[Ultracytochemical localization of cyclic 3',5'-nucleotide phosphodiesterase activity in human term placenta]

Reports have so far accumulated suggesting that cyclic nucleotide may play an important role in the regulation of placental function. Cyclic 3',5'-nucleotide phosphodiesterase (PDE) is the enzyme which degrades cyclic nucleotide to nucleotide monophosphate. The presence of this enzyme in the human placenta has been speculated on biochemical grounds, but direct cytochemical evidence has been lacking. Therefore, ultracytochemical localization of PDE activity was demonstrated in the human term placenta directly by electron microscopical enzymecytochemistry. Both cyclic AMP PDE and cyclic GMP PDE activity was observed on the syncytiotrophoblast, but subcellular localization differed in detail. Cyclic AMP PDE activity was positive both on the microvillous membrane and on the basal plasma membrane, while cyclic GMP PDE activity was confined to the microvillous membrane of the syncytiotrophoblast. These observations suggest that the syncytiotrophoblast may play an important role in cyclic nucleotide metabolism and that PDE may regulate nascent cyclic nucleotide in the syncytiotrophoblast.