Anti-hypertensive therapy and the feto-placental circulation: effects on umbilical artery resistance

Fetoplacental vascular effects of maternal adrenergic antihypertensive and cardioprotective medications in pregnancy

Maternal cardiovascular diseases, including hypertension and cardiac conditions, are associated with poor fetal outcomes. A range of adrenergic antihypertensive and cardioprotective medications are often prescribed to pregnant women to reduce major maternal complications during pregnancy. Although these treatments are not considered teratogenic, they may have detrimental effects on fetal growth and development, as they cross the fetoplacental barrier, and may contribute to placental vascular dysregulation. Medication risk assessment sheets do not include specific advice to clinicians and women regarding the safety of these therapies for use in pregnancy and the potential off-target effects of adrenergic medications on fetal growth have not been rigorously conducted. Little is known of their effects on the fetoplacental vasculature. There is also a dearth of knowledge on adrenergic receptor activation and signalling within the endothelium and vascular smooth muscle cells of the human placenta, a vital organ in the maintenance of adequate blood flow to satisfy fetal growth and development. The fetoplacental circulation, absent of sympathetic innervation, and unique in its reliance on endocrine, paracrine and autocrine influence in the regulation of vascular tone, appears vulnerable to dysregulation by adrenergic antihypertensive and cardioprotective medications compared with the adult peripheral circulation. This semi-systematic review focuses on fetoplacental vascular expression of adrenergic receptors, associated cell signalling mechanisms and predictive consequences of receptor activation/deactivation by antihypertensive and cardioprotective medications.

Magnesium Sulfate-Mediated Vascular Relaxation and Calcium Channel Activity in Placental Vessels Different From Nonplacental Vessels

Background

Magnesium sulfate (MgSO₄) has been used as a common therapy for preeclampsia and eclampsia for many years. MgSO₄ decreases peripheral vascular resistance so as to reduce maternal blood pressure. Whether placental blood vessels react to MgSO₄ in the same patterns as that in maternal vessels is largely unknown.

Methods and Results

This study compared placental vessels (PV) versus nonplacental vessels (non‐PV) in human and animal models. MgSO₄‐caused vascular dilation was significantly weaker in PV than that in non‐PV. Prostaglandin I₂ synthetase affected MgSO₄‐mediated vasodilatation in PV, not in umbilical vessels, while cyclooxygenase did not influence MgSO₄‐induced relaxation in both PV and non‐PV. Mg²⁺‐caused vasodilatation was mainly through calcium channels. In PV, calcium channel activities were significantly weaker in PV than that in non‐PV. Relative mRNA expression of CACNA1D,CACNB2, and CACNB3 was significantly higher in PV than those in umbilical vessels, despite the fact that the expression of CACNA1F was less in PV. The contractile phenotype of smooth muscle cell marker (CALD1) was less and the synthetic phenotype (MYH10) was more in PV than that in UV.

Conclusions

These results demonstrated that PV were characterized by much weaker responses to MgSO₄ compared with nonplacental vessels. The difference was related to weaker calcium channel activity and minor contractile phenotype smooth muscle cells in PV, providing important information for further understanding treatments with MgSO₄ in preeclampsia.

The effect of loading dose of magnesium sulfate on uterine, umbilical, and fetal middle cerebral arteries Doppler in women with severe preeclampsia: A case control study

SYNOPSIS IV MgSO4 administration in women with severe preeclampsia resulted in a decrease in umbilical artery, uterine artery, and fetal middle cerebral artery Doppler indices.

OBJECTIVE

To evaluate Doppler parameters of the umbilical artery (UmA), uterine artery (UA), and fetal middle cerebral artery (MCA) before and after MgSO4 administration in women with severe preeclampsia.

METHODS

A case control study included 100 pregnant women with severe preeclampsia. Umbilical artery, uterine artery, and fetal middle cerebral artery Doppler were measured before and 20 minutes after intravenous administration of 6 g of magnesium sulfate.

RESULTS

There was a significant difference between maternal systolic blood pressure (173.20 ± 22.72 vs. 156.60 ± 19.18), diastolic blood pressure (109.60 ± 9.14 vs. 101.90 ± 10.05), and heart rate (80.52 ± 11.52 vs. 88.48 ± 12.08) before and after administration of MgSO4 in the studied patients (p value < 0.001). There was a significant difference between umbilical artery, middle cerebral artery, and uterine artery Doppler parameters before and after administration of MgSO4 in the studied patients (p value < 0.001). There was no significant difference between umbilical artery/middle cerebral artery with regard to RI and PI. However, there was significant difference with regard to the S/D ratio (p value < 0.001). The decrease in the values of Doppler parameters before and after administration of MgSO4 was more in the middle cerebral artery than in the umbilical artery.

CONCLUSION

Intravenous administration of magnesium sulfate in pregnant women with severe preeclampsia resulted in a decrease in umbilical artery, uterine artery, and fetal middle cerebral artery Doppler indices with reduced resistance to blood flow in these vessels.

Maternal hypertension, medication use, and hypospadias in the National Birth Defects Prevention Study

OBJECTIVE

To investigate whether antihypertensive classes and specific medications in early pregnancy increase the risk of severe hypospadias and to assess prior associations detected for late-treated and untreated hypertension in the National Birth Defects Prevention Study.

METHODS

Using telephone interviews from mothers of 2,131 children with severe hypospadias and 5,129 nonmalformed male control children for 1997-2009 births in a population-based case-control study, we estimated adjusted odds ratios (ORs) and 95% confidence intervals (CIs) with multivariable logistic regression. We adjusted P values to account for multiple testing.

RESULTS

Forty-eight (2.3%) case and 70 (1.4%) control mothers reported early pregnancy antihypertensive treatment, 45 (2.1%) case and 31 (0.6%) control mothers reported late treatment, and 315 (14.8%) case and 394 (7.7%) control mothers reported untreated hypertension. Selective β-blockers, centrally acting agents, renin-angiotensin system-acting agents, diuretics, and specific medications, methyldopa and atenolol, were not associated with hypospadias. Nonselective β-blockers (adjusted OR 3.22, 95% CI 1.47-7.05) were associated with hypospadias; however, P values adjusted for multiple testing were not statistically significant. We confirmed prior findings for associations between hypospadias and untreated hypertension (adjusted OR 2.09, 95% CI 1.76-2.48) and late initiation of treatment (adjusted OR 3.98, 95% CI 2.41-6.55). The increased risks would translate to severe hypospadias prevalences of 11.5, 17.7, and 21.9 per 10,000 births for women with untreated hypertension, nonselective β-blocker use, and late initiation of treatment, respectively.

CONCLUSION

Our study suggests a relationship between hypospadias and the severity of hypertension.

LEVEL OF EVIDENCE

II.

α-Methyldopa-induced hepatitis during the postpartum period

A 34-year-old woman, with a history of pre-eclampsia, was diagnosed with α-methyldopa-induced hepatotoxicity, after she presented with severe jaundice and hepatitis 8 weeks following delivery. Laboratory investigations and liver biopsy ruled out other causes of hepatitis. She continued to improve clinically after cessation of α-methyldopa, and was discharged 10 days after admission. This case report emphasises that it may not be possible to predict which patients may develop α-methyldopa-induced hepatitis, hence regular monitoring of liver function tests during treatment should be implemented.

Effect of the loading dose of magnesium sulfate (MgSO4) on the parameters of Doppler flow velocity in the uterine, umbilical and middle cerebral arteries in severe preeclampsia

OBJECTIVE

To evaluate Doppler velocimetry parameters (resistance index [RI], pulsatility index [PI] and systolic/diastolic [S/D] ratio) of maternal-fetal circulation before and after magnesium sulfate administration in pregnant women with severe preeclampsia.

METHODS

A prospective observational cohort analysis of 40 women with severe preeclampsia was performed. Doppler ultrasonography scans were performed before and 20 minutes after intravenous administration of magnesium sulfate. Maternal parameters such as heart rate, and systolic, diastolic and mean arterial pressure were recorded. Doppler flow velocity parameters (RI, PI and S/D ratio) were evaluated in the uterine, umbilical and middle cerebral arteries. The different mean values obtained before and after magnesium sulphate were analyzed using the paired t-test.

RESULTS

There was a statistically significant increase in mean maternal heart rate and a statistically significant decrease in systolic, diastolic and mean maternal blood pressure before and after administration of magnesium sulphate (p < 0.001). Resistance index decreased in the umbilical (p = 0.003; 95% CI: 0.008 - 0.03) and middle cerebral artery (p = 0.001; 95% CI: 0.01 - 0.05) and in both uterine arteries. Likewise, there was a significant reduction in the PI and S/D ratio in all the arteries assessed.

CONCLUSIONS

Maternal administration of intravenous magnesium sulfate in preeclampsia leads to an increase in maternal heart rate and a decrease in systolic, diastolic and mean arterial blood pressure. A reduction in the resistance index, pulsatility index and S/D ratio was recorded in the uterine, umbilical and cerebral arteries.

[Pregnancy hypertension]

Hypertension occurs in 6-8% of pregnancies, preeclampsia in 2%, found to be "severe" in 0.6%. Preeclampsia remains a major cause of foetal, and even maternal, mortality. Two different aspects are described: "maternal" preeclampsia is related to pre-existent vascular lesions in the mother, "placental" preeclampsia is due to a primary defect in early placentation. The earliest disorder seems to be a "materno-foetal immune maladaptation", characterized by a defective cooperation between uterine NK cells and foetal HLA-C. Defective angiogenesis is also involved, which has been accounted for by an abnormal production of soluble receptors for angiogenic factors and TGF-beta. The resulting placental ischemia is responsible for an increased shedding of trophoblastic debris in the maternal circulation, an inflammatory syndrome, and finally generalized endothelial dysfunction, which is the clue to maternal symptoms. Clinical presentations range from benign isolated hypertension to life-threatening severe preeclampsia, which entails a major risk of maternal complications and foetal death. Antihypertensive treatment does not improve the foetal or maternal prognosis, in spite of blood pressure lowering. Very early preventive treatments have been developed, which seem largely more promising. Research is very active in this field. Finally, women who had preeclampsia are more prone to future hypertension, type 2 diabetes, or coronary disease.

Medications in pregnancy and lactation: Part 2. Drugs with minimal or unknown human teratogenic effect

This is the second of a two-part series on the use of medication during pregnancy and lactation. Pregnancy risk factors together with an increased incidence of chronic diseases and the rise in mean maternal age predict an increase in medication use during gestation. However, as highlighted in the first installment of this series, relatively few medications have specifically been tested for safety and efficacy during pregnancy, and, therefore, responses to those inquiries can be uninformed and inaccurate. Whereas the first installment provided new insight into the nature of medications with known human teratogenic effects, this part concentrates on drugs with minimal or no known human teratogenic effect. It is important that clinicians become familiar with all of the aspects of the drugs they prescribe, in addition to the controversies surrounding them, through consultation with maternal-fetal medicine specialists and through references and Web sites providing up-to-date information in an effort to promote safer prescribing practices.

Vasorelaxant effect of levcromakalim on isolated umbilical arteries of preeclamptic women

OBJECTIVE

Potassium channel openers are revealed to be a new type of antihypertensive drug. We aimed to clarify the effects of levcromakalim, an ATP-sensitive potassium channel opener, on human isolated umbilical artery (UA) and to compare them with those of nifedipine and magnesium sulphate, which are currently used in the treatment of preeclampsia (PE).

STUDY DESIGN

A total of 52 umbilical arteries, isolated immediately after delivery from 27 healthy and 25 preeclamptic pregnant women, were placed into 10-ml organ baths filled with Kreb's solution at physiological pH and temperature. The concentration-dependent relaxations in response to levcromakalim, nifedipine and magnesium sulphate were compared in vessels precontracted with serotonin (1 micromol/l).

RESULTS

The maximal relative relaxation responses (E(max), expressed as percentage of serotonin-induced precontraction) to magnesium sulphate, nifedipine and levcromakalim in umbilical arteries were identical in the healthy (85.06+/-3.31, 84.80+/-3.01 and 80.37+/-5.32%, respectively) and preeclamptic (77.20+/-5.30, 83.36+/-2.37 and 79.13+/-4.30%, respectively) groups.

CONCLUSION

Levcromakalim has a vasodilatory effect on the umbilical artery like magnesium sulphate and nifedipine, and serves as an antihypertensive potential that might be used in the treatment of preeclampsia. However, further experimental and clinical studies are needed to propose that ATP-sensitive potassium channel openers are beneficial drugs in cases of clinical preeclampsia.