In perfused livers from fed and fasted B-naphthoflavonetreated C57BL/6J mice

maximal rates of p-nitroanisole O-dernethylation were 30-40 u moles/g/br and 15-20 u moles/g/hr respectively. The detergent saponin

at concentrations ranging from 0.001 to 0.005%

was infused between 2 and 30 min to establish optimal conditions to pertneabilize plasma membranes. Perm-eabilization was assessed by release of lactate dehydrogesase and stimulation of p-nitroanisole O-deinqthylation or conjugation of p-nitrophenol by perfused livers. Further

dicarboxylates or NADPH bad no effect on rates of monooxygenation by perfused mouse liver in the absence of saponin. In saponin-treated livers from fasted mice

however

rates of monooxygenation were increased rapidly by Infusion of dicarboxylates (10 mM malate

citrate

or isocitrate) or an NADPH-generating system (60 and 110% respectively)

over a 6-8 min period. During this time period

cellular energetics were not comprised as reflated by normal rates of glucuronidation of p-nitrophenol. Thus

non-permeable .metabolites can enter saponin-permeabilized cells in the perfused liver. Rates of monooxygenation were increased 40-60% in livers from fed mice by citrate

NADPH(200uM) or an NADPH-generating system. By contrast. sapoaic decreased mixed-function oxidation assayed in isolated microsomes incubated with an NADPH-generatingsystem. Taken together

these data support the hypothesis that maximal rates of monooxygenation in intact hepatocytes from fed as well as fasted mice is limited by the availability of NADPH