Fetal vascular atrial natriuretic peptide receptors in human placenta: alteration in intrauterine growth retardation and preeclampsia

Instability and frequency-domain variability of heart rates in fetuses with or without growth restriction affected by severe preeclampsia

This study investigated how the instability and frequency-domain variability in heart rates differ between fetuses affected only by severe preeclampsia and fetuses affected by both severe preeclampsia and growth restriction. From their antepartum fetal heart rates and those of control fetuses, the very short-term intermittency (C1alpha) and the spectral powers were calculated to evaluate the instability and frequency-domain variability, respectively. The fetuses affected only by severe preeclampsia showed abnormally high C1alpha and low- and high-frequency power. The fetuses affected by severe preeclampsia and growth restriction showed even higher C1alpha than that of the fetuses affected by severe preeclampsia and abnormally reduced low-frequency power. Conclusively, when compared to the heart rates of fetuses affected only by severe preeclampsia, the heart rates of fetuses affected by severe preeclampsia and growth restriction showed a greater abnormal instability and an abnormally reduced variability at low-frequency range.

Intrauterine growth restriction with absent end-diastolic flow velocity in the umbilical artery is associated with maldevelopment of the placental terminal villous tree

OBJECTIVE

Our purpose was to evaluate the structure of placental terminal villi and their capillaries in pregnancies complicated by intrauterine growth restriction with absent end-diastolic flow velocity in the umbilical artery.

STUDY DESIGN

Glutaraldehyde-perfusion-fixed villous tissue and a plastic cast of the vessels in at least two cotyledons were prepared from 10 cases with intrauterine growth restriction and 9 gestational age-matched control placentas. The structure and dimensions of 20 terminal capillary loops per cast were determined by scanning electron microscopic examination, and their appearances were correlated with the peripheral villi of the perfusion-fixed villous tissue.

RESULTS

Capillary loops in the growth-restricted cases were sparse in number and significantly longer than in the control cases (218 microns [72] vs 137 microns [30], mean and SD, p < 0.05). They exhibited fewer branches (4.0 [1.9] per loop vs 6.1 [2.2], p < 0.05) and a majority of loops were uncoiled (79% vs 18%, p < 0.05). The villous tissues from the growth-restricted cases demonstrated elongated villi, consistent with the cast findings. The trophoblast surface was wrinkled and in some areas covered by fibrin plaques.

CONCLUSIONS

The terminal villous compartment of the placenta appears to be maldeveloped in preterm intrauterine growth restriction pregnancies where absent end-diastolic flow velocity is demonstrated in the umbilical artery before delivery. These findings are consistent with an increase in fetoplacental vascular impedance at the capillary level and may account for the impaired gas and nutrient transfer in this disorder.

Nitric oxide concentrations are increased in the feto-placental circulation in 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 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 mumol/1, 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.

Atrial natriuretic peptide counteracts the vasoconstrictor effects of 5-hydroxytryptamine, U46619 and endothelin-1 in the human umbilical artery

A role for atrial natriuretic peptide (ANP) in maintaining low vascular resistance within the fetoplacental circulation was investigated using isolated strips of human umbilical artery (HUA). Physiological levels of ANP significantly reduced the isometric contractile response of the HUA to U46619 (a stable thromboxane A2 mimetic), to 5-hydroxytryptamine and to endothelin-1, though no effect on agonist sensitivity could be demonstrated. These data suggest that ANP may modify vascular tone in vivo thereby counterbalancing several humoral factors which act to increase vascular resistance within the fetoplacental circulation.