PLACENTAL TRANSPORT OF LEUCINE AND LYSINE IS REDUCED IN INTRAUTERINE GROWTH RESTRICTION

Intrauterine growth restriction (IUGR) is characterized by a reduction in fetal plasma concentrations of a number of essential amino acids. Whether this is caused by impaired placental transport is unknown. We studied transport of leucine and lysine in syncytiotrophoblast microvi llous (MVM) and basal membrane (BM) vesicles isolated from uncomplicat ed (control) and IUGR pregnancies. In addition, we investigated the po ssibility that leucine uptake is stimulated by an outwardly directed g lycine gradient. Uptake of H-3-L-lysine (0.1 mu M) and H-3-L-leucine ( 0.25 mu M) was studied at 37 degrees C using rapid filtration techniqu es. In IUGR, mediated uptake of lysine was reduced by 44% (p < 0.05) i n BM and uptake of leucine was lower in both MVM (-46%, p < 0.05) and BM (-38%, p < 0.05) compared with control vesicles. Intravesicular gly cine (2 mM) increased the uptake of leucine by 98% in MVM (p < 0.05). These data suggest that the activity of placental transporters for cat ionic and neutral amino acids is reduced in IUGR. We speculate that a reduced glycine gradient in the placenta in IUGR, due to reduction in system A activity, will impair leucine transport to the fetus, providi ng an additional mechanism for reduced placental transport of leucine in IUGR.