Clinical experience of long-term transdermal treatment with nitric oxide donor for women with preeclampsia

Recent advances on the development of NO-releasing molecules (NORMs) for biomedical applications

Nitric oxide (NO) is an important biological messenger as well as a signaling molecule that participates in a broad range of physiological events and therapeutic applications in biological systems. However, due to its very short half-life in physiological conditions, its therapeutic applications are restricted. Efforts have been made to develop an enormous number of NO-releasing molecules (NORMs) and motifs for NO delivery to the target tissues. These NORMs involve organic nitrate, nitrite, nitro compounds, transition metal nitrosyls, and several nanomaterials. The controlled release of NO from these NORMs to the specific site requires several external stimuli like light, sound, pH, heat, enzyme, etc. Herein, we have provided a comprehensive review of the biochemistry of nitric oxide, recent advancements in NO-releasing materials with the appropriate stimuli of NO release, and their biomedical applications in cancer and other disease control.

Nitric Oxide in the Prevention of Pre-eclampsia (NOPE): A Double-Blind Randomized Placebo-Controlled Trial Assessing the Efficacy of Isosorbide Mononitrate in the Prevention of Pre-eclampsia in High-Risk Women

INTRODUCTION

Pre-eclampsia contributes to maternal and fetal morbidity and mortality all over the world. Endothelial dysfunction is postulated to be the crux of the pathogenesis. Recent meta-analysis of aspirin trials showed aspirin to be effective when started early in pregnancy (at ≤ 16-week gestation). We aimed to study the effect of low-dose prophylactic isosorbide mononitrate (ISMN) 20 mg/day on the incidence of hypertensive diseases in high-risk women receiving standard aspirin prophylaxis.

METHODS

Design: Randomized double-blind placebo-controlled parallel-arm superiority trial. Setting: Antenatal clinic of a tertiary teaching hospital, South India. Participants and methods: One hundred women fulfilling NICE guideline criteria for aspirin prophylaxis recruited at 12-16 weeks were randomized to receive either 20 mg/day of ISMN or placebo, in addition to 75 mg/day of oral aspirin from recruitment till delivery. Main outcome measure: Rate of hypertensive disorder of pregnancy (HDP). Sample Size: One hundred women (50 in each arm) to detect a decrease of HDP from 20% in the placebo group to 5% in the ISMN group with a power of 80% and at 0.05.

RESULTS

One hundred women (50 in each arm) participated and completed the trial. Intention to treat analysis of these 100 women showed that the groups were comparable in terms of age, BMI, parity, and vascular indices (such as mean arterial pressure, uterine artery pulsatility index, flow-mediated vasodilatation index, brachial-ankle pulse wave velocity, Ankle-Brachial Index, brachial arterial stiffness index, and ankle arterial stiffness index). The rate of hypertensive disorders (gestational hypertension, pre-eclampsia, or superimposed pre-eclampsia) was not significantly different between the groups (14/50, 28% in ISMN vs. 12/50, 24% in placebo group; p = 0.7). The mean gestational age at diagnosis of hypertensive disease (35.4 vs. 36 weeks, ISMN vs. placebo groups, p = 0.7) or the rate of severe disease (8/50, 16% in ISMN vs. 7/50, 14% in the placebo group; p = 0.9) did not differ significantly between the two groups. Stillbirths (1 vs. 2), NICU admission rates (18 vs. 10%), and neonatal mortality (2 vs. 2) were also similar between the groups.

CONCLUSION

The results of the randomized controlled trial of nitric oxide in the prevention of pre-eclampsia (NOPE) showed that in high-risk women receiving standard aspirin prophylaxis from less than 16 weeks, there is no significant reduction in the incidence of hypertensive disorders of pregnancy in the ISMN group, to the desired extent. There was no significant effect on the severity of disease, gestational age at diagnosis of disease or maternal-perinatal morbidity due to low-dose isosorbide mononitrate.

Nitric oxide-releasing molecules at the interface of inorganic chemistry and biology: a concise overview

The useful aspects of nitric oxide (NO) are nowadays widely known. Due to the need for this molecule in the maintenance of homeostasis, NO-releasing compounds are tested every year to optimize its levels in a patient suffering from low NO production. This manuscript is an update of some important historical concerns about nitrosyl complexes having the ability to act as NO-releasing compounds under the influence of different chemically modified environments. At present, the search for efficient and less harmful NO-releasing molecules at desirable targets and concentrations has gained considerable momentum in nitrosyl chemistry. Iron, ruthenium, and manganese nitrosyls have been investigated elitely to disentangle their electronic transition (excitation) under visible light to act as NO donors without harming the healthy cells of a target. There is much evidence supporting the increase of NO lability if amino acids are used as complexing ligands, the design of a reduction center close to an NO grouping, and the development of porphyrin system-based nitrosyl complexes. From the overall survey, it may be concluded that the desirable properties of such scaffolds need to be evaluated further to complement the biological milieu.

Effect of Transdermal Nitroglycerine on Doppler Velocity Waveforms of the Uterine, Umbilical and Fetal Middle Cerebral Arteries in Patients with Chronic Placental Insufficiency: A Prospective RCT

INTRODUCTION

Increase in Nitric Oxide (NO) may be important in vascular adaptation needed to accommodate increased uteroplacental blood flow as pregnancy advances. Hence, in certain conditions like Pregnancy Induced Hypertension (PIH) and Fetal Growth Restriction (FGR), NO donors may play an effective role in increasing uteroplacental perfusion. Transdermal route appears to be a safe and effective route.

AIM

To evaluate the effect of nitroglycerine patch on Doppler velocity waveforms of the uterine, umbilical and fetal middle cerebral arteries in patients with chronic placental insufficiency.

MATERIALS AND METHODS

A prospective randomized controlled clinical trial was conducted on eighty consecutive pregnant women with FGR with or without PIH and having evidence of altered waveform velocimetry in uterine, umbilical and fetal middle cerebral artery. They were divided into two groups- study and control group. Transdermal nitroglycerine patch (10 mg per 24 hours) was applied in study group for three consecutive days. Changes in various Doppler indices were noted after three days of patch application and compared between the two groups. Analysis was carried out using SPSS (Statistical Package for Social Studies) for Windows version 20.0 and online GraphPad software (Prism 5 for Windows) version 5.01.

RESULTS

A significant fall in the systolic and diastolic ratio (S/D), Pulsatility Index (PI) and Resistivity Index (RI) of the uterine (3.07±0.52, 1.04±0.14 and 0.54±0.10 respectively, p<0.001) and umbilical artery (3.73±3.30, 1.18±0.21and 0.64±0.07 respectively, p<0.001) was noted after three days of patch application. No such significant change was observed in the middle cerebral artery indices.

CONCLUSION

The therapeutic approach of NO donor administration via transdermal route in pregnant patients with chronic placental insufficiency, apparently improved both maternal and fetoplacental haemodynamics, thus may help in improving perinatal outcome.

S-Nitrosoglutathione improves haemodynamics in early-onset pre-eclampsia

AIMS

To determine the effects of in vivo S-nitrosoglutathione (GSNO) infusion on cardiovascular function, platelet function, proteinuria and biomarker parameters in early-onset pre-eclampsia.

METHODS

We performed an open-label dose-ranging study of GSNO in early-onset pre-eclampsia. Six women underwent GSNO infusion whilst receiving standard therapy. The dose of GSNO was increased incrementally to 100 μg min(-1) whilst maintaining blood pressure of >140/80 mmHg. Aortic augmentation index, aortic pulse wave velocity, blood pressure and maternal-fetal Doppler parameters were measured at each dose. Platelet P-selectin, protein-to-creatinine ratio and soluble anti-angiogenic factors were measured pre- and postinfusion.

RESULTS

Augmentation index fell at 30 μg min(-1) S-nitrosoglutathione (-6%, 95% confidence interval 0.6 to 13%), a dose that did not affect blood pressure. Platelet P-selectin expression was reduced [mean (interquartile range), 6.3 (4.9-7.6) vs. 4.1 (3.1-5.7)% positive, P = 0.03]. Soluble endoglin levels showed borderline reduction (P = 0.06). There was a borderline significant change in pre-to-postinfusion protein-to-creatinine ratio [mean (interquartile range), 0.37 (0.09-0.82) vs. 0.23 (0.07-0.49) g mmol(-1) , P = 0.06]. Maternal uterine and fetal Doppler pulsatility indices were unchanged.

CONCLUSIONS

In early-onset pre-eclampsia, GSNO reduces augmentation index, a biomarker of small vessel tone and pulse wave reflection, prior to affecting blood pressure. Proteinuria and platelet activation are improved at doses that affect blood pressure minimally. These effects of GSNO may be of therapeutic potential in pre-eclampsia, a condition for which no specific treatment exists. Clinical studies of GSNO in early-onset pre-eclampsia will determine whether these findings translate to improvement in maternal and/or fetal outcome.

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.

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.

[Color Doppler imaging and measurements of intraovarian and intrauterine vascularization on basal ultrasound examination in spontaneous ovulatory and anovulatory cycles]

BACKGROUND/AIM

Any organs functioning directly depends on vascularization. It applies also to the uterus and ovary which go through changes of vascularization during a menstruation cycle. The aim of this investigation was to determine differences in intrauterine and ovarian stromal arterioral blood flow on basal ultrasound examination (day 2-4) between spontaneous ovulatory and anovulatory cycles.

METHODS

This prospective clinical investigation included 205 patients divided into two groups: with ovulatory and with anovulatory cycles.

RESULTS

Resistance to ovarian arterioral stromal blood flow was significantly lower in the patients with ovulatory cycles (pulsatile index--PI 0.97 +/- 0.4 vs 1.93 +/- 1.37; p = 0.001737; and (resistance index - RI 0.55 +/- 0.12 vs 0.68 +/- 0.14; p = 0.040033). There. were no statistically significant differences in arcuate arterioral blood flow in the pateints with ovulatory and anovulatory cycles (PI 1.21 +/- 0.34 vs 61 +/- 0,61 p = 0.136161 and RI 0.64 +/- 0.11 vs 0.74 +/- 0.07; p = 0.136649). The patients with ovulatory cycles had lower uterine radial arterioral blood flow than the patients with anovulatory cycles (PI 1.001 +/- 0.22 vs 1.61 +/- 0.23 p = 0.007501 and RI 0.55 +/- 0.08 vs 0.71 +/- 0.12; p = 0,0460113). The patients with ovulatory cycles had lower subendometrial arterioral blood flow resistance (PI 0.69 0.19 vs 1.385 +/- 0.09; p = 0.00622 and RI 0.44 +/- 0.09 vs 0.65 +/- 0.02; p = 0.027458).

CONCLUSION

Color Doppler ultrasuond imaging and measurements of intrauterine and ovarian stromal arterioral blood flow on basal ultrasound examination (day 2-4), showed lower resistance to blood flow in ovulatory than in anovulatory cycles.

Isosorbide dinitrate and hydralazine hydrochloride: a review of efficacy and safety

In the USA alone, there are over 5,000,000 people diagnosed with heart failure. A disproportionate number of African-Americans are affected by this disease, with increased morbidity and mortality, yet they are tremendously under-represented in clinical trials. Several drugs have been approved for use in heart failure based on clinical trials, with percentages of African-American subjects as low as 1%. In the African-American Heart Failure Trial the use of BiDil, a drug combining isosorbide dinitrate and hydralazine hydrochloride, demonstrated a 43% decrease in overall mortality and a 39% decrease in first hospitalization. The combination consists of 20 mg of isosorbide and 37.5 mg hydralazine hydrochloride in a fixed dose that functions as a nitric oxide enhancer and an antioxidant, and helps to prevent tolerance to the prolonged use of nitrate. The hemodynamic effects of the combination drug in heart failure includes increased cardiac output. The US Food and Drug Administration approved the combination of isosorbide dinitrate based on the African-American Heart Failure Trial. Further clinical trials utilizing isosorbide dinitrate will hopefully determine the benefit of this combination in a larger population, including caucasians and other racial/ethnic groups.

Impaired uterine perfusion associated with metabolic disorders in women with polycystic ovary syndrome

BACKGROUND

Risk factors for cardiovascular disease, including chronic anovulation, obesity, hyperandrogenism, hyperinsulinemia, and dyslipidemia, are commonly observed in women with polycystic ovary syndrome (PCOS). We evaluated uterine perfusion and its correlation with clinical and biochemical parameters in women with PCOS.

METHODS

We performed a pulsed Doppler study on uterine arterial blood flow in 25 women with PCOS and 45 control women with regular menstrual cycles. PCOS was diagnosed based on oligomenorrhea, polycystic ovaries determined by means of ultrasonography, and elevated luteinizing hormone (LH)/follicle-stimulating hormone (FSH) ratio.

RESULTS

Women with PCOS had a significantly higher body mass index (BMI) and serum testosterone, and showed insulin resistance and dyslipidemia, including increased total cholesterol, triglyceride, low-density lipoprotein-cholesterol (LDL-C), and decreased high-density lipoprotein-cholesterol (HDL-C). The uterine arterial pulsatility index (PI) in women with PCOS was significantly higher than that in the control women during the follicular phase. The PI was correlated with BMI, LH/FSH ratio, or LDL-C/HDL-C ratio, whereas it was inversely correlated with the HDL-C level. Women with PCOS had reduced endometrial thickness and elevated uterine arterial PI in the luteal phase, in which implantation occurs.

CONCLUSIONS

Elevation of uterine arterial blood flow resistance is associated with risk factors for cardiovascular events. Furthermore, the impaired uterine perfusion in the luteal phase may cause endometrial dysfunction in women with PCOS.

Induction of localized differences in rat uterine radial artery behavior and structure during gestation

OBJECTIVES

The objectives of this study were to investigate differences in diameter and vasoconstriction of premyometrial versus uteroplacental radial arteries and to evaluate the contribution of nitric oxide (NO) to myogenic tone as a function of vessel location.

STUDY DESIGN

Radial arteries supplying either the myometrium or placenta were dissected from the uterus of pregnant rats. Constrictor responses to pressure elevation were studied before and after inhibition of endothelial NO synthase (eNOS).

RESULTS

Passive lumen diameters of premyometrial and proximal uteroplacental arteries were comparable and significantly smaller than those of distal uteroplacental vessels. High potassium- and pressure-induced responses were also similar in premyometrial and proximal but were virtually absent in distal uteroplacental segments. L-NNA enhanced pressure-induced tone, but was without effect in distal uteroplacental segments.

CONCLUSION

Gestational remodeling alters arterial structure and reactivity in a highly localized manner. During pregnancy, enhanced basal production of NO may be an important local mechanism for uterine blood flow regulation.

A study of the efficacy of cervical ripening with nitric oxide donor versus placebo for cervical priming before second-trimester termination of pregnancy

This was a double-blind randomized control study to evaluate the efficacy of cervical priming by nitric oxide donor before second-trimester induced abortion. One-hundred healthy women with a singleton pregnancy between 14 and 20 weeks of gestation were randomized into either 40 mg isosorbide mononitrate or placebo, given intravaginally 12 h before induction. This was followed by intravaginal misoprostol induction. The induction-abortion interval, abortion rate, side effects and the woman's acceptability of the priming agent were recorded. All women completed the study and there was no severe complication recorded. There was no significant difference in the induction-abortion interval and abortion rate between the two groups. Isosorbide mononitrate group reported significantly more side effects of headache. More than 90% of the women in both groups found the priming agent acceptable. The application of intravaginal nitric oxide donors prior to the prostaglandins induction did not significantly improve the second-trimester induced-abortion process.

The effect of isosorbide dinitrate, a donor of nitric oxide, on maternal cerebral blood flow in gestational hypertension and preeclampsia

OBJECTIVE

The purpose of this study was to investigate the effect of a nitric oxide donor on cerebral perfusion pressure and other blood flow index values in the maternal middle cerebral and basilar arteries.

STUDY DESIGN

Sublingual tablets of 5-mg isosorbide dinitrate were administered to 19 hypertensive pregnant patients. Doppler velocimetry of the middle cerebral and basilar arteries was obtained with a transcranial Doppler with the use of the transtemporal and suboccipital approach.

RESULTS

The mean (+/-SEM) flow velocity in the middle cerebral artery significantly decreased from a baseline of 65.9 +/- 3.1 cm/s to 55.2 +/- 2.2 and 52.0 +/- 2.1 cm/s at 10 and 20 minutes (P <.0001). Resistance area product insignificantly increased from a baseline of 2.0 +/- 0.1 before isosorbide dinitrate to 2.19 +/- 0.11 at 20 minutes. No significant changes were observed in the resistance and pulsatility indices in the middle cerebral artery. The cerebral perfusion pressure did not change significantly after isosorbide dinitrate (84.5 +/- 7.3, 80.8 +/- 6.6, and 78.5 +/- 5.0 mm Hg at 0, 10, and 20 minutes, respectively) nor did the cerebral blood flow index.

CONCLUSION

The results obtained demonstrate that cerebral perfusion pressure is unaltered by isosorbide dinitrate, despite significant changes in maternal blood pressure and in blood flow velocities in the middle cerebral artery.

Impaired uterine arterial blood flow in pregnant women with recurrent pregnancy loss

OBJECTIVE

This study was undertaken to evaluate uterine perfusion, which regulates uterine receptivity, in women with recurrent pregnancy loss.

METHODS

We evaluated the blood flow resistance in the uterine arteries of 104 pregnant women at 4 to 5 weeks' gestation by transvaginal pulsed Doppler ultrasonography (control group, n = 52; and recurrent pregnancy loss group, n = 52). Blood tests for antinuclear and antiphospholipid antibodies were also performed.

RESULTS

The uterine arterial pulsatility index in the recurrent pregnancy loss group was significantly higher than that in the control group. Women with antinuclear or antiphospholipid antibodies had an elevated pulsatility index in the uterine artery, which is prominent in women with recurrent pregnancy loss. Coagulopathy and vascular dysfunction caused by autoantibodies may impair uterine perfusion. However, the uterine arterial pulsatility index in the recurrent pregnancy loss group was significantly higher than that in the control group even among women without antinuclear antibodies or among women without antiphospholipid antibodies. This observation strongly suggests that the uterine artery pulsatility index may be an independent index for recurrent pregnancy loss.

CONCLUSIONS

The introduction of pulsed Doppler ultrasonography has provided the means for noninvasive evaluation of uterine impedance and may identify patients with recurrent pregnancy loss associated with impaired uterine perfusion.

A long-term transdermal nitric oxide donor improves uteroplacental circulation in women with preeclampsia

OBJECTIVE

To determine the effects of long-term transdermal administration (range, 4-30 days; mean +/- SD, 11.1+/-7.2 days) of isosorbide dinitrate, a nitric oxide donor, in preeclamptic women.

METHODS

We studied uterine and fetoplacental circulation of 12 preeclamptic women with oligohydramnios and an elevated pulsatility index in the uterine arteries.

RESULTS

Transdermal isosorbide dinitrate significantly suppressed the blood pressure of patients. Pulsed Doppler ultrasonography revealed that the average pulsatility index in the uterine arteries was significantly reduced by treatment with isosorbide dinitrate (P < .003). The average pulsatility index in the umbilical artery was also significantly reduced (P < .004). Furthermore, the size of the amniotic fluid pocket increased approximately 4-fold by treatment with isosorbide dinitrate.

CONCLUSIONS

Long-term transdermal administration of isosorbide dinitrate improves fetoplacental circulation and may be effective therapy for avoiding maternal hypertension and oligohydramnios in some preeclamptic women.

Effect of a nitric oxide donor on the ophthalmic artery flow velocity waveform in preeclamptic women

OBJECTIVE

To evaluate the effects of an antihypertensive agent on the orbital circulation of preeclamptic women.

METHODS

We studied the ophthalmic arteries of 10 healthy pregnant women and 10 women with severe preeclampsia by pulsed Doppler ultrasonography and evaluated the effect of transdermal isosorbide dinitrate, a nitric oxide donor, on preeclamptic women.

RESULTS

The average pulsatility index and resistive index were significantly lower, whereas the average end-diastolic velocity, time-averaged mean peak velocity, and peak ratio, which quantifies characteristic changes in the ophthalmic artery flow velocity waveform, were higher in preeclamptic women. Transdermal isosorbide dinitrate significantly reduced the average end-diastolic velocity (P < .05) and peak ratio of the ophthalmic artery (P < .01), whereas it did not significantly affect other indices.

CONCLUSIONS

Orbital circulation was altered in preeclamptic women. A nitric oxide donor affected orbital circulation. Peak ratio was a sensitive index for evaluating orbital circulation in preeclampsia.

Screening with a uterine Doppler in low risk pregnant women followed by low dose aspirin in women with abnormal results: a multicenter randomised controlled trial

OBJECTIVES

To assess whether systematic screening with an uterine artery Doppler in low risk pregnant women followed by the prescription of low dose aspirin in cases with abnormal results reduced the incidence of intrauterine growth restriction and pre-eclampsia.

DESIGN

A multicentre randomised trial.

POPULATION

3,317 low risk pregnant women. In the Doppler group, the uterine artery Doppler was performed between 20 and 24 weeks. Women with abnormal results received 100 mg of aspirin daily until the 35th week.

MAIN OUTCOME MEASURES

Intrauterine growth restriction was defined as birthweight below the tenth and the third centile according to gestational age. Pre-eclampsia was defined as hypertension associated with proteinuria > 0.5g/L.

RESULTS

Intrauterine growth restriction, whether defined by the third or tenth centile, did not differ significantly between the two groups (RR = 1.22 [0.73 - 2.04] and 1.18 [0.93 - 1.51] respectively). Screening with uterine artery Doppler did not affect birthweight or any of the criteria of perinatal morbidity. There was no effect on the incidence of pre-eclampsia (RR = 1.99 [0.97 - 4.09]) or hypertensive disorders. These results were the same for nulliparae and multiparae.

CONCLUSIONS

There is no justification for screening with uterine artery Doppler in a low risk population, even if abnormal results are followed by aspirin treatment and increased prenatal surveillance. Future studies must assess predictive tests that can be performed early in pregnancy and can identify populations at very high risk of pre-eclampsia and intrauterine growth restriction. Only when all of these conditions are fulfilled, aspirin or other treatments may prove its efficacy.

Pregnancy, vascular tone, and maternal hemodynamics: a crucial adaptation

The adaptation of vascular tone in early pregnancy precedes and probably triggers blood volume and cardiac output increase. Because the endothelium is known to regulate vascular smooth muscle action, the role of nitric oxide (NO) in the setting up of adequate uteroplacental and renal blood flow during normal pregnancy was investigated. The persistence of abnormally high uteroplacental resistance is a strong predisposing factor for intrauterine growth retardation and preeclampsia and can be screened by second trimester Doppler assessment of the uterine arteries. Current hypotheses suggested by experimental and clinical data concerning preeclampsia confirm the crucial role played by the endothelium and vascular tone adaptation. The analysis of these data leads to consider apart early-onset preeclampsia affecting pregnancies with growth retarded fetuses and associated with high vascular resistance. Lastly, NO donors seem to significantly decrease the impedance in the uteroplacental circulation and to improve fetoplacental hemodynamics assessed by Doppler measurements, and their therapeutic use in some forms of preeclampsia might be promising.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader will be able to summarize the events that regulate vascular tone in pregnancy, specifically the role of nitric oxide and other vasoactive prostaglandins in the regulation of vascular tone and to describe the various hypotheses concerning the mechanism and the mediators responsible for initiating endothelial damage in the various disorders of vascular tone in pregnancy.

Development of the placental villous tree and its consequences for fetal growth

Co-ordinated development of the fetal villous tree of the placenta is necessary for continued fetal growth and well-being. Before fetal viability, blood vessel development within the developing immature intermediate villi (IIV) is characterized by branching angiogenesis, such that the placenta expands to produce 10-16 generations of stem villi. Once fetal viability is attained, a developmental switch occurs to form large numbers of gas-exchanging terminal villi (TV) by non-branching angiogenesis in mature intermediate villi (MIV). Several growth factors, including vascular endothelial growth factor (VEGF), placenta growth factor (PlGF), angiopoietins, and angiostatins are produced within the villi and act locally, via their receptors, to control angiogenesis. Their relative contributions to placental vascular development are not fully understood at the present time. Severe early-onset intrauterine growth restriction (IUGR) is characterized by absent/reversed end-diastolic flow velocity (ARED) in the umbilical arteries, leading to fetal hypoxia, acidosis and a substantial rise in perinatal mortality and morbidity. The placentas from such cases show a deficit in peripheral villous development, which may be perpetuated by the effects of oxygen (delivered by maternal blood into the intervillous space) upon VEGF-directed angiogenesis, the so-called 'placental hyperoxia' theory of villous maldevelopment. Trophoblast apoptosis is a significant feature of early-onset IUGR and may explain poor flow-independent transfer of nutrients to the fetus. Finally, since transgenic mouse studies highlight the importance of trophoblast-derived transcription factors for placental villous (labyrinth) development, it is possible that the villous trophoblast controls the orderly development of the underlying mesoderm and blood vessels into the fetal villi.

Sublingual isosorbide dinitrate in the acute control of hypertension in patients with severe preeclampsia

The objective of this study was to evaluate the effectiveness of sublingual isosorbide dinitrate (ID) in the acute control of hypertension in patients with severe preeclampsia. A randomized, double-blind clinical trial with a preinclusion period of response to hydration and rest was performed in 60 patients with severe preeclampsia. The treatment group (30 patients) received 5 mg of sublingual ID, a dose that could be repeated on a second occasion. The control group consisted of 30 patients who received placebo. Both groups continued with rest and hydration during the study. Maternal blood pressure and fetal heart rate were measured in all patients every 10 min until 1 h was completed. Treatment was considered effective when the diastolic blood pressure could be reduced to between 80 and 100 mm Hg. ID was effective in 56.6% of the patients in the first 10 min after its administration and in 96. 6% from 40 to 60 min. In the treatment group the systolic and diastolic blood pressures dropped gradually from 171 +/- 13 and 113 +/- 8 mm Hg, respectively, to 136 +/- 14 and 87 +/- 9 mm Hg. In the placebo group, blood pressure was not reduced. There was no significant difference in fetal heart rate between both groups throughout the study. In conclusion, ID was shown to be effective in the acute control of hypertension in patients with severe preeclampsia, where high blood pressure persists after a period of rest and hydration.

Nitric oxide dysfunction in the pathophysiology of preeclampsia

Researchers disagree as to the importance of nitric oxide (NO) in preeclampsia. Many researchers have alluded to NO's possible primary or secondary role in the development of preeclampsia, but few have correlated the dysfunction of nitric oxide production with the other metabolic derangements seen in this condition. This paper will review the evidence that the primary dysfunction in preeclampsia is a relative deficiency of available NO (secondary to oxidative degradation) and an excess of peroxynitrite (ONOO(-)). The combination of a deficiency of NO and an increase in ONOO(-) can directly or indirectly initiate the vast majority of physiological and serological changes associated with preeclampsia, such as blood pressure, increased glomerular filtration rate, proteinuria, platelet dysfunction, increased thromboxane and endothelin, and a decrease in prostacyclin. Understanding the complex role of nitric oxide in this condition may explain why previous interventions have been unsuccessful and suggest possible strategies for prevention and treatment in the future.

Endothelin-mediated preeclampsia at high altitude

Preeclampsia is pregnancy-induced hypertension. The hypoxia at high altitude increases the incidence of preeclampsia. Endothelin is released in response to hypoxia and is associated with other hypertensive states at high altitude. Endothelin may play a major role in preeclampsia for individuals residing at high altitude. Endothelin antagonists may prove useful in the treatment of preeclampsia.