Foetal and placental ornithine decarboxylase activity in the rat--effect of maternal undernutrition.

The activity of the enzyme ornithine decarboxylase and the accumulation of nucleic acids were examined in the rat foetus and placenta during normal development and during maternal undernutrition. Maternal undernutrition resulted in a reduced rate of increase in weight of both the foetus and placenta towards the end of gestation. In the placenta the failure to increase in weight was accompanied by a failure of DNA to increase. In the foetus the amount of DNA failed to increase over a short period and then made a compensatory response to return to a normal amount by the end of gestation. Undernutrition failed to affect RNA in either the foetus or placenta. These results differ from those obtained during maternal protein deficiency. The activity of foetal and placental ornithine decarboxylase was normal during much of gestation in the undernourished group. However, at the same time as the compensatory increase in foetal DNA, there was a marked increase in enzyme activity in both tissues. It is suggested that a single compensatory stimulus is responsible for the changes in both ornithine decarboxylase and DNA.