Histologic study of tissues and organs from rats exposed to vapors of 2-nitropropane at 25 ppm

Male and female Sprague-Dawley rats were exposed by inhalation to 2-nitropropane at a concentration of 25 ppm for 7 hr per day, 5 days per week over a period of 22 months. Groups of animals were killed periodically during the study for interim evaluations and all animals remaining alive were killed after 22 months of exposure. Histologic preparations were made from all major organs and tissues from each animal and examined microscopically. No incidence of benign or malignant tumors, nor any lesion, nor the onset of any disease was observed which could be attributed to the exposure to 2-nitropropane. The pattern of tumor formation which was observed was similar to that usually observed in the aging rat, in particular, the multiple endocrine tumor syndrome. The distribution of tumors and other lesions was similar in control and exposed groups of rats.