Placental Perfusion – A Human Alternative

Foetal growth and development is extremely dependent on placenta functionality, as the major role of the placenta is to exchange oxygen, nutrients, hormones and waste products between the mother and the foetus. In addition, the placenta has an important role in hormone synthesis and metabolism of compounds that regulate and maintain pregnancy (Ahokas and Anderson, 1987). The placenta develops from embryonic tissue and by the end of the third gestation week embryonic blood circulates through the capillaries of the villi (Khong and Pearce, 1987). The barrier function of the placenta membrane depends on molecular size, polarity, lipid solubility and protein binding of the substances. Both active transport mechanisms and facilitated transport have been described (Syme et al., 2004). Substances able to cross the placenta have the potential to cause adverse effects directly on foetal development or placenta function. Substances not able to cross the placenta may harm the foetus through effects on the mother, e.g. toxicity. The first evidence of reproductive toxicity caused by a foetal exposure from maternal intake was the thalidomide disaster in 1957-1961. Pregnant women from approximately 46 countries worldwide were prescribed thalidomide as a safe sedative. Given between the 34th and 50th day of pregnancy, thalidomide may exert teratogenic effects seen as skeletal malformation especially of the limbs. These malformations were reported in more than 10,000 babies who survived the exposure. When investigated further, the mechanism of action was specific to humans, but was later confirmed in a second animal species. As a result of this disaster the demands on testing of drugs to be used during pregnancy were increased (Botting, 2002; Brent, 2004) . In the early 1970s it was reported that prenatal alcohol exposure can cause mental retardation, facial malformations, prenatal and/or postnatal growth retardation (Riley and McGee, 2005; West and Blake, 2005). In 1971 the effect of the synthetic nonsteroidal estrogen diethylstilbestrol (DES) on the reproductive system became evident. The drug was prescribed to prevent misPlacental Perfusion – A Human Alternative