The use of new methods to measure: The effect of diet and inducers of microsomal enzyme synthesis on cytochrome P-450 in liver homogenates, and on metabolism of dimethyl nitrosamine

Abstract

Modified methods for measurement of cytochrome P-450 content of liver homogenates, and of formaldehyde produced in demethylation reactions are described. These methods have been used to measure cytochrome P-450 content, and metabolism of dimethyl nitrosamine in rat liver. Over 80 per cent of cytochrome P-450 present in liver homogenate of phenobarbitone treated rats could be recovered in the microsomal fraction. Feeding a low protein-low fat diet reduced the P-450 content of homogenate. and also reduced the recovery of cytochrome P-450 in the microsomal fraction to 50 per cent or less. The rate of metabolism of dimethyl nitrosamine in vivo and in vitro was increased by fasting and by phenobarbital treatment, and decreased by feeding low protein diet. Benzo(α)pyrene treatment caused a slight increase in the rate of DMN metabolism in vivo and in microsomes. The toxicity of dimethyl nitrosamine is not altered in parallel with changes in the rate of metabolism. It is suggested that the amount of toxic metabolite is more important than the rate at which it is formed.