Histochemical studies on human placental and chorionic monoamine oxidase.

A new coupled peroxidation method for detection of monoamine oxidase was applied to human chorionic and placental tissues of various weeks of gestation. With this new method, the precise localization of monoamine oxidase activity could be determined and the two isotypes of the enzyme could be identified using selective inhibitors. Significant monoamine oxidase activity was observed in syncytiotrophoblasts of fine villi and budding villi. Monoamine oxidase activity in chorionic and placental tissues remained similar in intensity and localization throughout pregnancy. Only one type of monoamine oxidase, type A, was found in the placenta. The functional role of monoamine oxidase is discussed.