The aims of the present study were to determine cytochrome P450 enzyme activity 
in six strains of experimental rodents (n = 5/sex/species): ICR, C57BL/6 and 
DBA/2 mice; Sprague Dawley and Wistar rats; and Dunkin Hartley guinea pigs. 
After animals were treated with the typical inducers β-naphthoflavone (BNF), 
dexamethasone (DEX) and phenobarbital (PB), the levels of O-dealkylation of 
ethoxyresorufin (EROD), methoxyresorufin (MROD), pentoxyresorufin (PROD) and 
benzyloxyresorufin (BROD) activity were determined using responsive catalytic 
reactions to study CYP1A1, CYP1A2 and CYP2B, respectively. A maximal induction 
of EROD and MROD was found in BNF-treated animals from all strains (2.4- to 
15.1-fold) except DBA/2 (0.9- to 1.8-fold). C57BL/6 mice had the strongest 
BNF-induced EROD (15.1-fold) and MROD (8.3-fold) activities. No differences in 
BNF-induced EROD and MROD activities were observed between males and females. 
However, the EROD activity of Wistar rats and the MROD activity of Sprague 
Dawley rats were higher in males than females. DEX induced PROD activity only in 
mice (1.3- to 7.1-fold), but not in rats and guinea pigs (0.2- to 1.1-fold). 
However, induction of BROD activity was found in DEX-treated mice and rats (1.5 
to 12.5-fold), but not in guinea pigs (0.3 to 0.4-fold). PB caused a significant 
elevation of PROD (1.7- to 10.4-fold) and BROD (31- to 13.2-fold) activities in 
all the animals. PB-induced BROD activity was higher in females than males in 
Sprague Dawley rats. These observations strongly suggest that the choice of 
experimental animal strain, species and inducer is of critical importance for 
studies of drug metabolism and interaction.