Chronic inhalation of asbestos and cigarette smoke by hamsters.

One hundred and two male Syrian golden hamsters received chronic exposures to a respirable aerosol of Canadian chrysotile asbestos (mean aerosol concentration = 23 μg/l) 7 hours per day, 5 days per week. Half of the animals were also exposed for 10 minutes to cigarette smoke in modified Hamburg II smoking machines, three times per day, 5 days per week, for the duration of their life span. The other half of the animals received sham-smoke exposures. Another group of 102 hamsters served as controls. Half of the controls received smoke exposures, the other half received sham exposures. Asbestos exposure resulted in earlier and more severe lung lesions than in identical groups of concurrent experiments, which had received life span exposures to aerosols of NiO (53 μg/l) and CoO (10 μg/l), or which were treated with diethylnitrosamine (12 × 0.25 mg by s.c. injection). Asbestosis developed in all animals and forced discontinuation of the asbestos exposures after 11 months. Of 12 lung adenomas found in 510 hamsters, ten occurred among the 102 animals of the asbestosexposed groups, indicating an early neoplastic response. However, perhaps on account of their significantly shorter life span due to asbestosis, the incidence of laryngeal lesions and of malignant tumors wassignificantly lower in the asbestos + smoke-exposed group than in the control group having received smoke exposures. Neither a carcinogenic effect of asbestos nor a cocarcinogenic effect of cigarette smoke was observed. Cigarette smoke inhalation resulted in significantly lower mean body weights of the smoke-exposed groups.