Histopathologic Examinat10Ns of Rats Treated by Inhalations of Various Types of Nickel Compounds

Abstract

Histopathological changes in rats, including tumorigenesis in the respiratory system, caused by inhalations of three types of nickel compound aerosol were examined. Using a special exposure system developed by us, male Wistar rats were made to inhale green nickel oxide [NiO(G)], black nickel oxide [NiO(B)], and nickel subsulfide (Ni₃S₂). Ten rats of each group were sacrificed immediately after an inhalation period of 6 mo, and 47 NiO(G)-inhaled, 40 NiO(B)-inhaled, and 47 Ni₃S₂-inhaled rats were sacrificed after a postinhalation clearance period of 12 mo. Each group was accompanied by 20 control rats. No tumors were found in any of the experimental rats immediately after the inhalations. Foam-cell aggregations and alveolar exudates in the lung and bronchopneumonia were more remarkable in the Ni₃S₂ group than in both NiO(G) and NiO(B) groups. As for the groups after the clearance period, a small number of lung tumors, for example, one adenocarcinoma in the NiO(G) group, four adenomas in the NiO(B) group, and one adenoma in Ni₃S₂ group, occurred. Sporadic tumors of other organs were also noted. Three pulmonary adenomas were also found in all 60 control rats, and there was no significant difference in the occurrence of lung tumors between the nickel-inhaled and noninhaled control groups. It was concluded that the inhaled NiO(G), NiO(B), and Ni₃S₂ in our study did not show apparent accelerating effects on tumorigenesis in any organ.