Cytochrome P450-linked p-nitroanisole O-demethylation in the perfused lung.

Oxidative demethylation of p-nitroanisole, a cytochrome P450-linked mixed-function oxidation, was evaluated in isolated perfused rat and rabbit lungs. The product, p-nitrophenol, was monitored continuously in the lung effluent by spectrophotometric measurement. Pulmonary p-nitrophenol production in mumol/h per g dry wt was 6.2+/-0.4 by rabbits and 2.0+/-0.3 by rats (mean+/-SE). Maximal activity of the reaction required pulmonary perfusion rates in excess of 60-80 ml/min per g of dry lung. The half-maximal rate of p-nitrophenol production was observed with p-nitroanisole concentration of 13 micron. Pretreatment of rabbits with chlorpromazine increased p-nitroanisole O-demethylation activity by 63% but phenobarbital pretreatment had no effect. Ventilation with 75% carbon monoxide plus 20% O2 reversibly inhibited the reaction. Specific activity of p-nitroanisole demethylase in the microsomal fraction was 0.5 nmol/min per mg protein in rabbit lungs and 0.1 nmol/min per mg protein in rat lungs. Other rabbit lung subcellular fractions compared with microsomes had significantly lower specific activity. This study demonstrates that p-nitroanisole O-demethylation can be continuously monitored in the intact lung and describes conditions necessary for maximal activity of this pathway.