Corticosteroids, Ornithine Decarboxylase Activity and the Incorporation of Leucine, Uridine, and Thymidine into Mouse Placenta

Abstract

Summary: The in vitro incorporation into mouse placenta of [¹⁴C]leucine, [³H]uridine, and [ ³H)thymidine fell between gestational days 14 and 19 by 61, 30, and 72% respectively; ornithine decarboxylase activity fell by 75% Injection of dexamethasone resulted on day 14 in values normally found between days 15 and 18. These changes coincided with rising activity in fetal liver of the enzyme 11β-hydroxysteroid:NADP oxidoreductase, which reduced the abundant 11-dehydrocorticosterone to the active hormone, corti-costerone. These events appear to be part of a spectrum of effects produced by corticosteroids on fetal growth at this time, probably mediated primarily by fetal liver. Speculation: The events induced by corticosteroids in placenta and brain involve changes in the enzyme which interconverts corticosterone and its inactive 11-dehydrometabolite. The same relationship has been reported between this enzyme and maturation of rat and rabbit lung, but at a later state of gestation. This suggests that regulation of these phenomena is not simply due to a rise in circulating hormone level, but involves enzyme activities in tissues which function to some extent independently,