To study the concentrations of endothelin-1 (ET-1) and its precursor,
big ET-1, in samples of amniotic fluid, fetal urine, umbilical arteria
l and venous blood, retroplacental blood and maternal uterine and brac
hial venous blood obtained from normal and preeclamptic women. Samples
were collected from 31 healthy pregnant women (16 in labor and 15 und
ergoing elective cesarean section) and 35 preeclamptic women (9 in lab
or and 26 undergoing cesarean section). Big ET-1 and ET-1 were measure
d 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 th
e 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 signific
antly higher on the fetal side (i.e., in the umbilical vein and amniot
ic fluid) than in maternal blood, but in these sampling locations ther
e was no difference between the normal pregnancy and preeclampsia grou
p. 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 pre
eclamptic group. ET-1 was significantly higher in amniotic fluid than
in the first neonatal urine of corresponding pregnancies (15.0 +/- 2.0
vs. 8.0 +/- 2.9 pmol/l, P < 0.05). The ET-1 and big ET-1 concentratio
ns are significantly higher in fetal plasma and amniotic fluid than in
maternal plasma, indicating increased endothelin converting enzyme ac
tivity and increased ET-1 production in utero. The elevated ET-1 conce
ntration in maternal blood in preeclamptic compared with normal pregna
nt women and the negative correlation between ET-1 in the umbilical ve
in and birth weight suggest that ET-1 plays a pathophysiological role
in preeclampsia and other conditions with intrauterine growth restrict
ion.