LETTERS to the EDITOR

Endothelin in umbilical artery vasospasm

Objectives: To evaluate the relationship of endothelin 1 (ET-1) and leptin concentrations in women and newborns following a pregnancy complicated with intrauterine growth restriction (IUGR). Methods: Twenty-five women with a pregnancy complicated with IUGR at 19 different gestational ages were matched with women with uncomplicated pregnancies. Blood samples from the umbilical artery and maternal peripheral venous circulation were collected at delivery, and ET-1 and leptin levels were determined from the blood samples. Data relating to obstetric complications (e.g., pregnancy-induced hypertension), delivery (e.g. mode, birth weight, signs of intrapartum fetal distress, and Apgar scores) were also recorded. Results: Mean maternal ET-1 (13.4±6.2–9.9±2.9 pmol/l) and mean fetal ET-1 (14.5±4.2–11.7±3.1 pmol/l) concentrations were significantly higher when women had experienced pregnancies complicated with IUGR than when they had had normal pregnancies. Mean fetal leptin concentration was significantly lower in the study group (6.8±2.2 ng/ml) than in the control group (10.6±3.6 ng/ml (P<0.05). However, fetal leptin per kilogram of fetal weight was not significantly different in the study group (3.16±1.18 ng/ml) than in the control group (3.23±0.96 ng/ml) (P>0.05, paired t-test). However, a statistically significant correlation was observed between fetal leptin concentrations per kilogram of fetal weight and fetal endothelin concentrations in pregnancies complicated with IUGR (r=0.546; P<0.05). Conclusions: These results suggest the intertwined roles of ET-1 and leptin in the pathophysiology of IUGR. Further studies concerning interaction between these peptides in different pregnancy conditions may provide important information about the actions of ET-1 and leptin on fetal growth.

Objective: To study plasma concentrations of endothelin (ET), lipidhydroperoxides (LOOH), glutathione peroxidase (GSHpx) and fibronectin in relation to abnormal umbilical artery velocimetry. Study design: Plasma concentrations of ET, LOOH, GSHpx and fibronectin were measured in fetal and maternal venous blood in: (i) a control group (n=10); (ii) in pregnancies complicated by intrauterine growth retardation (IUGR) (n=6) or preeclampsia (n=5) with positive end diastolic flow; and in (iii) pregnancies complicated by absent or reversed end diastolic (ARED) flow in the umbilical artery (n=18). All children were delivered by primary caesarean section. Results: The significantly highest maternal and fetal ET concentrations were found in plasma collected in pregnancies complicated by ARED flow in the umbilical artery. Maternal fibronectin levels were significantly raised in the ARED flow group. Maternal plasma ET levels were lowest in pregnancies complicated by IUGR. The maternal and fetal plasma concentrations of LOOH and GSHpx did not differ significantly between the groups. Conclusion: Abnormal Doppler velocimetry, especially ARED flow is associated with elevated maternal and fetal plasma levels of ET. The exact mechanism causing the placental vasoconstriction is unknown yet, but oxidative stress seems not to be involved.

The endothelins (ETs) are potent vasoconstrictor peptides that bind to two distinct receptors, ET_A and ET_B. This study compares the localization of ET_A and ET_B receptors in placentae complicated by intrauterine growth retardation (IUGR) and abnormal umbilical Doppler waveform, gestationally matched controls, fetuses that were small for gestational age (SGA), and normal term placentae. Quantitative autoradiography was performed using ET_A and ET_B subtype-selective ligands. Both ET_A and ET_B receptors were expressed in the human placenta. Gestational and fetal size effects on the receptor density within stem villi were found, but no effect of abnormal placental blood flow could be demonstrated. A distinct spatial distribution of receptor subtypes within the placenta was observed. Smooth muscle cells expressed both receptors with ETA expression predominant in the proximal regions of the villous tree and ET_B abundant in the periphery and decidua. Both receptors were also expressed at lower density on paravascular stromal cells in stem villi. Although these data do not demonstrate aberrant localization of ET receptors in IUGR and SGA placentae, the spatially distinct distribution of ET receptors in the human placenta suggests that ETs play a role in modulation of placental blood flow.

Computerized microscope morphometry was used to study cross sections from the vessels of the umbilical cord in placentas of patients with intrauterine growth retardation (IUGR) that displayed either normal or abnormal umbilical arteries (UA) Doppler flow velocity waveforms (FVW). Cords from 63 eutrophic fetuses with normal Doppler (controls), 47 IUGR fetuses with normal Doppler and 32 IUGR fetuses with abnormal Doppler underwent morphometric analysis using a highly optimized microscope environment (HOME) and “CordHOME” software. IUGR with an accompanying normal Doppler versus control showed a reduction of Wharton jelly and both the total and lumen vein areas. IUGR with an accompanying pathological Doppler showed a comparable reduction in wall thickness and areas of every vessel. These findings indicate that the hypoplastic umbilical vessels are associated with an increase in placental vascular resistance that may be the consequence of underdevelopment in response to a chronic reduction in placental blood flow.

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. 8.0 ± 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.

The aim of this study was to measure plasma concentrations of total nitrites, as an index of nitric oxide (NO) synthesis, in the fetal circulation of normal pregnancies and in pregnancies complicated by intrauterine growth restriction. Plasma was prepared from umbilical venous blood collected from 13 placentae from normal pregnancies and 11 pregnancies complicated by intrauterine growth restriction. Plasma NO concentrations were determined using the Greiss reaction by measuring combined oxidation products of NO, plasma nitrite (NO₂⁻) and nitrate (NO₃⁻) after reduction with nitrate reductase. Significantly higher NO₂⁻ concentrations were found in umbilical venous plasma in the group complicated by intrauterine growth restriction compared to the control group (65.6 μmol/l versus 28.7 μmol/l, P<0.001). These results support the hypothesis that increased NO production may be a compensatory response to improve blood flow in the placenta and/or may play a role in limiting platelet adhesion and aggregation.