[Mechanism of riboflavin deficiency facilitating carcinogenesis of N-nitrosamine--effect on carcinogen-metabolizing enzymes].

Previous studies have demonstrated the facilitating effect of riboflavin deficiency on the carcinogenesis of the liver of rats induced by N-nitrosamine. However, the mechanism was still not clear. In the present investigation, the alterations of microsomal carcinogen-metabolizing enzymes of rat liver during riboflavin-deficiency with simultaneous administration of nitrosodimethylamine (NDMA) were studied. The results showed that the enzyme activities of hepatic microsomal cytochrome P-450 and NDMA demethylase of riboflavin deficient rats and riboflavin deficient rats receiving NDMA were increased and significantly different from the control rats (P less than 0.05). The enzyme activities of hepatic microsomal NADPH-cytochrome P-450 reductase of riboflavin deficient rats and riboflavin deficient rats receiving NDMA were significantly decreased (P less than 0.01). All the alterations disappeared after supplying riboflavin to the deficient rats. This result indicates that the effect of riboflavin deficiency on carcinogen-metabolizing enzymes of rat liver is reversible.