Metabolism of 2-acetylaminofluorene in isolated rabbit pulmonary cells. Evidence for the heterogeneous distribution of monooxygenase activity in lung tissue.

The regiospecific hydroxylation of 2-acetylaminofluorene (2-AAF) has been used to monitor monooxygenase activity in isolated rabbit lung cells. Following isolation, the cells were separated into seven different fractions according to size by centrifugal elutriation. Macrophages were recovered from the lungs by lavage and examined in parallel with the parenchymal cell populations. The resulting fractions were assayed for 2-AAF hydroxylase activity and were examined for the presence of endothelial cells (angiotensin-converting enzyme), alveolar type II cells (modified Papanicolaou stain), polymorphonuclear leukocytes (modified Papanicolaou stain), bronchiolar Clara cells (nitro blue tetrazolium stain), and ciliated cells (phase contrast microscopy). Highest hydroxylase activities were seen in the cell fraction containing the largest percentage of Clara cells. The activity profiles provided evidence for a population of cells not correlating with either alveolar type II cells or Clara cells possessing substantial monooxygenase activity. The alveolar macrophage almost exclusively hydroxylated 2-AAF in the 9-position and the cell fraction containing the higher percentage of endothelial cells metabolized 2-AAF the least. Pretreatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin preferentially induced the 7-hydroxylation of 2-AAF and either did not alter or decreased the rate of formation of the other hydroxy metabolites. An exception was seen in fraction 1 where 2,3,7,8-tetrachlorodibenzo-p-dioxin induced the hydroxylation of 2-AAF to all products except 3-hydroxy-AAF. Evidence is presented for the presence of a cell type(s) not identifiable as either the Clara or alveolar type II cell with considerable monooxygenase activity.