Table 5

NADPH-supported rates of NADPH and substrate oxidations and H₂O₂ formation in liver microsomes from rats untreated and orally treated with phenytoin

Substrate	Product	Untreated	Phenytoin-Treated	Fold Increase in Coupling Ratio
		nmol/min/nmol P450
None	Oxidized NADPH	13 ± 3 (100)	9 ± 3^5-150 (100)
	H₂O₂	2.0 ± 0.7 (15)	4.2 ± 0.9^5-160 (22)
Testosterone	Oxidized NADPH	15 ± 2 (100)	19 ± 3 (100)
	Oxidized testosterone^5-a	2.6 ± 0.4 (17)	5.5 ± 0.9^5-160 (29)	1.7
	H₂O₂	2.3 ± 0.5 (15)	3.1 ± 0.4 (16)
Phenytoin	Oxidized NADPH	11 ± 2 (100)	17 ± 3^5-150 (100)
	Oxidized phenytoin^5-b	0.15 ± 0.01 (1.4)	0.04 ± 0.01^5-160 (0.2)	0.14
	H₂O₂	1.3 ± 0.4 (12)	3.4 ± 0.7^5-160 (20)
4′-HPPH	Oxidized NADPH	12 ± 3 (100)	18 ± 3^5-150 (100)
	3′,4′-diHPPH	0.48 ± 0.09 (4)	0.24 ± 0.03^5-160 (1)	0.25
	H₂O₂	1.5 ± 0.4 (13)	2.3 ± 0.7 (13)

Data are mean ± S.D. for four rats. The number in parentheses indicate percentage of product formation to oxidized NADPH (coupling ratio).

Significantly different from untreated group (
↵5-150 p < 0.05;
↵5-160 p < 0.01).
↵5-a Sum of rates of 6β-, 16α-, 16β-, 2α-, and 2β-hydroxylated testosterone formation at 100 μM testosterone.
↵5-b Sum of rates of 4′-HPPH, 3′-HPPH, and 3′,4′-diHPPH formation at 100 μM phenytoin.