Effect of amino acids on brain uptake of methyl mercury

Abstract

To investigate the effect of amino acids on the brain uptake of methyl mercury (MM), methyl mercury chloride (MMC), and some amino acids were injected iv to Wistar strain male rats (190 ± 10 g). One hour after the simultaneous injection of 10 μmol and 100 μmol l-cysteine ( l-Cys) to the rat, brain mercury content increased about three times as compared with that after a single injection of MMC alone. This effect of l-Cys was depressed by pre- and post-treatment with l-phenylalanine ( l-Phe), but not with l-lysine ( l-Lys) or l-glutamic acid ( l-Glu). BAL also increased the brain uptake of MM. However, l-Phe did not exert an effect on the increased brain uptake of MM. When 10 μmol MMC was injected to the rat treated with l-Phe or l-isoleucine ( l-Ile) (pre-, simultaneous, and post-treatment), brain mercury 2 hr after the injection was lower than that after the single injection of MMC. At that time, there was no significant difference in blood and plasma mercury concentrations between the l-Phe-treated and nontreated rats. Treatment with l-Lys and l-Glu did not affect the brain mercury content after MMC injection. Brain mercury after the injection of 10 μmol MMC increased with time. The rate of increase was lowered by pre-, simultaneous, and post-treatment with l-Phe for 2, 6, 9, and 12 hr. When l-Phe injection was started 12 hr after MMC injection and continued repeatedly for 12 hr, the brain mercury content was low when compared with that after the single injection of MMC. These data demonstrate that the brain uptake of MM is depressed by l-Phe and l-Ile, which are neutral amino acids, and not by l-Lys and l-Glu, which are a basic and an acidic amino acid, respectively.