The objective of this work was to quantify metallothioneins (MT's) in tissues of rats fed different concentrations of zinc, in order to observe the animal response to the metal in relation to different types of diets, and to assess the nutritional status relating to zinc in the diets. Thirty-two Wistar newly-weaned male rats were distributed into four experimental groups and housed in individual cages. They had free access to water and diet containing different zinc concentrations, named RC (AIN 93-like diet), RH (customary diet of the university restaurant), both non-supplemented, and RCS and RHS, supplemented. After four weeks, the animals were killed and liver, kidneys, femurs and testes were isolated to determine metallothionein levels by a Cd/Hb affinity assay. Zinc content was determined by Flame Atomic Absorption Spectroscopy (FAAS). The results showed that zinc supplementation produced no change in the tissue metallothionein profile in the doses under analysis. The highest metallothionein mean concentration was found in the liver - 36.21 ± 0.88 µg/g (mean for RC-RCS groups), and 28.92 ± 5.32 µg/g (mean for RH-RHS groups). Metallothionein concentrations in testes were quite high, considering the small volume of the organ - 19.29 ± 0.54 µg/g (mean for RC-RCS groups), and 17.22 ± 1.07 µg/g (mean for RH-RHS groups). Significant increases in zinc concentration were observed in the liver of young supplemented rats - 38.94 ± 3.43 µg/g of tissue for RCS, and 42.83 ± 2.78 µg/g of tissue for RHS, and in the femurs - 140.04 ± 6.03 µg/g of tissue for RCS, and 86.57 ± 6.95 µg/g of tissue for RHS. The different carrying zinc food matrices caused no change in the adaptive response to metallothionein metabolism, and the lack of responsiveness towards metallothionein synthesis did not invalidate the results of tissue zinc concentration parameters, which suggest different degrees for zinc bioavailability.
metallothionein; zinc; biological availability; experimental diets
