CORRELATION BETWEEN IN VIVO AND IN VITRO ACTIVITIES OF ALDEHYDE OXIDASE

Correlation between in vivo and in vitro activities of aldehyde oxidase was examined in several mammalian species. The in vitro activity was determined by measuring oxidation of N1-methylnicotinamide to the corresponding 2-pyridone and 4-pyridone derivatives by liver cytosols. On the other hand, the in vivo activity of the enzyme was determined by measuring above pyridone derivatives as urinary metabolites of nicotinamide. Marked strain differences were observed when aldehyde oxidase activity of liver cytosols was examined in five strains of rats (Sea:SD, Jcl:SD, Std:Wistar/ST, Crj:CD and WKA/Sea). The in vitro activity was well correlated with the in vivo activity of the enzyme in these strains. Significant species differences were observed when aldehyde oxidase activity was examined in rabbits, guinea pigs, hamsters, monkeys and dogs. The in vitro activity was also correlated with the in vivo activity of the enzyme in these species. Human liver cytosols exhibited relatively high aldehyde oxidase activity which was variable individually. Such variabilityof aldehyde oxidase activity in human was also observed in the in vivo studies.