Enlarged nuclei have been observed frequently as an early carcinogen-induced change in both cultured cells and in target tissues in vivo. The purpose of this work was to examine the occurrence of nuclear enlargement in the upper respiratory tract of rats to provide further evidence of whether nuclear enlargement is a reliable marker of carcinogenesis, and if it could be used as a short-term test for respiratory carcinogens.
Carcinogen-induced nuclear enlargement is best demonstrated in vivo when the tissue involved has been undergoing rapid replication. Male Wistar albino rats were simultaneously exposed to an atmosphere containing sulphur dioxide (which caused a hyperplastic response in the nasal cavity) and received an i.p. injection of a nitrosamine. Sections were prepared from the nasal cavity, and the nuclear areas of respiratory epithelial cells were measured. There were some increases in nuclear size 24 and 72 h after the start of treatment. The reversal of this effect 120 h after the start of treatment may have been due to the loss of the normal ciliated mucosal epithelium, and subsequent loss of metabolic capability.