Maria Jelinic

Localization of relaxin receptors in arteries and veins, and region-specific increases in compliance and bradykinin-mediated relaxation after in vivo serelaxin treatment

Relaxin is a potent vasodilator of small resistance arteries and modifies arterial compliance in some systemic vascular beds, yet receptors for relaxin, such as RXFP1, have only been localized to vascular smooth muscle. This study first aimed to localize RXFP1 in rat arteries and veins from different organ beds and determine whether receptors are present in endothelial cells. We then tested the hypothesis that region‐specific vascular effects of relaxin may be influenced by the cellular localization of RXFP1 within different blood vessels. The aorta, vena cava, mesenteric artery, and vein had significantly higher (P<0.05) RXFP1 immunostaining in endothelial cells compared with vascular smooth muscle, whereas the femoral artery and vein and small pulmonary arteries had higher (P<0.01) RXFP1 immunostaining in the vascular smooth muscle. Male rats were treated subcutaneously with recombinant human relaxin‐2 (serelaxin; 4 μg/h) for 5 d; vasodilation and compliance in mesenteric and femoral arteries and veins were compared with placebo controls. Serelaxin significantly (P=0.04) reduced wall stiffness and increased volume compliance in mesenteric arteries but not in the other vessels examined. This was associated with changes in geometrical properties, and not compositional changes in the extracellular matrix. Serelaxin treatment had no effect on acetylcholine‐mediated relaxation but significantly (P< 0.001) enhanced bradykinin (BK)‐mediated relaxation in mesenteric arteries, involving enhanced nitric oxide but not endothelium‐derived hyperpolarization or vasodilatory prostanoids. In conclusion, there is differential distribution of RXFP1 on endothelial and smooth muscle across the vasculature. In rats, mesenteric arteries exhibit the greatest functional response to chronic serelaxin treatment.—Jelinic, M., Leo, C‐H., Post Uiterweer, E. P., Sandow, S. L., Gooi, J. H., Wlodek, M. E., Conrad, K. P., Parkington, H., Tare, M., Parry, L. J. Localization of relaxin receptors in arteries and veins, and region‐specific increases in compliance and bradykinin‐mediated relaxation after in vivo serelaxin treatment. FASEB J. 28, 275–287 (2014). www.fasebj.org

Acute Intravenous Injection of Serelaxin (Recombinant Human Relaxin-2) Causes Rapid and Sustained Bradykinin-Mediated Vasorelaxation

Background A recent clinical trial (RELAXin in Acute Heart Failure [RELAX‐AHF]) demonstrated that 48 hours of continuous intravenous infusion of the vasorelaxant peptide serelaxin (recombinant human relaxin‐2) to patients with acute heart failure reduced cardiovascular mortality at 180 days. The persistence of a vasorelaxant response as a potential mechanism for this long‐term benefit and the vascular effects of a bolus intravenous injection of serelaxin have not been examined. This study investigates changes in resistance artery reactivity and passive mechanical wall properties following an intravenous serelaxin injection and whether these vascular effects persist in the absence of detectable circulating serelaxin. Methods and Results Male rats were injected with 13.3 μg/kg serelaxin into the tail vein; mesenteric arteries were assessed 3 and 24 hours after treatment by using wire‐myography. Serelaxin increased basal nitric oxide synthase activity and reduced maximal contraction to endothelin‐1 at 3 hours after administration. Serelaxin treatment also selectively enhanced bradykinin‐mediated endothelium‐dependent relaxation. This effect was sustained for 24 hours in the absence of circulating serelaxin. Serelaxin‐mediated augmentation of bradykinin‐evoked relaxation involved endothelium‐derived hyperpolarization after 3 hours and prostacyclin‐mediated relaxation after 24 hours. Furthermore, upregulation of inducible nitric oxide synthase, phosphorylation of protein kinase B at Ser473 and endothelial nitric oxide synthase at Ser1177 was observed at 24 hours after serelaxin injection. There were no effects of serelaxin on passive arterial wall stiffness. Conclusion Our data show that a bolus intravenous injection of serelaxin modulates endothelial vasodilator function 3 hours after administration, an effect that was sustained for 24 hours. The prolonged bradykinin‐mediated vasorelaxation is principally mediated through prostacyclin.

A Vasoactive Role for Endogenous Relaxin in Mesenteric Arteries of Male Mice

The peptide hormone relaxin has striking effects on the vascular system. Specifically, endogenous relaxin treatment reduces myogenic reactivity through nitric oxide (NO)-mediated vasorelaxation and increases arterial compliance in small resistance arteries. However, less is known about the vascular roles of endogenous relaxin, particularly in males. Therefore, we used male wild-type (Rln +/+) and relaxin knockout (Rln −/−) mice to test the hypothesis that passive wall properties and vascular reactivity in mesenteric arteries would be compromised in Rln −/− mice. Passive compliance was determined in arteries (n = 8–9) mounted on a pressure myograph and in Ca2+-free Krebs containing 2 mM EGTA. Passive volume compliance was significantly (P = 0.01) decreased in the mesenteric arteries of Rln −/− mice. Vascular reactivity was assessed using wire myography. In mesenteric arteries (n = 5) of Rln −/− mice, there was a significant (P<0.03) increase in sensitivity to the vasoconstrictors phenylephrine and thromboxane-mimetic U41669. This enhanced responsiveness to vasoconstrictors was abolished by endothelial denudation, and attributed to impaired NO and prostanoid pathways in Rln −/− mice. Sensitivity to the endothelial agonist acetylcholine was significantly (n = 7–9, P≤0.03) decreased, and this was abolished in the presence of the cyclooxygenase inhibitor, indomethacin (2 µM). This indicates that prostanoid vasoconstrictor pathways were upregulated in the mesenteric arteries of Rln −/− mice. In summary, we demonstrate endothelial dysfunction and impaired arterial wall remodeling in male mice deficient in relaxin. Thus, our results highlight a role for endogenous relaxin in the maintenance of normal mesenteric artery structure and function in males.

Vascular actions of relaxin: nitric oxide and beyond

The peptide hormone relaxin regulates the essential maternal haemodynamic adaptations in early pregnancy through direct actions on the renal and systemic vasculature. These vascular actions of relaxin occur mainly through endothelium‐derived NO‐mediated vasodilator pathways and improvements in arterial compliance in small resistance‐size arteries. This work catalysed a plethora of studies which revealed quite heterogeneous responses across the different regions of the vasculature, and also uncovered NO‐independent mechanisms of relaxin action. In this review, we first describe the role of endogenous relaxin in maintaining normal vascular function, largely referring to work in pregnant and male relaxin‐deficient animals. We then discuss the diversity of mechanisms mediating relaxin action in different vascular beds, including the involvement of prostanoids, VEGF, endothelium‐derived hyperpolarisation and antioxidant activity in addition to the classic NO‐mediated vasodilatory pathway. We conclude the review with current perspectives on the vascular remodelling capabilities of relaxin.

Serelaxin: A Novel Therapeutic for Vascular Diseases

Vascular dysfunction is an important hallmark of cardiovascular disease. It is characterized by increased sensitivity to vasoconstrictors, decreases in the endothelium-derived vasodilators nitric oxide (NO) and prostacyclin (PGI2), and endothelium-derived hyperpolarization (EDH). Serelaxin (recombinant human relaxin) has gained considerable attention as a new vasoactive drug, largely through its beneficial therapeutic effects in acute heart failure. In this review we first describe the contribution of endogenous relaxin to vascular homeostasis. We then provide a comprehensive overview of the novel mechanisms of serelaxin action in blood vessels that differentiate it from other vasodilator drugs and explain how this peptide could be used more widely as a therapeutic to alleviate vascular dysfunction in several cardiovascular diseases.

Enhanced Uterine Artery Stiffness in Aged Pregnant Relaxin Mutant Mice Is Reversed with Exogenous Relaxin Treatment

ABSTRACT Pregnancy is associated with a progressive remodeling of the uterine artery. This adaptation is influenced by local and systemic pregnancy-dependent factors. We recently demonstrated that the peptide hormone relaxin mediates uterine artery remodeling in late pregnant rats. The objective of this study in relaxin gene knockout (Rln−/−) mice was to test the hypothesis that relaxin deficiency throughout pregnancy disrupts uterine artery remodeling, an effect that is exacerbated by aging and reversed with relaxin treatment. Passive mechanical wall properties and extracellular matrix components were measured using pressure myography, quantitative PCR, and zymography in uterine arteries from pregnant wild-type (Rln+/+) and Rln−/− mice aged 5 and 8 mo on Days 12.5 and 17.5 pregnancy. In a second study, 8-mo-old Rln−/− mice received either placebo or human recombinant relaxin subcutaneously for 5 days from Day 12.5 pregnancy. Relaxin deficiency in pregnancy did not alter uterine artery remodeling in young mice. However, remodeling was impaired in older pregnant Rln−/− mice, resulting in significantly stiffer uterine arteries. Uterine arteries of aged Rln−/− pregnant mice had increased expression of elastin, whereas several matrix metalloproteinases and cell adhesion molecules were decreased relative to Rln+/+ mice. Fetal weight was also significantly reduced in Rln−/− mice in late pregnancy in both young and old dams, whereas placental weight was unchanged. Arterial stiffness and reduced fetal weight were reversed after relaxin treatment. In conclusion, relaxin deficiency compromises uterine artery remodeling in older pregnant females, increasing the risk of pregnancy complications such as hypertension and intrauterine growth restriction.

Increased superoxide production and altered nitric oxide-mediated relaxation in the aorta of young but not old male relaxin-deficient mice

The vascular effects of exogenous relaxin (Rln) treatment are well established and include decreased myogenic reactivity and enhanced relaxation responses to vasodilators in small resistance arteries. These vascular responses are reduced in older animals, suggesting that Rln is less effective in mediating arterial function with aging. The present study investigated the role of endogenous Rln in the aorta and the possibility that vascular dysfunction occurs more rapidly with aging in Rln-deficient (Rln(-/-)) mice. We compared vascular function and underlying vasodilatory pathways in the aorta of male wild-type (Rln(+/+)) and Rln(-/-) mice at 4 and 16 mo of age using wire myography. Superoxide production, but not nitrotyrosine or NADPH oxidase expression, was significantly increased in the aorta of young Rln(-/-) mice, whereas endothelial nitric oxide (NO) synthase and basal NO availability were both significantly decreased compared with Rln(+/+) mice. In the presence of the cyclooxygenase inhibitor indomethacin, sensitivity to ACh was significantly decreased in young Rln(-/-) mice, demonstrating altered NO-mediated relaxation that was normalized in the presence of a membrane-permeable SOD or ROS scavenger. These vascular phenotypes were not exacerbated in old Rln(-/-) mice and, in most cases, did not differ significantly from old Rln(+/+) mice. Despite the vascular phenotypes in Rln(-/-) mice, endothelium-dependent and -independent vasodilation were not adversely affected. Our data show a role for endogenous Rln in reducing superoxide production and maintaining NO availability in the aorta but also demonstrate that Rln deficiency does not compromise vascular function in this artery or exacerbate endothelial dysfunction associated with aging.

Time-dependent activation of prostacyclin and nitric oxide pathways during continuous i.v. infusion of serelaxin (recombinant human H2 relaxin)

In the RELAX‐AHF trial, a 48 h i.v. serelaxin infusion reduced systemic vascular resistance in patients with acute heart failure. Consistent with preclinical studies, serelaxin augments endothelial vasodilator function in rat mesenteric arteries. Little is known about the contribution of endothelium‐derived relaxing factors after a longer duration of continuous serelaxin treatment. Here we have assessed vascular reactivity and mechanistic pathways in mesenteric arteries and veins and the aorta after 48 or 72 h continuous i.v. infusion of serelaxin.

Adverse vascular remodelling is more sensitive than endothelial dysfunction to hyperglycaemia in diabetic rat mesenteric arteries.

Increased vascular stiffness and reduced endothelial nitric oxide (NO) bioavailability are characteristic of diabetes. Whether these are evident at a more moderate levels of hyperglycaemia has not been investigated. The objectives of this study were to examine the association between the level of glycaemia and resistance vasculature phenotype, incorporating both arterial stiffness and endothelial function. Diabetes was induced in male Sprague Dawley rats with streptozotocin (STZ; 55mg/kg i.v.) and followed for 8 weeks. One week post STZ, diabetic rats were allocated to either moderate (∼20mM blood glucose, 6-7U/insulins.c. daily) or severe hyperglycaemia (∼30mM blood glucose, 1-2U/insulins.c. daily as required). At study end, rats were anesthetized, and the mesenteric arcade was collected. Passive mechanical wall properties were assessed by pressure myography. Responses to the endothelium-dependent vasodilator acetylcholine (ACh) were assessed using wire myography. Our results demonstrated for the first time that mesenteric arteries from both moderate and severely hyperglycaemic diabetic rats exhibited outward hypertrophic remodelling and increased axial stiffness compared to arteries from non-diabetic rats. Secondly, mesenteric arteries from severely (∼30mM blood glucose), but not moderately hyperglycaemic (∼20mM blood glucose) rats exhibit a significant reduction to ACh sensitivity compared to their non-diabetic counterparts. This endothelial dysfunction was associated with significant reduction in endothelium-derived hyperpolarisation and endothelium-dependent NO-mediated relaxation. Interestingly, endothelium-derived nitroxyl (HNO)-mediated relaxation was intact. Therefore, moderate hyperglycaemia is sufficient to induce adverse structural changes in the mesenteric vasculature, but more severe hyperglycaemia is essential to cause endothelial dysfunction.

Does serelaxin treatment alter passive mechanical wall properties in small resistance arteries

The peptide hormone relaxin is recognized for its connective tissue remodeling actions in the reproductive tract during pregnancy and parturition, but it also has vascular remodeling actions independent of pregnancy. Recombinant human relaxin (serelaxin) treatment in male and non‐pregnant female rodents enhances passive arterial compliance in the renal vasculature. This review focuses on serelaxins actions on passive mechanical wall properties in small arteries and highlights the diversity of responses to serelaxin treatment in rodents. Different experimental approaches (duration of serelaxin treatment, rat strain, age) and animal models of disease (obesity, hypertension) will be considered. Most studies in young rodents demonstrate that serelaxin treatment fails to alter passive compliance in resistance‐size arteries (mesenteric and femoral arteries and cerebral parenchymal arterioles), suggesting that serelaxins beneficial effects are minimal in healthy animals. Short‐term serelaxin treatment (5d) in aged, obese, and spontaneously hypertensive rats (SHRs) is largely without effect on passive mechanical wall properties. However, a longer duration of serelaxin treatment in SHRs (14d) enhances passive compliance in large muscular arteries as well as resistance‐size arteries. In conclusion, serelaxin is capable of vascular remodeling. Its actions are vascular bed‐dependent, more prominent in disease, and likely requires a longer duration of treatment to be effective.