[Metabolic significance of cyclic nucleotides in the environment for fetal growth--effects of PGI2-like substance on fetal platelet function].

Prostacyclin (PGI2), the major active metabolite of arachidonic acid in the vascular endothelium, is characterized by antiaggregatory and vasodilator properties. In this report, the significance of PGI2 and TxA2 on fetal platelets was studied. Platelet aggregation induced by ADP, collagen and adrenalin were found to be augmented in maternal blood but suppressed in umbilical cord blood. A much larger amount of PGI2-like substance was released from the umbilical cord artery and vein than from the intraplacental vein and chorionic tissue. On the other hand, the generation of this substance was reduced in the umbilical cord artery (4.4 +/- 2.7 nmoles/mg tissue/hour) and vein (2.9 +/- 2.1 nmoles/mg/tissue/hour) in patients with severe pre-eclampsia associated with IUGR. The plasma beta-thromboglobulin level is higher in maternal and umbilical cord blood, than in control group. Plasma 6-Keto-PGF1 alpha, TxB2, cyclic AMP and cyclic GMP values were significantly (p less than 0.05) higher in umbilical cord blood than in maternal blood, but serum phosphodiesterase activity showed no difference between mother and fetus. These results indicate that various factors, such as PGI2, TxA2 and cyclic nucleotides, may co-exist in high levels in the fetus, and the balance is needed for the maintenance of physical interaction between the platelet and vascular wall in the fetal blood vessels. PGI2 in particular may play an important role in this balance and in the regulation of placental-fetal circulation.