The combined effects of asbestos ingestion and localized X-irradiation of the colon in rats.

We hypothesized that the normal bowel may afford some protection to tissue penetration of ingested asbestos, due to the mucus produced by goblet cells which normally coats the gut surface. To study this, we exposed localized segments of the colons of laboratory rats to X-irradiation. These animals were then divided into 3 groups which were fed either a diet containing 10% chrysotile asbestos, a diet containing 10% non-nutritive cellulose fiber, or a standard laboratory diet. Autopsies and histopathology were performed on all animals that died spontaneously and those that were killed at 350 days. Various types of inflammatory and degenerative lesions were commonly seen, but there was little difference in frequency between the diet groups. Five adenocarcinomas and two sarcomas were seen in the fiber groups (three tumors in the asbestos group and four tumors in the cellulose group) but no tumors were seen in animals on the standard diet. There was not a significant difference in tumor rates between the asbestos and cellulose groups, nor was there a significant difference between the combined fiber groups and the standard diet group. It was concluded that the x-ray treatment resulted in localized damage to the colonic mucosa and, therefore, theoretically disrupted the normal mucus coating allowing the potential for increased tissue penetration by the asbestos. Ingested asbestos did not increase the risk for tumor development and, therefore, does not seem to be co-carcinogenic or a tumor promoter in combination with disruption of mucus coating and localized X-irradiation.