Experimental oral cancer in rats with xerostomia

Though previous experiments with fat-soluble carcinogens have demonstrated a protective effect of the saliva against chemically induced oral cancer it is not known if this also holds true for water-soluble carcinogenic agents. In vitro experiments indicate that the water-soluble 4NQO (4-nitrochinoline N-oxide) easily penetrates a layer of saliva similar with that normally present on the oral mucous membranes. It is possible that this quality, on intraoral applications of 4NQO, could eliminate the protective barrier of saliva. The protective effect of the saliva was examined in the present investigation. Xerostomia was induced in 15 rats and 4NQO was applied to the palate 3 times a week. After 4.7 months, on an average, palatal cancer appeared in all rats. In comparable investigations the result was 7 months with rats treated in an identical manner except for their salivary secretion remaining intact. This time difference represents approximately 33% of the time necessary for the development of oral cancer in normal rats by means of 4NQO. It was concluded, that a protective effect of the saliva exists whether the oral mucous membranes are attacked by water--or fat-soluble carcinogens.