Mercury 203 distribution in pregnant and nonpregnant rats following systemic infusions with thiol‐containing amino acids

Near‐term pregnant (gestational day 17) and nonpregnant Long‐Evans female rats were continuously infused into the external jugular vein with 0.1 mmole/hour L‐cysteine, 0.1 mmole/hour L‐leucine, or saline. At 24, 48, and 72 hours, 50 μmole/hour [²⁰³Hg]‐MeHgCl was administered over 1 hour. Total ²⁰³Hg body burden, brain, kidney, liver, and blood ²⁰³Hg concentrations were determined at 96 hours by gamma scintillation spectrometry. Despite significantly greater ²⁰³Hg whole body retention in the pregnant animals ²⁰³Hg concentrations in blood, brain, kidney, and liver were higher in nonpregnant rats. In addition, brain ²⁰³Hg concentrations in both pregnant and virgin rats were significantly higher in L‐cysteine‐treated rats compared with controls. These results suggest that the fetus may act as a “sink” for MeHg, thus decreasing ²⁰³Hg concentrations in maternal blood, brain, kidney, and liver. Furthermore, the data indicate that brain uptake of methylmercury in both pregnant and nonpregnant rats is enhanced by chronic L‐cysteine infusion, lending support to the hypothesis that methylmercury in the rat may be translocated across the blood‐brain barrier by the neutral amino acid carrier transport system.