Table 1

Comparison of in vivo and in vitro induction of rat liver CYP enzymes by prototypical inducers

P-450 Enzyme^1-a	In Vivo Induction in Male Rats^1-b		In Vitro Induction in Hepatocytes^1-c
P-450 Enzyme^1-a	Control Activity^1-d	Induced Activity	Control Activity	Induced Activity
CYP1A	152 ± 27	3,320 ± 183	24.0 ± 15.3	513 ± 12.0
CYP2B	23.8 ± 4.2	1,460 ± 180	2.25 ± 2.1	615 ± 101
CYP3A	2,460 ± 780	12,693 ± 2,255	208 ± 60	2,670 ± 410
CYP4A	489 ± 52	10,693 ± 620	430 ± 80	2,700 ± 600

↵1-a The enzyme activities of CYP1A, CYP2B, CYP3A, and CYP4A enzymes were determined as 7-ethoxyresorufinO-dealkylation, 7-pentoxyresorufinO-dealkylation, testosterone 6β-hydroxylation, and lauric acid 12-hydroxylation, respectively (Pearce et al., 1996).
↵1-b Liver microsomes from male Sprague-Dawley rats treated with P-450 enzyme inducers. Rats were dosed once per day for 4 days with isotonic saline, β-naphthoflavone, phenobarbital, dexamethasone, or clofibric acid at a dosage of 5, 100, 80, 50, and 200 mg/kg, respectively. Data on the activity of P-450 enzymes were provided by XenoTech, LLC (Kansas City, KS).
↵1-c Liver microsomes from cultured rat hepatocytes were treated with P-450 enzyme inducers and activity of P-450 enzymes was determined as described in Experimental Procedures. Data are the means ± S.E. from three separate experiments (Fig. 8).
↵1-d Activities are reported as pmol/min/mg protein and are averages of duplicate determinations from three to five experiments.