A study of the effect of nine monoamine oxidase (MAO) inhibitors on purified diamine oxidases (DAO) from human placenta and pig kidney is reported, together with the effect of 32 drugs commonly used in pregnancy on purified human placental diamine oxidase. Values of inhibitor constants, calculated from the slopes and intercepts of doublereciprocal plots are given, together with Δ G ° values for the enzyme-inhibitor interactions. From the results, we conclude that compounds once considered as specific monoamine oxidase inhibitors can no longer be thought of in this light, and that some of the drugs often used during pregnancy are potent in vitro inhibitors of human placental diamine oxidase.
