Comparative tumorigenicity of 1-nitropyrene, 1-nitrosopyrene, and 1-aminopyrene administered by gavage to Sprague-Dawley rats.

The carcinogenic activities of 1-nitropyrene, a mutagenic component of diesel exhaust, and its reduced derivatives 1-nitrosopyrene and 1-aminopyrene were evaluated in male and female Sprague-Dawley rats. Within 24 h of birth, groups of 22-36 rats were treated by gavage with trioctanoin or the appropriate compound in trioctanoin once weekly for 16 weeks. The approximate total doses per rat were as follows: 1-nitropyrene, high dose (800 mumol); 1-nitropyrene, low dose (320 mumol); 1-nitrosopyrene (320 mumol); 1-aminopyrene (320 mumol). The experiment was terminated after 94 weeks. The main site of tumor induction was the mammary glands of female rats. Percentages of incidences of mammary adenocarcinomas in female rats were as follows: 1-nitropyrene, high dose (63%); 1-nitropyrene, low dose (42%); 1-nitrosopyrene (19%); 1-aminopyrene (4%) trioctanoin (3%). These incidences were significantly greater than those of controls for the female rats treated with either 1-nitropyrene or 1-nitrosopyrene. Low and generally insignificant incidences of tumors of a variety of other sites were also observed in rats treated with 1-nitropyrene. The induction of mammary tumors by 1-nitropyrene confirms the results of a previous study (Hirose et al., Cancer Res., 44: 1158-1162, 1984). The present results also demonstrate that, under the conditions of this bioassay, 1-nitropyrene was significantly more carcinogenic than either 1-nitrosopyrene or 1-aminopyrene.