Abstract
1. Mice lacking the apolipoprotein E and low density lipoprotein receptor genes (E degrees xLDLR degrees ) develop atherosclerosis and endothelial dysfunction. The aim of this study was to characterize the roles of L-arginine and tetrahydrobiopterin (BH(4)) for endothelium-dependent relaxation and the changes in the vasoconstrictor response to endothelin-1 (ET-1) in thoracic aortic rings of E degrees xLDLR degrees mice. 2. Histological examination revealed severe atherosclerosis of the thoracic aorta of E degrees xLDLR degrees mice. Relaxations induced by acetylcholine (Ach), but not that to sodium nitroprusside, were significantly impaired in E degrees xLDLR degrees mice compared to control mice indicating attenuated endothelium-dependent relaxations. 3. Preincubation with the nitric oxide (NO) substrate L-arginine did not affect, whereas the co-factor for NO synthase, BH(4), slightly improved the relaxations induced by Ach. Combined preincubation with L-arginine and BH(4) induced a pronounced enhancement of Ach-induced relaxations in E degrees xLDLR degrees mice. The relaxations induced by Ach in E degrees xLDLR degrees mice in the presence of L-arginine and BH(4) were not different from those observed in control mice. 4. Preincubation with superoxide dismutase did not affect Ach-induced relaxations in aorta from E degrees xLDLR degrees mice. 5. The contractile response to ET-1 was enhanced in E degrees xLDLR degrees mouse aorta. The contractions were abolished by the ET(A) receptor antagonist LU 135252. The ET(B) receptor agonist sarafotoxin 6c did not induce contractions or relaxations. 6. It is concluded that endothelial dysfunction of E degrees xLDLR degrees mouse aorta is reversed by combined administration of L-arginine and BH(4). In addition, the ET(A) receptor-mediated vasoconstriction by ET-1 is enhanced in E degrees xLDLR degrees mice.