Endothelin-1 and big endothelin-1 levels in normal term pregnancy and in preeclampsia.

To study the concentrations of endothelin-1 (ET-1) and its precursor, big ET-1, in samples of amniotic fluid, fetal urine, umbilical arterial and venous blood, retroplacental blood and maternal uterine and brachial venous blood obtained from normal and preeclamptic women. Samples were collected from 31 healthy pregnant women (16 in labor and 15 undergoing elective cesarean section) and 35 preeclamptic women (9 in labor and 26 undergoing cesarean section). Big ET-1 and ET-1 were measured by radioimmunoassay and the ET-1 to big ET-1 ratios were calculated. In preeclamptic women there was a significant elevation of ET-1 in the maternal brachial and uterine veins and of big-ET-1 in the brachial vein. The ET-1 concentrations and the ET-1/big ET ratios were significantly higher on the fetal side (i.e., in the umbilical vein and amniotic fluid) than in maternal blood, but in these sampling locations there was no difference between the normal pregnancy and preeclampsia group. A significant negative correlation (r = -0.67, P < 0.01) was found between plasma ET-1 in the umbilical vein and birth weight in the preeclamptic group. ET-1 was significantly higher in amniotic fluid than in the first neonatal urine of corresponding pregnancies (15.0 +/- 2.0 vs. 3.0 +/- 2.9 pmol/l, P < 0.05). The ET-1 and big ET-1 concentrations are significantly higher in fetal plasma and amniotic fluid than in maternal plasma, indicating increased endothelin converting enzyme activity and increased ET-1 production in utero. The elevated ET-1 concentration in maternal blood in preeclamptic compared with normal pregnant women and the negative correlation between ET-1 in the umbilical vein and birth weight suggest that ET-1 plays a pathophysiological role in preeclampsia and other conditions with intrauterine growth restriction.