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

The role of smooth muscle endothelinB (ETB) 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 ETB receptors would reduce BP, alter vascular contractility, and inhibit neointimal remodeling. ETB receptors were selectively deleted from smooth muscle by crossing floxed ETB mice with those expressing cre-recombinase controlled by the transgelin promoter. Functional consequences of ETB 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 ETB was confirmed by genotyping, autoradiography, polymerase chain reaction, and immunohistochemistry. ETB-mediated contraction was reduced in trachea, but abolished from mesenteric veins, of knockout mice. Induction of ETB-mediated contraction in mesenteric arteries was also abolished in these mice. Femoral artery function was unaltered, and baseline BP modestly elevated in smooth muscle ETB knockout compared with controls (+4.2±0.2 mm Hg; P<0.0001), but salt-induced and ETB blockade-mediated hypertension were unaltered. Circulating endothelin-1 was not altered in knockout mice. ETB-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 ETB knockout mice. In the absence of other pathology, ETB receptors in vascular smooth muscle make a small but significant contribution to ETB-dependent regulation of BP. These ETB receptors have no effect on vascular contraction or neointimal remodeling.

Selective endothelin A receptor antagonism with sitaxentan reduces neointimal lesion size in a mouse model of intraluminal injury.

BACKGROUND AND PURPOSE: Endothelin (ET) receptor antagonism reduces neointimal lesion formation in animal models. This investigation addressed the hypothesis that the selective ETA receptor antagonist sitaxentan would be more effective than mixed ETA / B receptor antagonism at inhibiting neointimal proliferation in a mouse model of intraluminal injury. EXPERIMENTAL APPROACH: Antagonism of ETA receptors by sitaxentan (1-100 nM) was assessed in femoral arteries isolated from adult, male C57Bl6 mice using isometric wire myography. Neointimal lesion development was induced by intraluminal injury in mice receiving sitaxentan (ETA antagonist; 15 mg·kg(-1) ·day(-1) ), A192621 (ETB antagonist; 30 mg·kg(-1) ·day(-1) ), the combination of both antagonists or vehicle. Treatment began 1 week before, and continued for 28 days after, surgery. Femoral arteries were then harvested for analysis of lesion size and composition. KEY RESULTS: Sitaxentan produced a selective, concentration-dependent parallel rightward shift of ET-1-mediated contraction in isolated femoral arteries. Sitaxentan reduced neointimal lesion size, whereas ETB and combined ETA / B receptor antagonism did not. Macrophage and α-smooth muscle actin content were unaltered by ET receptor antagonism but sitaxentan reduced the amount of collagen in lesions. CONCLUSIONS AND IMPLICATIONS: These results suggest that ETA receptor antagonism would be more effective than combined ETA /ETB receptor antagonism at reducing neointimal lesion formation.

Non-endothelial cell endothelin-B receptors limit neointima formation following vascular injury.

AIMS: The potent vasoconstrictor endothelin-1 (ET-1), acting on the endothelin-A (ETA) receptor, promotes intimal lesion formation following vascular injury. The endothelin-B (ETB) receptor, which mediates nitric oxide release and ET-1 clearance in endothelial cells, may moderate lesion formation, but this is less clear. We used selective ET receptor antagonists and cell-specific deletion to address the hypothesis that ETB receptors in the endothelium inhibit lesion formation following arterial injury. METHODS AND RESULTS: Neointimal proliferation was induced by wire or ligation injury to the femoral artery in mice treated with selective ETA (ABT-627) and/or ETB antagonists (A192621). Measurement of lesion formation by optical projection tomography and histology indicated that ETA blockade reduced lesion burden in both models. Although ETB blockade had little effect on ligation injury-induced lesion formation, after wire injury, blockade of the ETB receptor increased lesion burden (184% of vehicle; P < 0.05) and reversed the protective effects of an ETA antagonist. Selective deletion of ETB receptors from the endothelium, however, had no effect on neointimal lesion size. CONCLUSION: These results are consistent with ETB receptor activation playing an important role in limiting neointimal lesion formation following acute vascular injury, but indicate that this protective effect is not mediated by those ETB receptors expressed by endothelial cells. These data support the proposal that selective ETA antagonists may be preferable to mixed ETA/ETB antagonists for targeting the arterial response to injury.