Nitric oxide donors: effects on fetoplacental blood flow

Placental blood flow sensing and regulation in fetal growth restriction

The mechanical force of blood flow is a fundamental determinant of vascular homeostasis. This frictional stimulation of cells, fluid shear stress (FSS), is increasingly recognised as being essential to placental development and function. Here, we focus on the role of FSS in regulating fetoplacental circulatory flow, both in normal pregnancy and that affected by fetal growth restriction (FGR).

The fetus is reliant on placental perfusion to meet its circulatory and metabolic demands. Failure of normal vascular adaptation and the mechanisms enabling responsive interaction between fetoplacental and maternal circulations can result in FGR. FSS generates vasodilatation at least partly through the release of endothelial nitric oxide, a process thought to be vital for adequate blood flow. Where FGR is caused by placental dysfunction, placental vascular anatomy is altered, alongside endothelial dysfunction and hypoxia, each impacting upon the complex balance of FSS forces.

Identifying specific mechanical sensors and the mechanisms governing how FSS force is converted into biochemical signals is a fast-paced area of research. Here, we raise awareness of Piezo1 proteins, recently discovered to be FSS-sensitive in fetoplacental endothelium, and with emerging roles in NO generation, vascular tone and angiogenesis. We discuss the emerging concept that activating mechanosensors such as Piezo1 ultimately results in the orchestrated processes of placental vascular adaptation. Piecing together the mechanisms governing endothelial responses to FSS in placental insufficiency is an important step towards developing new treatments for FGR.

Potential effects of transdermal nitric oxide donor on fetal growth restriction and oligohydramnios: A case report

Transdermal nitric oxide donor may be a relatively safe treatment strategy for fetal growth restriction and oligohydramnios due to placental insufficiency.

Does Pentaerytrithyltetranitrate reduce fetal growth restriction in pregnancies complicated by uterine mal-perfusion? Study protocol of the PETN-study: a randomized controlled multicenter-trial

BACKGROUND

Affecting approximately 10% of pregnancies, fetal growth restriction (FGR), is the most important cause of perinatal mortality and morbidity. Impaired placental function and consequent mal-perfusion of the placenta is the leading cause of FGR. Although, screening for placental insufficiency based on uterine artery Doppler measurement is well established, there is no treatment option for pregnancies threatened by FGR. The organic nitrate pentaerithrityl tetranitrate (PETN) is widely used for the treatment of cardiovascular disease and has been shown to have protective effects on human endothelial cells. In a randomized placebo controlled pilot-study our group could demonstrate a risk reduction of 39% for the development of FGR, and FGR or death, by administering PETN to patients with impaired uterine artery Doppler at mid gestation. To confirm these results a prospective randomized placebo controlled double-blinded multicentre trial was now initiated.

METHOD

The trial has been initiated in 14 centres in Germany. Inclusion criteria are abnormal uterine artery Doppler, defined by mean PI > 1.6, at 190 to 226 weeks of gestation in singleton pregnancies. Included patients will be monitored in 4-week intervals. Primary outcome measures are development of FGR (birth weight < 10th percentile), severe FGR (birth weight < 3rd centile) and perinatal death. Placental abruption, birth weight below the 3rd, 5th and 10th centile, development of FGR requiring delivery before 34 weeks` gestation, neonatal intensive care unit admission, and spontaneous preterm delivery < 34 weeks` and 37 weeks` gestation will be assessed as secondary endpoints. Patient enrolment was started in August 2017. Results are expected in 2020.

DISCUSSION

During the past decade therapeutic agents with possible perfusion optimizing potential have been evaluated in clinical trials to treat FGR. Meta-analysis and sub-analysis of trials targeting preeclampsia revealed ASS to have a potential in reducing FGR. Phosphodiesterase-type-5 inhibitors have recently been tested in a worldwide RCT for therapy of established FGR, failing to show an effect on neonatal outcome. The ongoing multicenter trial will, by confirming our previous results, finally provide a therapeutic option in cases at risk for FGR.

TRIAL REGISTRATION

DRKS00011374 registered at September 29th, 2017 and NCT03669185 , registered September 13th, 2018.

Comparison between transdermal nitroglycerin and sildenafil citrate in intrauterine growth restriction: effects on uterine, umbilical and fetal middle cerebral artery pulsatility indices

OBJECTIVES

To evaluate the effects of transdermal nitroglycerin (GTN) and sildenafil citrate on Doppler velocity waveforms of the uterine (UtA), umbilical (UA) and fetal middle cerebral (MCA) arteries in pregnancies with intrauterine growth restriction (IUGR).

METHODS

This was a prospective study of 35 singleton pregnancies (gestational age, 24-31 weeks) with IUGR and abnormal UtA and UA Doppler waveforms. We compared maternal arterial blood pressure and Z-scores of the pulsatility index (PI) of UtA, UA and fetal MCA before and after application of a transdermal GTN patch (average dose, 0.4 mg/h), oral sildenafil citrate (50 mg) or placebo. Statistical analysis was performed by ANOVA for paired samples.

RESULTS

There was a significant decrease in UtA-PI after application of GTN (21.0%) and sildenafil citrate (20.4%). A significant reduction in UA-PI was also observed for both GTN (19.1%) and sildenafil citrate (18.2%). There was no difference in UtA- and UA-PI when the GTN and sildenafil groups were compared. No changes in Doppler velocimetry were observed in the placebo group and no significant change in MCA-PI was observed in any group. Maternal arterial blood pressure decreased with administration of both GTN and sildenafil citrate in those with pre-eclampsia.

CONCLUSION

The use of transdermal GTN or sildenafil citrate in pregnancies with IUGR is associated with a significant reduction in both UtA and UA Doppler PI, as well as maternal arterial blood pressure. Neither drug affected the MCA-PI. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

The role of nitrates in the prevention of preeclampsia: an update

PURPOSE OF REVIEW

Defective nitric oxide synthesis and nitric oxide-mediated vasodilatation is widely documented in the pathophysiology of preeclampsia, a leading cause of maternal and perinatal morbidity and mortality worldwide. Several studies demonstrated the beneficial role of nitric oxide agents, especially glyceryl trinitrate and L-arginine in reducing the blood pressure and improving the uteroplacental blood flow velocities. However, there is insufficient evidence on the efficacy and safety of these agents in the prevention of preeclampsia and its complications, as there are very few randomized controlled trials with small number of women. The aim of this review is to summarize and evaluate the role of nitrates in the prevention of preeclampsia based on the available evidence in the literature till date and suggestions for future research.

RECENT FINDINGS

Supplementation with L-arginine and antioxidant vitamins reduced the incidence of preeclampsia in women at high risk of preeclampsia [P < 0.001, absolute risk reduction 0.17 (confidence interval 0.12-0.21)].

SUMMARY

On the basis of the recent evidence, nitric oxide agents may be beneficial in the prevention of preeclampsia. Randomized controlled trials initiated in the first trimester and using long-acting nitrates are needed in high-risk women to validate these findings.

Transdermal nitroglycerin in patients with severe pre-eclampsia with placental insufficiency: effect on uterine, umbilical and fetal middle cerebral artery resistance indices

OBJECTIVES

To evaluate the effect of transdermal nitroglycerin on Doppler velocity waveforms of the uterine, umbilical and fetal middle cerebral arteries in patients with severe pre-eclampsia.

METHODS

This was a prospective study of 30 singleton pregnancies (gestational age range: 24-31 weeks) with severe pre-eclampsia and abnormal uterine and umbilical artery Doppler waveforms. We compared maternal blood pressure as well as the resistance index (RI) and the pulsatility index (PI) of the uterine, umbilical and fetal middle cerebral arteries before and after application of a transdermal nitroglycerin patch (average dose 0.4 mg/h) for a period of 3 days. Intra-day comparisons before and after administration of nitroglycerin and a comparison between days 0 (no patch) and 3 after administration of the first dose of nitroglycerin were performed using ANOVA for paired samples.

RESULTS

A significant decrease in the PI and RI of the uterine (25.3 ± 4.9% and 21.2 ± 6.2%, respectively, P < 0.001) and umbilical (23.1 ± 6.9% and 19.7 ± 6.1%, respectively, P < 0.001) arteries was noted when comparing the first day without medication against the third day with the patch. No significant change in the PI and RI of the middle cerebral artery was observed. The mean arterial blood pressure decreased from 119.5 ± 4.5 mmHg to 114.8 ± 4.4 mmHg (P < 0.05).

CONCLUSION

The use of transdermal nitroglycerin in patients with severe pre-eclampsia is associated with a significant reduction in the RI and PI of the uterine and umbilical arteries, as well as of maternal blood pressure. Transdermal nitroglycerin does not affect the RI and PI of the fetal middle cerebral artery.

Sildenafil increases uterine blood flow in nonpregnant nulliparous women

This study investigated the effect of sildenafil on uterine volumetric blood flow (UVF) and vascular impedance in nonpregnant, nulliparous women. Fifteen women were randomized in a double-blind fashion to receive either placebo or sildenafil (25 or 100 mg) during the luteal phase of the menstrual cycle. Color Doppler ultrasound of both uterine arteries was performed at baseline and at 1 and 3 hours postdosing to calculate resistance index (RI) and UVF. Those who received sildenafil significantly increased UVF and decreased RI over the 3-hour monitoring period. When UVF responses to sildenafil were examined as a function of baseline UVF, a significant increase in UVF was observed in only those participants with higher baseline UVF. Overall, women in the luteal phase demonstrated a significant increase in UVF in response to sildenafil. However, this increase appears to be directly associated with basal UVF.

Acute Myocardial Infarction in Pregnant Women

Acute myocardial infarction (AMI) in pregnant women is a rare but potentially lethal occurrence that should be carefully managed, especially in consideration of cardiac conditions being a rising cause of maternal deaths. Risk factors for AMI occurrence, in addition to typical cardiac-related risk factors, include medical conditions such as (pre) eclampsia, blood transfusions, thrombophilia and postpartum infections. Being older, multigravida or in the third trimester of pregnancy is also associated with an increased risk. The pathophysiological causes underlying AMI in pregnancy are diverse but generally associated with the coagulative and physiological changes related to the pregnancy. The selection of diagnostic modality and treatment options require careful consideration for pregnancy-related changes as well as risk of harm to the patient and fetus. This paper serves to review available literature regarding an extensive range of management issues that directly impact on maternal and fetal outcomes. Key words: Myocardial infarction, Pregnancy complications, Obstetric labour complications

Acute myocardial infarction associated with pregnancy

Acute myocardial infarction (AMI) during pregnancy or the early post-partum period is rare but has been shown to be associated with poor maternal as well as fetal outcome. Major changes in both diagnosis and treatment of AMI in the nonpregnant patient have lead to improved outcome which may also affect pregnant patients. The purpose of this paper is to review available information related to the pathophysiology and clinical profile and provide recommendations for the diagnosis and management of AMI occuring during pregnancy and the early post-partum period.

Effects of oral l-arginine on the pulsatility indices of umbilical artery and middle cerebral artery in preterm labor

OBJECTIVE

The objective of the study was the estimation of the influence of oral supplementation with low-dose l-arginine on feto-placental circulation in women with threatened preterm labor.

STUDY DESIGN

Oral administration of 3g of L-arginine daily or placebo as a supplement to standard tocolytic therapy was tried in 70 women with threatened preterm delivery, randomly assigned to the L-arginine (n=37) or placebo (n=33) groups. Twenty-five and 20 completed the study, respectively. Doppler velocimetry of pulsatility indices (PI) of the umbilical (UA) and middle cerebral (MCA) arteries as well as pregnancy outcome and biochemical markers of nitric oxide synthesis (plasma amino acid and nitrite/nitrate levels, as well as 24 h nitrite/nitrate excretion with urine) were estimated.

RESULTS

Starting from the second week of therapy, the UA PI values were significantly lower in the L-arginine group than in the placebo group. Moreover, treatment with L-arginine caused a significant increase in MCA PI and cerebro-placental ratio (CPR) values. The changes in feto-placental circulation in the L-arginine group were not associated with any signs of increased nitric oxide synthesis.

CONCLUSION

Oral supplementation with low doses of L-arginine changed feto-placental blood flow distribution in patients with threatened preterm labor. The exact mechanism of L-arginine action on feto-placental circulation requires further investigation.

Nitric oxide in the human uterine cervix: endogenous ripening factor

The human uterine cervix can produce nitric oxide (NO), a free radical with an ultra-short half-life. The release of NO changes during pregnancy and is increased in early nonviable pregnancies compared to normal uncomplicated pregnancies. This review concentrates on the role of NO release in cervical ripening in pregnant women. Also some suggestions on future aspects are discussed.

Clinical use of nitric oxide donors and L-arginine in obstetrics

Nitric oxide (NO) is a free radical that plays a fundamental role in human physiology, being involved in the homeostasis of different functions. In obstetrics this molecule is determinant in the physiology of labor and cervical ripening; it possibly plays a fundamental role in the etiology of preeclampsia and intrauterine growth restriction, and it could also be utilized in view of its ability to induce smooth muscle relaxation. Several clinical trials have ascertained the ability of the topical application of NO donors to promote cervical ripening, and also labor induction. There is much less evidence on the use of NO donors in the vascular complications of pregnancy, either as prophylactics or therapeutic agents. Due to the capacity of NO to promote relaxation of smooth muscle, NO donors have been employed as tocolytics with performance similar to other agents. Moreover, although anecdotal, the experience of sudden uterine relaxation using NO donors in obstetric emergencies remains of great clinical value.

Randomized double-blind placebo-controlled trial of transdermal nitroglycerin for preterm labor

OBJECTIVE

Despite advances in perinatal medicine, the incidence of preterm birth continues to increase. The primary goal of tocolytic therapy is to reduce neonatal morbidity and mortality. While studies have demonstrated a prolongation of pregnancy, no tocolytic has been shown to improve neonatal outcomes. The objective of this randomized placebo-controlled trial was to determine the effect of transdermal nitroglycerin on neonatal outcomes in women who present in preterm labor.

STUDY DESIGN

We randomized 153 women in labor between 24 and 32 weeks to receive either transdermal nitroglycerin or placebo patches. The primary outcome was a composite of neonatal morbidity (chronic lung disease, intraventricular hemorrhage, periventricular leukomalacia, necrotizing enterocolitis) and mortality. Secondary outcomes included birth within 48 hours, birth before 28, 34, and 37 weeks, number of doses of antenatal corticosteroids received, side effects, and adverse events.

RESULTS

Infants born to transdermal nitroglycerin treated mothers (n = 74) had a statistically significantly reduced composite outcome compared to placebo treated mothers (n = 79) (relative risk 0.29 [95% confidence interval 0.08, 1.00] [p = 0.048]; risk difference -0.10 [95% confidence interval -0.19, -0.01); number needed to treat 10 [95% confidence interval 5, 100]). Birth prior to 28 weeks was reduced (relative risk 0.50, 95% confidence interval 0.23, 1.09). Transdermal nitroglycerin caused significantly more maternal side effects (relative risk 1.41, 95% confidence interval 1.06, 1.86).

CONCLUSION

Transdermal nitroglycerin may reduce neonatal morbidity and mortality as a result of decreased risk of birth before 28 weeks.