Genetic regulation of NADPH supply in perfused mouse liver. Role of the Ah locus during induction by 3-methylcholanthrene.

Rates of p-nitroanisole O-demethylation in perfused livers from control DBA/2J and C57BL/6J, as well as from 3-methylcholanthrene-treated DBA/2J mice, reached maximal values of 15-17 mumol/g/h after 10 min of p-nitroanisole (0.2 mM) infusion. During the subsequent 30 min of p-nitroanisole infusion these rates declined steadily to 50% of the maximal rate. Infusion of 20 mM glucose completely reversed this decline in rate. Phenobarbital treatment of C57BL/6J and DBA/2J mice increased rates of p-nitroanisole O-demethylation about 2.5-fold to 44.4 +/- 3.4 and 35.1 +/- 3.4 mumol/g/h, respectively, which also declined during subsequent perfusion. In contrast, the kinetics of p-nitroanisole O-demethylation in perfused livers from 3-methylcholanthrene- and beta-naphthoflavone-treated C57BL/6J were distinctly different. These livers maintained high maximal rates of p-nitroanisole O-demethylation (41.1 +/- 4.7 mumol/g/h) throughout the 40 min of p-nitroanisole infusion. 3-Methylcholanthrene-treated (C57BL/6J)(DBA/2J)F1 perfused livers also maintained high rates of monooxygenation throughout the perfusion. All livers from the 3-methylcholanthrene-treated, Ah locus-responsive F1 X DBA/2J backcross group maintained high rates of p-nitroanisole O-demethylation throughout perfusion; however, 3-methylcholanthrene-treated, Ah locus-nonresponsive perfused livers resembled livers from untreated mice. The NADP+/NADPH ratio in livers from 3-methylcholanthrene-treated C57BL/6J but not DBA/2J mice was significantly higher than controls in the absence of p-nitroanisole. Addition of p-nitroanisole increased this ratio in both groups; however, higher values were observed in livers from C57BL/6J than DBA/2J mice. These data provide genetic evidence that the ability of mouse liver to sustain high rates of monooxygenation following 3-methylcholanthrene treatment is an autosomal dominant trait corresponding with the Ah locus and most likely is due to enhanced NADPH turnover.