Relationship between the ability of nicotinamide to maintain nicotinamide-adenine dinucleotide in rat liver cell culture and its effect on cytochrome P-450.

Rat hepatocytes cultured for 24 h lose 60% of their NAD content. Treatment with nicotinamide prevents the loss of NAD as well as the previously reported loss of cytochrome P-450, suggesting a possible causal relationship. However, isonicotinamide also prevents the loss of cytochrome P-450, but does not increase the concentration of NAD, demonstrating that the ability of nicotinamide to maintain cytochrome P-450 is not apparently related to its effect on the NAD content of cultured hepatocytes.