The dynamic pathway of inhaled nitrogen dioxide was investigated in rats exposed to ¹⁵NO₂ for the specified experimental period. After exposure, various organs, blood and urine were taken out, dried by lyophilization, and then digested by the semi-micro Kjeldahl method. Determination of ¹⁵N was performed by mass-spectrometry. The ¹⁵N content (atom % excess) of each sample was calculated by subtracting the natural ¹⁵N content which was separately estimated from normal rats. The ¹⁵N content was relatively high in urine, plasma and kidneys, and low in liver, trachea, heart and brain. It was concluded that the inhaled nitrogen dioxide was quickly absorbed into blood and was excreted into urine. Nitrite was detected in the plasma obtained from the rats exposed to ¹⁵NO₂ at levels higher than 10 ppm, and a significant correlation was found between the concentration of nitrite and the exposure concentration of ¹⁵NO₂.

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Effects of physical loads on the excretion of urinary glycine conjugates, which are commonly used as an index of organic solvent intake, were examined. After physical exertion by Kendo exercise in university students for about 2 hours, urinary protein excretion changed from the levels of (-) or (+) before the exercise to (+) or (〓) after the exercise revealed by the test-tape semi-quantitative indication, and the levels of urinary creatinine increased to approximately 1.9 time the initial level. Under the present experimental conditions, the following results were obtained. 1) Statistically no significant change was observed in the levels of urinary hippuric acid, but an increasing trend was recognized. 2) The glycine levels in the urine decreased and the significance was stressed when the values were adjusted with reference to the specific gravity of urine or to the levels of urinary creatinine. 3) The ratio of hippuric acid to the glycine in the urine increased almost twice as high as the initial ratio and the physical load seemed to promote the glycine conjugation. 4) As to the adjusted levels of urinary metabolites, especially due to several organic solvents, values adjusted with reference to the specific gravity of urine and those to the levels of urinary creatinine correlated well in the samples collected before the exertion. But a poor correlation was observed in the samples collected after the exertion. Therefore, a notice should be given when the adjustment of the values with reference to the levels of urinary creatinine, which is widely used in the health administration practice for organic solvent workers to assess the levels of exposure, since the adjusted values were lowered unnecessarily by excess excretion of creatinine after the physical exertion and the tendency would be exaggerated especially under the low level exposure to organic solvent vapours in the work yard.

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Styrene is known to have an irritating effect on the tracheal mucosa, but there are few reports that have demonstrated it histologically. We carried out styrene-exposure experiments on rats, and made observations on morphological changes of the trachea with an electron-microscope. Observations on its functional aspects were also made by estimation of the cilliary movement per minute. The present study has revealed a considerable damaging effect of styrene on the tracheal mucosa, which we have presented in this report in the hope that it could be used as an index in settling the maximum permissible concentration of styrene for the future.

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The toxicity of tetrahydrofuran (THF), an important solvent in chemical industries, was studied by experiments on mice and rats. Acute toxicity was studied by intraperitoneally injecting 20% THF solution in various doses and by causing THF of various concentrations to be inhaled. Toxic symptoms appearing during the experimental period were observed. The results are as follows: 1. Acute toxic dose of THF. LD₅₀ was estimated to be 2, 500 mg/kg in mice with intraperitoneal administration of 20% THF-olive oil solution and 1, 900 mg/kg in mice and 2, 900 mg/kg in rats with intraperitoneal administration of 20% THF-0.9% NaCl solution. LC₅₀ was estimated to be 21, 000 ppm in rats when THF was inhaled for three hours. 2. Acute toxicity by inhalation of THF for three hours. Rats exposed to 100 to 200 ppm of THF showed no significant effects, except for slight local irritant symptoms such as redness of the nose and eyelids. Almost all rats exposed to over 5, 000 ppm of THF displayed marked local irritant symptoms such as edema or opacity of the cornea, salivation and discharge or bleeding in nasal mucosa. A cataleptoid posture, coma and clonic muscle spasms indicating irritant symptoms of the central nervous system were also observed.

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The toxicity of tetrahydrofuran (THF) was evaluated by repeated inhalation experiments on rats. The animals were separated into a control group and groups exposed to 100, 200, 1, 000 or 5, 000 ppm THF for 4 hours a day, 5 days a week over a 12-week period. No significant differences appeared between the groups exposed to 100 ppm as well as 200 ppm and the control group, except for slight local irritant symptoms of the mucosa. The group exposed to 1, 000 ppm showed an effect on the liver function according to the results by serum chemistry test. In the group exposed to 5, 000 ppm, marked local irritant symptoms and morphological damage of the respiratory mucous membrane were found upon histological examinations. Also significant differences were noted between this group and the control group in white blood cell counts, blood sugar values and liver functions by hematological and serum chemistry tests.

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