Sex Difference in the Influence of Dietary Protein Deficiency on the Fate of Methylmercury in Mice and Rats

2006

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The effects of L-methionine (Met) on tissue distribution of methylmercury (MeHg) in mice were investigated and compared to those of other amino acids and amino acid analogues to determine whether Met could play special roles in distribution of MeHg. Three hr after the injection with MeHg-L-cysteine (Cys) (10 mol/kg each), brain Hg concentration was suppressed by a co-injection with Met, L-phenylalanine (Phe), L-leucine (Leu) or 2-amino-2-norbornanecarboxylic acid (BCH), although the concentration was not affected by that with L-serine, ␣-aminoisobutyric acid or ␣-(methylamino)isobutyric acid. Hg concentration in liver was enhanced but that in the kidney was suppressed only by the co-injection with Met. Hg concentrations in blood and plasma were suppressed only by Met at least within 2 hr, but these differences disappeared at 3 hr. These results suggest that Met plays important and special roles in tissue distribution of MeHg in mice, at least in the liver and kidney, although MeHg distribution in the brain is similarly affected by not only Met but also other compounds such as Phe, Leu and BCH.

Section: Discussionmentioning

confidence: 99%

Characteristic Effects of L-Methionine on Tissue Distribution of Methylmercury in Mice

2006

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“…6,7,10,31) In addition, the percentage of Hg accumulated in the brain to Hg administered was also higher in LPD-fed mice due to similar body and brain weights. 31) However, no difference was observed in the brain Hg concentration between the dietary groups in rats (Fig. 1).…”

Section: Discussionmentioning

confidence: 91%

“…4D) by dietary protein deficiency. The decrease in urinary Hg excretion by the lowered dietary protein level is also observed in not only male mice 6,7,10) but also in female animals 31) despite the marked sex difference in the fate of MeHg in intact animals, 3,4) suggesting that this decrease would be universally caused by dietary protein deficiency. It has been suggested that urinary excretion of MeHg is regulated by many processes according to the following mechanism.…”

Section: Discussionmentioning

confidence: 93%

Influence of Dietary Protein Levels on the Fate of Methylmercury and on Amino Acid Transport at the Renal Brush Border Membrane in Rats

Hirayama

2005

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We investigated the influence of dietary protein levels on the fate of methylmercury (MeHg) in rats, and the difference in its urinary excretion was discussed from the viewpoint of the dietary protein level-dependent alteration in activity of the neutral amino acid transport system, through which MeHg metabolites such as MeHg-L-cysteine are reabsorbed, at the renal brush border membrane. When MeHg was administered to rats fed either a 24.8% protein diet (normal protein diet, NPD) or a 7.5% protein diet (low protein diet, LPD), urinary Hg excretion was much lower in LPD-fed rats than in NPD-fed rats, whereas no difference was observed in fecal excretion 1 day after MeHg administration. At that time, Hg concentrations in the brain and plasma were similar in the two dietary groups, whereas the concentrations in liver and blood were higher, but the renal concentration was lower in LPD-fed rats than in NPD-fed rats. Regardless of the presence of Na + , uptake of 14 C-L-phenylalanine for the first 20 sec was higher in the renal brush border vehicles from LPD-fed rats than in those from NPD-fed rats. These results suggest that dietary protein deficiency enhances the neutral amino acid transport at the renal brush border membrane, which could lead efficient reabsorption of MeHg metabolites from the proximal luminal space, and it might play a key role in the marked decrease in urinary excretion of MeHg.

“…We recently revealed that, regardless of the marked sex difference in the fate of MeHg in intact C57BL mice, [11][12][13] its fate was similarly affected by a dietary modification (dietary protein deficiency) regardless of sex, except for the gonads. 14) We, therefore, suggested that some factors that affect the fate of MeHg might be similarly influenced by this dietary modification both in males and females.…”

Section: Fig 1 Time-dependent Changes In Tissue and Excreted Hg In mentioning

confidence: 88%

Differences in the Fate of Methylmercury between Mice with and without Hair

Kuwana

2006

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We investigated time-dependent changes in the fate of methylmercury (MeHg) in both sexes of hairy and hairless mice during 6 days after its single administration to clarify whether the presence of hair could affect tissue distribution and excretion of MeHg. Despite the excretion of mercury (Hg) into hair of hairy mice, Hg concentrations in several but not all tissues were higher in hairy than in hairless mice, especially in the brain, liver, kidney and testes in males and in the brain, liver and blood in females. The cumulative amounts of Hg excreted in feces in males and in both urine and feces in females were lower in hairy than in hairless mice, whereas there was no significant difference in the urinary level in males. However, significant differences in the tissue Hg levels were observed earlier than those in the excretory Hg levels. Accordingly, the higher Hg levels in various tissues of hairy mice as compared to those in hairless mice would not have resulted from the lower Hg excretion levels. These results suggest that the presence or absence of hair markedly affects the fate of MeHg, but the differences in its fate between hairy and hairless mice would not be directly due to the fact that hair provides an excretion route.