Effect of ascorbic acid and some reducing agents on N-nitrosopiperidine metabolism by liver microsomes

The effect of ascorbic acid on the oxidation of N-nitrosopiperidine by a microsomal preparation obtained from guinea-pig liver has been examined. The metabolites from the oxidation of N-nitrosopiperidine were found to be 5-hydroxypentanal (about 1.93%), N-nitroso-3-hydroxypiperidine (about 0.02%), and N-nitroso-4-hydroxypiperidine (about 0.15%). With microsomes separated from the liver of guinea-pigs pretreated with phenobarbital and 3-methylcholranthrene, the yields of N-nitroso-3-hydroxypiperidine and N-nitroso-4-hydroxypiperidine were found to decrease upon increasing the concentration of ascorbic acid in the reaction mixture. In the presence of small amounts of ascorbic acid, the yields of these compounds with untreated liver microsomes apparently increased, while the presence of larger amounts of ascorbic acid caused a decrease in the yields of these metabolites. In contrast with the yields of N-nitroso-3-hydroxypiperidine and N-nitroso-4-hydroxypiperidine, that of 5-hydroxypentanal decreased with increasing amounts of ascorbic acid.