Prochloraz, a potent inducer of the microsomal cytochrome P-450 system

Prochloraz ( N-propyl- N-[2-(2,4,6-trichlorophenoxy)ethyl]-imidazole-1-carboxamide), a recently developed agricultural fungicide, is a potent inducer of microsomal enzymes. Rats fed 7 days with a prochloraz-contaminated diet (2500 ppm) showed an increase in hepatic cytochrome P-450, cytochrome b 5, and microsomal protein level; aniline hydroxylase, 7-ethoxycoumarin dealkylase, 7-ethoxyresorufin dealkylase, NADPH-cytochrome c reductase, and epoxide hydrolase were significantly induced. At a lower dose (100 ppm), only an increase in cytochrome P-450 and 7-ethoxyresorufin dealkylase was noticed. As shown with aniline hydroxylase and 7-ethoxycoumarin dealkylase, prochloraz is also a potent inhibitor of drug-metabolizing enzymes. The interaction of prochloraz with hepatic microsomal fraction from rat liver was also studied. Prochloraz binds to oxidized cytochrome P-450 to produce a type II spectral change; the compound also binds to reduced cytochrome P-450. The binding of some ligands (7-ethoxycoumarin, n-octylamine, aniline, and imidazole) to oxidized cytochrome P-450 was determined after induction by prochloraz. Japanese quails ( Coturnix coturnix) fed 7 days with a prochloraz-contaminated diet (2000 ppm) showed a dramatic increase in liver weight (2.5-fold) and both hepatic and duodenal cytochrome P-450 (9- and 12-fold, respectively).