Activity of placental enzymes of carbohydrate and lipid metabolism in normal, toxemic and small-for-date pregnancies.

The specific activity of placental enzymes with a regulatory function in the pathways of glycolysis, gluconeogenesis, NADPH generation and fatty acid synthesis decrease during gestation in the rat. Similar decreases occur in the activity of enzymes of the human placenta when compared between early gestation and term, with the exception of the activity of enzymes related to gluconeogenesis which tend to increase as gestation advances. In term placentas from pregnancies complicated by preeclamptic toxemia, enzyme activities were significantly lower than those in placentas from normal pregnancies, irrespective of whether the baby was of normal weight or small-for-date. This indicates an accelerated decline in placental metabolic function in toxemia. In contrast, in placentas from nontoxemic pregnancies with small-for-date babies the enzyme activities were significantly higher than those in normal term placentas. It is suggested that the decrease in placental enzyme activity, which is associated with placental growth during the course of normal gestation, is retarded in nontoxemic pregnancies with small-for-date babies, apparently due to the arrested aging of the placenta.