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

Abstract

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.

Serelaxin treatment reverses vascular dysfunction and left ventricular hypertrophy in a mouse model of Type 1 diabetes

“…Vascular function was assessed as previously described2122 with the following modifications. Briefly, first order mesenteric arteries and abdominal aortae were cut into two mm long rings and mounted on a multi-wire myograph system 620 M (Danish Myo Technology, Aarhus, Denmark) and allowed to stabilise at zero tension for 15 min followed by normalisation.…”

“…Snap frozen LV were homogenised in ice cold lysis buffer as previously described21. Protein concentration of each sample was quantified using a BCA protein assay kit (ThermoScientific).…”

“…Total RNA was extracted from frozen LV using TRI Reagent solution (Ambion, Mulgrave, VIC, Australia) as described previously2122, resulting in A260/280 values > 1.90. All RNA samples were DNAase treated using DNA- free TM DNA removal kit (Ambion, Mulgrave, VIC, Australia) following manufacturer’s protocol to eliminate genomic DNA.…”

“…It mediates its actions through its major receptor, relaxin/insulin-like family peptide receptor 1 (RXFP1), which is localised in the endothelial and vascular smooth muscle cells in both arteries and veins2021. Relaxin infusion for 48 hours increases bradykinin (BK)-evoked NO-mediated relaxation, basal NO synthase (NOS) activity and endothelial NOS (eNOS) protein expression, as well as increases both NO and COX-2 derived PGI 2 -mediated relaxation at 72 hours post infusion in healthy rat mesenteric arteries22.…”

Extravascular Blood Augments Myogenic Constriction of Cerebral Arterioles: Implications for Hemorrhage‐Induced Vasospasm

“…We demonstrated previously that increases in smooth muscle Ca 2+ level contribute significantly to the basilar cerebral artery constriction in response to hemolyzed blood 19. To date, the specific mechanism responsible for superoxide‐dependent altered myogenic constriction is proposed primarily as impaired NO bioavailability, as a function of superoxide scavenge of NO 20, 21. In the present study, however, enhanced myogenic constriction behaved in an endothelium‐independent manner that was reversible with Tempel (Figure 6), suggesting that the effects of superoxide on arteriolar myogenic constriction are not predominantly caused by its scavenging of NO22 or simply independent of NO 23.…”