg while increasing the amount of Hg in blood and spleen. We propose that Hg reacts with reduced selenite in the blood to form large Hg-Se complexes that are unable to be filtered at the glomerulus. Consequently, these complexes remain in the blood and are able to accumulate in blood-rich organs. These complexes, which may have fewer toxic effects than other species of Hg, may be eliminated slowly over the course of weeks to months.

Aspectos recentes da absorção e biodisponibilidade do zinco e suas correlações com a fisiologia da isoforma testicular da Enzima Conversora de Angiotensina

A associação estável a macromoléculas e a flexibilidade da esfera de coordenação são propriedades intrínsecas do zinco e sua essencialidade encontra-se intimamente relacionada ao seu papel biológico, seja na ativação da função catalítica de enzimas, seja na estabilização das estruturas conformacionais de proteínas e ácidos nucléicos. O zinco é o segundo elemento traço essencial mais abundante no organismo humano e é necessário à atividade de mais de 300 enzimas dos 6 tipos de classes existentes. Estas características tornaram o metal e seus ligantes fontes de grande interesse para a nutrição experimental, já que o seu estudo converge para a determinação da biodisponibilidade do metal. Dentre esses ligantes, a isoforma testicular da Enzima Conversora de Angiotensina, sintetizada pelas células germinais masculinas, pode ser considerada um exemplo marcante de regulação molecular a partir da ligação do zinco, influenciando tanto a atividade quanto a concentração desta enzima e conseqüentemente a função testicular.