Study on proportional effect of life span exposure of air pollutant (NO_2) on respiratory tumor carcinogenesis.

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The effects of nitrogen dioxide (NO_2) on lung tumorigenesis by N-bis(2-hydroxypropyl) nitrosamine (DHPN) in male Wistar rats Were investigated. Rats were injected with o.5 g DHPN per kg body weight or saline intraperitoneally one time at 6 weeks of age, and then exposed to clean air, 0.04 ppm or 4 ppm NO for 17 months. Incidence of tumor in lungs of rats in DHPN + 4 ppm NO_2, group was 13%, and the tumors were adenoma and adenocarcinoma.Adenoma was seen in 4 of 40 rats (10%) and adenocarcinoma was seen in I of 40 rats (3%).The incidence of tumor in lungs of rats in DHPN + clean air and DHPN + 0.04 ppm NO_2 groups was only 3% (1/40), respectively. The tumors were adenoma. There was no significant difference in the incidence of tumors between DHPN + clean air group and DHPN + 4 ppm NO_2 group. No lung tumor was seen in DHPN + 0.4 ppm group and each NO_2-exposed group without DHPN treatment. Alveolar cell hyperplasia occurred at the highest incidence in.lungs of rats injected with DHPN. But, there was no any correlation between the incidence of hyperplasia and each concentration of NO_2 exposed. Bronchiole mucosal hyperplasia was seen in 17 of rats (43%) in the DHPN + 4 ppm NO_2 group, and in I of 40 rats (3%) in the each clean air, 0.04 ppm or 0.4 ppm NO_2 exposed-groups with DHPN treatment. The hyper- plasia in lungs of rats exposed to 4 ppm NO_2 without DHPN treatment was more slighter than that seen in the 4 ppm NO_2-exposed group with DHPN treatment.These results indicate that development of lung tumors in rats injected with subcarcino- genic dose of DHPN was-enhanced by exposure to 4 ppm NO_2. However, low levels of NO_2 effect on lung tumor development was not observed in Wistar rats.