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The mechanism of induction of an adult rabbit cytochrome P-450, prostaglandin (PG) omega-hydroxylase (P-450PG-omega), during pregnancy has been investigated. This P-450 isozyme regiospecifically hydroxylates PGE1, PGA1, and PGF2 alpha at carbon-20 (the omega position). The specific activity of this enzyme is induced from 0.07 nmol of 20-OH-PGE1 to 3.05 nmol of 20-OH-PGE1 formed per min per mg of microsomal protein in the lungs of 25- to 28-day pregnant rabbits as compared to nonpregnant rabbits. Immunoblotting studies with a polyclonal antibody raised against this P-450 have shown that there is a concomitant gestational age-dependent increase in the amount of P-450PG-omega microsomal protein accompanying the increase of omega-hydroxylase activities. Within 3 days postpartum, both omega-hydroxylase activity and the amount of immunodetectable P-450PG-omega drop precipitously to near control levels. In vitro translation of total cellular RNA, extracted from the lungs of pregnant rabbits at various days throughout gestation, and immunoprecipitation of newly synthesized P-450PG-omega demonstrated a similar gestational age-dependent increase in translatable P-450PG-omega mRNA, as was observed with omega-hydroxylase activity and P-450PG-omega protein levels. These data suggest that the induction of this P-450 may occur at the transcriptional level and, furthermore, that control of cytochrome P-450PG-omega expression in the rabbit lung is tightly regulated at both protein and mRNA levels.