Brain, Kidney and Liver ²⁰³Hg‐Methyl Mercury Uptake in the Rat: Relationship to the Neutral Amino Acid Carrier

Abstract: To investigate the effect of L‐neutral amino acids on tissue levels of methyl mercury in the adult animal, rats were infused into the external jugular vein with solutions containing a) 0.05 mM ²⁰³Hg‐MeHgCl and saline, b) 0.05 mM ²⁰³Hg‐MgHgCl‐0.1 mM L‐cysteine, c) 0.05 mM ²⁰³Hg‐MeHgCl‐0.1 mM L‐cysteine‐0.1 mM L‐methionine, d) 0.05 mM ²⁰³Hg‐MeHgCl‐0.1 mM L‐leucine, or e) 0.05 mM ²⁰³Hg‐MeHgCl‐0.1 mM L‐cysteine‐0.1 mM L‐leucine. Groups of animals were sacrificed at 3 min. 7 hr, and 96 hr. Brain, kidney, and liver ²⁰³Hg radioactivity was measured by means of gamma‐scintillation spectrometry. Brain ²⁰³Hg concentrations L‐cysteine treated animals were significantly higher compared with saline treated animals (P<0.05) at 3 min., 7 hr and 96 hr. The coinjection or coinfusion of methyl mercury with L‐cysteine and L‐methionine abolished the L‐cysteine‐mediated brain ²⁰³Hg uptake (P<0.05), at each sacrifice time. Kidney and liver ²⁰³Hg concentrations were not significantly different in any of the treatment groups compared with controls, irrespective of the sacrifice time. Furthermore, the percentage of diffusible ²⁰³Hg (non‐protein bound) at each sacrifice time was not statistically different irrespective of the treatment assigned. These results suggest that methyl mercury L‐cysteine conjugates in the plasma may share a common transport step with the L‐neutral amino acid carrier transport system and indicate the presence in brain capillaries of a transport system capable of selectively mediating methyl mercury uptake across the capillary endothelial cell membrane. 1989 Nordic Pharmacological Society