The effect of ultra-violet radiation and restricted diet on rat labial mucosa

The combined effect of ultra-violet radiation and a restricted diet on oral mucosa was investigated using the labial mucosa of pigmented rats. Twenty-four rats were divided so that 12 experimental animals received 50% of the average daily diet of the remaining 12 normal controls. After 1 month, the epithelium of the restricted group had thinned to 2/3 of that of the controls. Nine rats from each group were then subjected to daily ultra-violet irradiation of the labial mucosa, three animals in each group remaining as unirradiated controls. After 1, 4 and 8 weeks irradiation, three experimental and one unirradiated control from each group were sacrificed. Microscopic examination showed that the thickness of the epithelium and the mitotic index increased in both normal and restricted animals at 4 weeks. The increase in thickness was maintained at 8 weeks, but the mitotic index declined in the deficient animals at this time. Evidence of epithelial dysplasia was seen in the normal animals at 4 weeks, and this increased at 8 weeks; such changes were rarely seen in the restricted animals. It thus appears that the extent of ultra-violet induced dysplasia may be related to the mitotic index, a lower mitotic index implying less dysplasia.