Endothelin-1 induces contraction of female rat internal pudendal and clitoral arteries through ETA receptor and rho-kinase activation

Introduction.: Endothelin-1 (ET-1), a potent vasoconstrictor peptide, acts mainly through the Gprotein-coupled ET_A receptor (ET_AR). Increased vascular ET-1 production and constrictor sensitivity have been observed in various cardiovascular diseases, including hypertension, as well as erectile dysfunction. The internal pudendal artery (IPA) supplies blood to the vagina and clitoris. Inadequate blood flow through the IPA may lead to insufficient vaginal engorgement and clitoral tumescence. Aim.: Characterize the effects of ET-1 on the IPA and clitoral artery (CA). Methods.: IPA and CA from female Sprague Dawley rats (225-250 g) were mounted in myograph chambers. Arterial segments were submitted to increasing concentrations of ET-1 (10-10-10-6 M). Segments were incubated with the ET_AR antagonist, atrasentan (10-8 M) or the Rho-kinase inhibitor, Y-27632 (10-6 M) 30 minutes prior to agonist exposure. All E_max values are expressed as % KCl-induced maximal contraction. ET_AR, RhoA, and Rho-kinase expression from IPA was evaluated by Western blot. mRNA of preproET-1, ET_AR, ET_BR, RhoA, and Rho-kinase were measured by real time PCR. Main Outcome Measures.: ET-1 constrictor sensitivity in IPA and CA, protein expression and messenger RNA levels of ET-1-mediated constriction components. Results.: ET-1 concentration-dependently contracted IPA (% Contraction and pD2, respectively: 156 ± 18, 8.2 ± 0.1) and CA (163 ± 12, 8.8 ± 0.08), while ET_AR antagonism reduced ET-1-mediated contraction (IPA: 104 ± 23, 6.4 ± 0.2; CA: 112 ± 17, 6.6 ± 0.08). Pretreatment with Y-27632 significantly shifted ET-1 pD2 in IPA (108 ± 24, 7.9 ± 0.1) and CA (147 ± 58 and 8.0 ± 0.25). Protein expression of ET_AR, ET_BR, RhoA, and Rho-kinase were detected in IPA. IPA and CA contained preproET-1, ET_AR, ET_BR, RhoA, and Rho-kinase message. Conclusion.: We observed that the IPA and CA are sensitive to ET-1, signaling through the ET_AR and Rho-kinase pathway. These data indicate that ET-1 may play a role in vaginal and clitoral blood flow and may be important in pathologies where ET-1 levels are elevated.