Induction of Flavin-Containing Monooxygenase (FMO B) in Rabbit Lung and Kidney by Sex Steroids and Glucocorticoids

Modulation of lung and kidney levels of flavin-containing monooxygenase (FMO) isoform B following sc administration of dexamethasone, progesterone, β-estradiol, aldosterone, or β-estradiol plus progesterone was examined in male rabbits. Both dexamethasone and progesterone increased FMO B protein levels in lung. N-Oxygenation of N,N′-dimethylaniline (DMA) was significantly induced in lung microsomes from rabbits treated with progesterone. In kidney, only dexamethasone was effective in inducing FMO B protein levels and DMA N-oxygenation. Surgical implantation of osmotic pumps containing β-estradiol or progesterone into non-pregnant female rabbits resulted in elevated plasma levels of these steroids after 4-5 days at which point the lung levels of FMO B were induced by 35 and 82% for β-estradiol and progesterone, respectively. The responsiveness of FMO B in lung to both progesterone and glucocorticoids and in kidney to only the latter is consistent with the developmental pattern of both maternal FMO B and peak plasma levels of these steroids during pregnancy.