Corticosterone Metabolism and the Incorporation of Leucine, Uridine, and Thymidine into Fetal Mouse Brain

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

“…however, does not appear to have been reported previously. The decrease in the incorporation of leucine, uridine and thymidine observed here (Table 1) is similar to that observed in fetal brain (7). also attributed to an increase in active corticosteroid.…”

“…Inhibition of this reaction prevented maturation of fetal rat lunq, as measured by phospholipid synthesis (5). Rising reductase activity in fetal mouse liver (3) coincided with a decrease in the dehydrogenation reaction in mouse brain, which was considered responsible for a marked decrease in the rate of incorporation of leucine, uridine and thymidine into fetal mouse brain (7). This communication describes similar effects in mouse placenta, indicating an action of corticosteroids on this tissue.…”

“…The decrease in ornithine decarboxylase activity parallelled that of thymidine incorporation in both placenta (Table 1) and in fetal brain (7). Ornithine decarboxylase is an indicator of change in metabolic or proliferative activity of tissues induced by hormones (6).…”

“…Subsequently, however, using double isotope labelling of substrates to ascertain both dehydrogenase and reductase activities simultaneously, it was found that the ratio of reduction/dehydrogenation in placenta remains around 4 ( Fig. l), while the brain is the major site of dehydrogenation (3,7). Conceivably the placenta functions to reduce the metabolite formed in fetal tissues before returning it to the maternal compartment.…”

“…The timing of pregnancies, the preparation and incubation of tissues and measurement of incorporation of le~cine-'~c(u), uridine-53~ and thymidine methyl-'H into the acid-insoluble components of tissues have been described earlier (7). The preparation of ll-dehydrocorticosterone-4-"C and incubation of it and corticosterone-4-''c with tissues and the preparation of autoradiograms has also been described therein.…”