In Vitro Production of Diamine Oxidase by the Perfused Human Placenta1

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Abstract
Diamine oxidase (DAO) activity was measured in the "amniotic fluid" and in the fetal and maternal circulations during in vitro perfusions of human placentas. The perfusing fluid consisted of a balanced protein-free electrolyte solution. There was a continuous rise in DAO activity in the maternal circulation with relatively little change in enzyme titers in the "amniotic fluid" and fetal circulation. These data indicated that the integrity of the maternal and fetal circulations was maintained during the period of perfusion. The DAO content of the perfused placentas after replacement of the initial maternal perfusate with fresh fluid was similar to that obtained in a series of control unperfused human placentas despite the fact that large amounts of DAO were removed during the perfusion. This demonstrates a net gain in enzyme activity during the perfusions and indicates that the perfused human placenta is capable of actively producing DAO in vitro. The presence of a factor in the fetal circulation affecting DAO production by the perfused placenta in vitro was suggested by the lowered placental content of DAO after both the initial fetal and the maternal perfusate were replaced with fresh fluid. The absence of surrounding decidua in the placental preparations resulted in the passage of only small amounts of DAO activity into the "amniotic fluid" during the perfusion.