塩化メチル水銀および亜セレン酸ナトリウム投与マウスにおける水銀とセレンの生体内分布

Abstract

It is widely known that the causative substance of “Minamata disease” was methylmercurials concentrated in the fishes and shellfishes. It has been also reported that the organs of the patients as well as those of cats, fishes and shellfishes which suffered from the same disease contained high concentrations of selenium in addition to methylmercurials.But the investigation of the modifying effect of selenium compounds on the toxicity of methyl-mercurials is not necessarily ample and the study on the distribution of methylmercurials and selenium compounds in the body exposed to them simultaneously is almost scanty. The present paper describes the distribution of radioactive mercury (203Hg) and selenium (75Se) in mice after the simultaneous exposure to methylmercuric chloride and sodium selenite.In order to determine radioactive mercury and selenium, the simultaneous-discriminative determination method using a Ge (Li) solid state detector with a multi-channel pulse height analyzer was established and used.Since the acute lethal dose of sodium selenite in mice have not yet been known, the lethal toxicity test was carried out in advance to fix the standard for the dose used in the present study. I. Lethal effective dose 50% (LD 50) of sodium selenite in mice.Thirty five mice (ICR-JCL strain, male, 12w., mean ±SE of body weight=37.0 ±2.3g) were equally divided into five groups. To each group of mice a single respective dose of 0, 3.0, 4.8, 7.7 and 12.3mg Se/kg of sodium selenite was injected subcutaneously. Observation period was one week. As a result the approximate value of LD 50 was 6 mg Se/kg and the dose-response curve seemed to rise sharply around LD 50.II. Simultaneous-discriminative determination method of radioactive mercury (203Hg) and selenium (75Se).The Ge (Li) solid state detector and the pulse height analyzer with 1024 channels were used for determining the radioactivity of 203Hg (γ : 0.279 MeV) and 75Se (γ : 0.280 and 0.265 MeV). The calibration curve of energy vs. channels, the relationship between the sample size and the cpm, the limits of determination and the percentage of the cpm of the γ-ray (0.280 MeV) to that of the γ-ray (0.265 MeV) of 75Se were examined. The method of calculation of the radioactivity from the record was also described.Consequently the samples of which both the radioactivity itself and the percentage of the cpm of the γ-ray (0.280 MeV) to that of the γ-ray (0.265 MeV) of 75Se showed the constant values with some variance and of which the sample size (cross section) was almost the same as that of the tissue used for the present experiment could be measured and gave us reasonable data. III. Distribution of 203Hg and 75Se in the body.Forty five mice (ICR-JCL strain, male, 11 w., mean ±SE of body weight=32.1±1.9g) were equally divided into three groups which were treated with methylmercuric chloride alone, both methylmercuric chloride and sodium selenite, and sodium selenite alone, respectively. To each group of mice labeled compounds of methylmercuric chloride (CH3203HgCl, 125 μCi/1mg Hg/1kg of body weight) and/or sodium selenite (Na275SeO3, 132 μCi/0.5mg Se/1kg of body weight) were injected subcutaneously. At the specified time mice were killed after collecting blood by heart puncture followed by removing the small intestines including their contents, brain, liver and kidneys. Radioactivity of mercury and selenium was measured according to the method described above.The results and discussion are as follows : 1. In regard to the concentration and the elimination rate of mercurials in the liver, kidneys, small intestines and blood, no obvious difference was detected between the group treated with the two compounds and the