This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Ng HH, Jelinic M, Parry LJ, Leo C. Increased superoxide production and altered nitric oxide-mediated relaxation in the aorta of young but not old male relaxin-deficient mice. Am J Physiol Heart Circ Physiol 309: H285-H296, 2015. First published May 8, 2015 doi:10.1152/ajpheart.00786.2014.-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 Ϫ/Ϫ ) mice. We compared vascular function and underlying vasodilatory pathways in the aorta of male wild-type (Rln ϩ/ϩ ) and Rlnmice 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 Ϫ/Ϫ mice, whereas endothelial nitric oxide (NO) synthase and basal NO availability were both significantly decreased compared with Rln ϩ/ϩ mice. In the presence of the cyclooxygenase inhibitor indomethacin, sensitivity to ACh was significantly decreased in young Rln Ϫ/Ϫ 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 Ϫ/Ϫ mice and, in most cases, did not differ significantly from old Rln ϩ/ϩ mice. Despite the vascular phenotypes in Rln Ϫ/Ϫ 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.

BACKGROUND AND PURPOSEIn 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. EXPERIMENTAL APPROACHMale rats were infused with either placebo or serelaxin (13.3 μg·kg À1 ·h À1 ) via the jugular vein using osmotic minipumps. Vascular function was assessed using wire myography. Changes in gene and protein expression and 6-keto PGF 1α levels were determined by quantitative PCR, Western blot and ELISA respectively. KEY RESULTSContinuous i.v. serelaxin infusion augmented endothelium-dependent relaxation in arteries (mesenteric and aorta) but not in mesenteric veins. In mesenteric arteries, 48 h i.v. serelaxin infusion increased basal NOS activity, associated with increased endothelial NOS (eNOS) expression. Interestingly, phosphorylated-eNOS Ser1177 , eNOS and basal NOS activity were reduced in mesenteric arteries following 72 h serelaxin treatment. At 72 h, serelaxin treatment improved bradykinin-mediated relaxation through COX2-derived PGI 2 production. CONCLUSIONS AND IMPLICATIONSContinuous i.v. serelaxin infusion enhanced endothelial vasodilator function in arteries but not in veins. The underlying mediator at 48 h was NO but there was a transition to PGI 2 by 72 h. Activation of the PGI 2 -dependent pathway is key to the prolonged vascular response to serelaxin treatment. AbbreviationsBK, bradykinin; EDH, endothelium-derived hyperpolarization; eNOS, endothelial NOS; iNOS, inducible NOS; KPSS, K + physiological saline solution; L-NAME, N Ω -nitro-L-arginine methyl ester hydrochloride; pEC 50 , logarithm of the half maximal effective concentration; R max , maximum relaxation; RXFP1, relaxin/insulin-like family peptide receptor 1; SNP, sodium nitroprusside BJP British Journal of Pharmacology

Serelaxin prevents endothelial dysfunction in the mouse aorta ex vivo and inhibits apoptosis in cardiomyocytes under acute hyperglycaemia. Less is known about the effects of serelaxin in an in vivo mouse model of diabetes. Therefore, we tested the hypothesis in streptozotocin (STZ)-treated mice that serelaxin is able to reverse diabetes-induced vascular dysfunction and cardiac remodelling. Mice were divided into citrate buffer + placebo, STZ + placebo and STZ + serelaxin (0.5 mg/kg/d, 2 weeks) groups. After 12 weeks of diabetes, sensitivity to the endothelium-dependent agonist acetylcholine (ACh) was reduced in the mesenteric artery. This was accompanied by an enhanced vasoconstrictor prostanoid contribution and a decrease in endothelium-derived hyperpolarisation (EDH)-mediated relaxation. Serelaxin restored endothelial function by increasing nitric oxide (NO)-mediated relaxation but not EDH. It also normalised the contribution of vasoconstrictor prostanoids to endothelial dysfunction and suppressed diabetes-induced hyper-responsiveness of the mesenteric artery to angiotensin II. Similarly, diabetes reduced ACh-evoked NO-mediated relaxation in the aorta which was reversed by serelaxin. In the left ventricle, diabetes promoted apoptosis, hypertrophy and fibrosis; serelaxin treatment reversed this ventricular apoptosis and hypertrophy, but had no effect on fibrosis. In summary, serelaxin reversed diabetes-induced endothelial dysfunction by enhancing NO-mediated relaxation in the mouse vasculature and attenuating left ventricular hypertrophy and apoptosis.