Nicotinamide-induced hepatic microsomal mixed function oxidase system in rats.

Area of Science:

• Biochemistry
• Pharmacology
• Toxicology

Background:

• The hepatic microsomal mixed function oxidase system is crucial for drug metabolism.
• Understanding inducers of this system is vital for drug development and toxicology.
• Nicotinamide is an endogenous metabolite with potential biological activities.

Purpose of the Study:

• To investigate the effect of nicotinamide on the hepatic microsomal mixed function oxidase system in male rats.
• To compare the induction pattern of nicotinamide with other compounds like phenobarbital.

Main Methods:

• Administration of nicotinamide, tryptophan, nicotinic acid, and methionine to male rats via intraperitoneal injection.
• Measurement of hepatic NADPH-cytochrome c reductase, cytochrome P-450, and cytochrome b5 levels.
• Assay of drug-metabolizing enzyme activities, including arylhydrocarbon hydroxylase, aminopyrine demethylase, and UDP-glucuronosyltransferase.
• Assessment of protein synthesis using 14C-labelled leucine incorporation and inhibition studies with puromycin.

Main Results:

• A single dose of nicotinamide (100 mg/kg) significantly induced all measured components of the hepatic microsomal mixed function oxidase system.
• Tryptophan, nicotinic acid, and methionine also showed induction of hepatic NADPH-cytochrome c reductase activity.
• Nicotinamide-induced enzyme activity was linked to increased protein synthesis, inhibited by puromycin.
• Nicotinamide demonstrated a unique induction pattern distinct from phenobarbital.

Conclusions:

• Nicotinamide is a potent inducer of the hepatic microsomal mixed function oxidase system in rats.
• The induction mechanism involves increased hepatic microsomal protein synthesis.
• Nicotinamide's effect differs from that of phenobarbital, suggesting a unique pathway of induction.