Smooth Muscle Endothelin B Receptors Regulate Blood Pressure but Not Vascular Function or Neointimal Remodeling.

The role of smooth muscle endothelin(B) (ET(B)) receptors in regulating vascular function, blood pressure (BP), and neointimal remodeling has not been established. Selective knockout mice were generated to address the hypothesis that loss of smooth muscle ET(B) receptors would reduce BP, alter vascular contractility, and inhibit neointimal remodeling. ET(B) receptors were selectively deleted from smooth muscle by crossing floxed ET(B) mice with those expressing cre-recombinase controlled by the transgelin promoter. Functional consequences of ET(B) deletion were assessed using myography. BP was measured by telemetry, and neointimal lesion formation induced by femoral artery injury. Lesion size and composition (day 28) were analyzed using optical projection tomography, histology, and immunohistochemistry. Selective deletion of ET(B) was confirmed by genotyping, autoradiography, polymerase chain reaction, and immunohistochemistry. ET(B)-mediated contraction was reduced in trachea, but abolished from mesenteric veins, of knockout mice. Induction of ET(B)-mediated contraction in mesenteric arteries was also abolished in these mice. Femoral artery function was unaltered, and baseline BP modestly elevated in smooth muscle ET(B) knockout compared with controls (+4.2±0.2 mm Hg; P<0.0001), but salt-induced and ET(B) blockade-mediated hypertension were unaltered. Circulating endothelin-1 was not altered in knockout mice. ET(B)-mediated contraction was not induced in femoral arteries by incubation in culture medium or lesion formation, and lesion size was not altered in smooth muscle ET(B) knockout mice. In the absence of other pathology, ET(B) receptors in vascular smooth muscle make a small but significant contribution to ET(B)-dependent regulation of BP. These ET(B) receptors have no effect on vascular contraction or neointimal remodeling.