Human placental norepinephrine transporter mRNA: expression and correlation with fetal condition at birth.

The purpose of this study was to determine the primary form of human placental norepinephrine transporter (hNET) mRNA expressed in the human placenta and to compare the level of expression in normal pregnancies and in pregnancies complicated by drug exposure or other forms of physiological derangement. We used the hNET cDNA to measure RNA extracted from placenta and examined placental RNA following complicated and uncomplicated pregnancies. To compare transporter expression and its relation to fetal condition at birth, umbilical arterial plasma catecholamine levels, umbilical arterial blood gases and placental transporter mRNA level were compared by linear regression analysis. Uncomplicated pregnancies had a higher level of placental norepinephrine transporter mRNA than complicated pregnancies. An inverse relationship between umbilical cord norepinephrine level and transporter expression was demonstrated. We conclude that placental transporter expression represents an important and newly described metabolic function of the placenta. Placental catecholamine clearance mediated via the placental NET may be important in the pathophysiology of disorders associated with placental dysfunction, impaired placental blood flow or intrauterine growth retardation. This may also explain the adverse effects of drugs, such as cocaine, which block catecholamine transport.