Relaxin Deficiency Leads to Uterine Artery Dysfunction During Pregnancy in Mice.

The uterine vasculature undergoes profound adaptations in response to pregnancy. Augmentation of endothelial vasodilator function and reduced smooth muscle reactivity are factors contributing to uterine artery adaptation and are critical for adequate placental perfusion. The peptide hormone relaxin has an important role in mediating the normal maternal renal vascular adaptations during pregnancy through a reduction in myogenic tone and an increase in flow-mediated vasodilation. Little is known however about the influence of endogenous relaxin on the uterine artery during pregnancy. We tested the hypothesis that relaxin deficiency increases myogenic tone and impairs endothelial vasodilator function in uterine arteries of late pregnant relaxin deficient (Rln-/-) mice. Reactivity of main uterine arteries from non-pregnant and late pregnant wild-type (Rln+/+) and Rln-/- mice was studied using pressure and wire myography and changes in gene expression explored using PCR. Myogenic tone was indistinguishable in arteries from non-pregnant mice. In late pregnancy uterine artery myogenic tone was halved in Rln+/+ mice (P < 0.0001), an adaptation that failed to occur in arteries from pregnant Rln-/- mice. The role of vasodilator prostanoids in the regulation of myogenic tone was significantly reduced in arteries of pregnant Rln-/- mice (P = 0.02). Agonist-mediated endothelium-dependent vasodilation was significantly impaired in non-pregnant Rln-/- mice. With pregnancy, differences in total endothelial vasodilator function were resolved, although there remained an underlying deficiency in the role of vasodilator prostanoids and alterations to the contributions of calcium-activated K+ channels. Fetuses of late pregnant Rln-/- mice were ~10% lighter (P < 0.001) than those of Rln+/+ mice. In conclusion, relaxin deficiency is associated with failed suppression of uterine artery myogenic tone in pregnancy, which likely contributes to reduced uteroplacental perfusion and fetal growth restriction.

Short-term (48 hours) intravenous serelaxin infusion has no effect on myogenic tone or vascular remodeling in rat mesenteric arteries.

BACKGROUND: Short-term IV sRLX (recombinant human relaxin-2) infusion enhances endothelium-dependent relaxation in mesenteric arteries. This is initially underpinned by increased NO followed by a transition to prostacyclin. The effects of short-term IV sRLX treatment on pressure-induced myogenic tone and vascular remodeling in these arteries are unknown. Therefore, we investigated the effects of sRLX infusion on pressure-induced myogenic tone and passive mechanical wall properties in mesenteric arteries. METHODS: Mesenteric artery myogenic tone and passive mechanics were examined after 48-hours and 10-days infusion of sRLX. Potential mechanisms of action were assessed by pressure myography, qPCR, and Western blot analysis. RESULTS: Neither 48-hours nor 10-days sRLX treatment had significant effects on myogenic tone, passive arterial wall stiffness, volume compliance, or axial lengthening. However, in 48-hours sRLX -treated rats, incubation with the NO synthase blocker L-NAME significantly increased myogenic tone (P<.05 vs placebo), demonstrating an increased contribution of NO to the regulation of myogenic tone. eNOS dimerization, but not phosphorylation, was significantly upregulated in the arteries of sRLX -treated rats. CONCLUSION: In mesenteric arteries, 48-hours sRLX treatment upregulates the role of NO in the regulation of myogenic tone by enhancing eNOS dimerization, without altering overall myogenic tone or vascular remodeling.

Proton Pump Inhibitors Decrease Soluble fms-Like Tyrosine Kinase-1 and Soluble Endoglin Secretion, Decrease Hypertension, and Rescue Endothelial Dysfunction.

Preeclampsia is a severe complication of pregnancy. Antiangiogenic factors soluble fms-like tyrosine kinase-1 (sFlt-1) and soluble endoglin are secreted in excess from the placenta, causing hypertension, endothelial dysfunction, and multiorgan injury. Oxidative stress and vascular inflammation exacerbate the endothelial injury. A drug that can block these pathophysiological steps would be an attractive treatment option. Proton pump inhibitors (PPIs) are safe in pregnancy where they are prescribed for gastric reflux. We performed functional studies on primary human tissues and animal models to examine the effects of PPIs on sFlt-1 and soluble endoglin secretion, vessel dilatation, blood pressure, and endothelial dysfunction. PPIs decreased sFlt-1 and soluble endoglin secretion from trophoblast, placental explants from preeclamptic pregnancies, and endothelial cells. They also mitigated tumor necrosis factor-α-induced endothelial dysfunction: PPIs blocked endothelial vascular cell adhesion molecule-1 expression, leukocyte adhesion to endothelium, and disruption of endothelial tube formation. PPIs decreased endothelin-1 secretion and enhanced endothelial cell migration. Interestingly, the PPI esomeprazole vasodilated maternal blood vessels from normal pregnancies and cases of preterm preeclampsia, but its vasodilatory effects were lost when the vessels were denuded of their endothelium. Esomeprazole decreased blood pressure in a transgenic mouse model where human sFlt-1 was overexpressed in placenta. PPIs upregulated endogenous antioxidant defenses and decreased cytokine secretion from placental tissue and endothelial cells. We have found that PPIs decrease sFlt-1 and soluble endoglin secretion and endothelial dysfunction, dilate blood vessels, decrease blood pressure, and have antioxidant and anti-inflammatory properties. They have therapeutic potential for preeclampsia and other diseases where endothelial dysfunction is involved.

The Role of Relaxin in Normal and Abnormal Uterine Function During the Menstrual Cycle and Early Pregnancy.

The hormone relaxin is a 6-kDa peptide with high structural similarity to insulin. It is primarily produced by the corpus luteum during pregnancy but is also synthesized by other reproductive organs such as the uterus, decidua, and placenta. Relaxin binds to its receptor RXFP1, which has been localized to a wide variety of reproductive and nonreproductive tissues. The peptide's many uterotropic effects include stimulating uterine growth and vascularization, remodeling extracellular matrix components, and regulating vascular endothelial growth factor in preparation for implantation. Evidence also supports a role for relaxin in the systemic maternal vascular adaptations required for a healthy pregnancy. Diminished relaxin levels in early pregnancy are linked with increased risks of miscarriage and the development of preeclampsia. In addition to pregnancy, relaxin may also play a functional role in the uterus during the menstrual cycle, and modified relaxin activity may contribute to gynecological disorders such as uterine fibrosis and endometriosis. Despite over 75 years of research, we still have a limited understanding of relaxin's broad roles in the uterus, particularly as there are significant species differences in its synthesis and activity, which restricts the use of animal models for human-centric questions. Here, we review current knowledge regarding relaxin actions in the human uterus during the menstrual cycle and in early pregnancy, with a focus on its potential roles in various gynecological disorders, as well as the pregnancy disorders such as preeclampsia, recurrent miscarriage, and early pregnancy loss.

Evidence of proteinuria, but no other characteristics of pre-eclampsia, in relaxin-deficient mice.

Pre-eclampsia (PE) is a leading cause of maternal and fetal death, characterised by an imbalance of placental growth factors and hypertension at >20 weeks gestation. Impaired maternal systemic vascular adaptations and fetal growth restriction are features of both PE and pregnant relaxin-deficient (Rln-/-) mice. The aim of the present study was to investigate whether these phenotypes in Rln-/- mice are associated with abnormal placental growth factor expression, increased soluble fms-like tyrosine kinase-1 (sFlt-1), proteinuria and/or hypertension during pregnancy. In addition, we examined relaxin and relaxin receptor (relaxin/insulin like family peptide receptor 1 (RXFP1)) mRNA expression in placentas of women with PE. There was no significant difference in placental vascular endothelial growth factor A (VegfA) and placenta growth factor (Plgf) gene expression between Rln-/- and wild-type mice. Circulating plasma sFlt-1 concentrations in pregnant mice of both genotypes and ages were increased compared with non-pregnant mice but were lower in younger pregnant Rln-/- mice compared with aged-matched Rln+/+ mice. Aged pregnant Rln-/- mice had higher urinary albumin:creatinine ratios compared with age-matched Rln+/+ mice, indicative of proteinuria. Systolic and diastolic blood pressures did not differ between genotypes. In addition, PE in women was not associated with altered placental mRNA expression of RLN2 or RXFP1 at term. Overall, the data demonstrate that pregnant Rln-/- mice do not have the typical characteristics of PE. However, these mice show evidence of proteinuria, but we suggest that this results from systemic renal vascular dysfunction before pregnancy.

Relaxin deficiency attenuates pregnancy-induced adaptation of the mesenteric artery to angiotensin II in mice.

Pregnancy is associated with reduced peripheral vascular resistance, underpinned by changes in endothelial and smooth muscle function. Failure of the maternal vasculature to adapt correctly leads to serious pregnancy complications, such as preeclampsia. The peptide hormone relaxin regulates the maternal renal vasculature during pregnancy; however, little is known about its effects in other vascular beds. This study tested the hypothesis that functional adaptation of the mesenteric and uterine arteries during pregnancy will be compromised in relaxin-deficient (Rln(-/-)) mice. Smooth muscle and endothelial reactivity were examined in small mesenteric and uterine arteries of nonpregnant (estrus) and late-pregnant (day 17.5) wild-type (Rln(+/+)) and Rln(-/-) mice using wire myography. Pregnancy per se was associated with significant reductions in contraction to phenylephrine, endothelin-1, and ANG II in small mesenteric arteries, while sensitivity to endothelin-1 was reduced in uterine arteries of Rln(+/+) mice. The normal pregnancy-associated attenuation of ANG II-mediated vasoconstriction in mesenteric arteries did not occur in Rln(-/-) mice. This adaptive failure was endothelium-independent and did not result from altered expression of ANG II receptors or regulator of G protein signaling 5 (Rgs5) or increases in reactive oxygen species generation. Inhibition of nitric oxide synthase with l-NAME enhanced ANG II-mediated contraction in mesenteric arteries of both genotypes, whereas blockade of prostanoid production with indomethacin only increased ANG II-induced contraction in arteries of pregnant Rln(+/+) mice. In conclusion, relaxin deficiency prevents the normal pregnancy-induced attenuation of ANG II-mediated vasoconstriction in small mesenteric arteries. This is associated with reduced smooth muscle-derived vasodilator prostanoids.