Table 2

Fold increase in testosterone 6β-hydroxylase activity, immunoreactive protein, and mRNA levels in hepatocytes treated with tamoxifen, 4-hydroxytamoxifen, rifampicin, and phenobarbital, relative to untreated control

	Rifampicin^2-a 10 μM	Phenobarbital^2-a 2 mM	Tamoxifen		4-Hydroxytamoxifen
	Rifampicin^2-a 10 μM	Phenobarbital^2-a 2 mM	1 μM	5 μM	10 μM	1 μM	5 μM	10 μM
CYP3A4 activity^2-b n = 4	10.54 ± 1.89	8.95 ± 2.97	1.30 ± 0.15	2.12 ± 0.77	2.4 ± 0.39	2.05 ± 0.38	7.51 ± 2.61	6.38 ± 1.14
CYP3A4 protein levels n = 4	9.43 ± 3.83	7.65 ± 2.8	1.51 ± 0.11	4.03 ± 1.92	4.46 ± 1.64	1.6 ± 0.17	5.79 ± 1.05	7.41 ± 1.69
CYP3A4 mRNa levels n = 2	13.46 ± 6.77	12.01 ± 5.3		3.3 ± 0.37	4.8 ± 1.63		5.57 ± 1.03	9.03 ± 3.1

Various batches of hepatocytes (n = 4) were treated with these agents at the indicated concentration for a period of 72 h. Cells were then exposed to testosterone-containing medium (250 μM) for 30 min. The 6β-hydroxytestosterone levels in the supernatant medium were determined employing HPLC/UV analysis. The immunoreactive CYP3A4 levels in protein fractions prepared from harvested hepatocytes were determined by Western blot analysis employing a monoclonal anti-CYP3A4 antibody. The CYP3A4 mRNA levels were determined by Northern blot analysis of total RNA employing a radiolabeled 780-base pair cDNA probe and normalized to the 18S rRNA levels in respective groups.

↵2-a Rifampicin and phenobarbital were employed as positive controls for CYP3A4 induction.
↵2-b CYP3A4 activity was determined by measuring the testosterone 6β-hydroxylation, mean ± S.E.M. from four batches of hepatocytes.