Endothelial dysfunction in atherosclerotic mice: improved relaxation by combined supplementation with L‐arginine‐tetrahydrobiopterin and enhanced vasoconstriction by endothelin

Abstract

1 Mice lacking the apolipoprotein E and low density lipoprotein receptor genes (E8xLDLR8) 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 E8xLDLR8 mice. 2 Histological examination revealed severe atherosclerosis of the thoracic aorta of E8xLDLR8 mice. Relaxations induced by acetylcholine (Ach), but not that to sodium nitroprusside, were signi®cantly impaired in E8xLDLR8 mice compared to control mice indicating attenuated endothelium-dependent relaxations. 3 Preincubation with the nitric oxide (NO) substrate L-arginine did not a ect, whereas the cofactor 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 E8xLDLR8 mice. The relaxations induced by Ach in E8xLDLR8 mice in the presence of L-arginine and BH 4 were not di erent from those observed in control mice. 4 Preincubation with superoxide dismutase did not a ect Ach-induced relaxations in aorta from E8xLDLR8 mice. 5 The contractile response to ET-1 was enhanced in E8xLDLR8 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 E8xLDLR8 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 E8xLDLR8 mice.

Cardioprotective effect of an endothelin receptor antagonist during ischaemia/reperfusion in the severely atherosclerotic mouse heart

“…This appears to be in contrast to previous reports demonstrating impaired endothelium-dependent vasorelaxation and reduced concentration of NO derived from the aorta of the atherosclerotic mouse (Barton et al, 1998;Jiang et al, 2000;Scalia et al, 2001). However, in the isolated whole heart preparation, it cannot be determined whether the released NO X is derived from the coronary vessels or the myocardium.…”

“…It is therefore of pathophysiological and therapeutic importance to elucidate whether ET receptor antagonism protects the myocardium in a situation of severe atherosclerosis with endothelial dysfunction, as is the situation in patients with acute myocardial infarction. The apolipoprotein E/LDL receptor-deficient mouse is an atherosclerotic mouse model characterised by endothelial dysfunction due to impaired response to the endothelium-dependent vasodilatator acetylcholine and increased expression of ET-1 and ET receptors (Barton et al, 1998;Jiang et al, 2000;Kobayashi et al, 2000;d'Uscio et al, 2002). Therefore, this model is useful to investigate whether cardioprotection is achieved under severely atherosclerotic conditions.…”

“…This was investigated in knockout (KO) mice lacking the gene encoding apolipoprotein E and low-density lipoprotein (LDL) receptor and fed a cholesterol-rich diet. It has previously been demonstrated that this model develops an atherosclerosis that resembles human atherosclerotic lesions and endothelial dysfunction (Plump et al, 1992;Zhang et al, 1992;Nakashima et al, 1994;Jiang et al, 2000).…”

“…NO not only counteracts the vasoconstrictor effect of ET-1 (Kourembanas et al, 1991) but also inhibits the production and release of ET-1 from endothelial cells (Boulanger & Lu¨scher, 1990). In atherosclerotic arteries, the production of ET is enhanced and the vasoconstrictor response to exogenous ET-1 is more pronounced (Jiang et al, 2000). Pharmacological blockade of ET receptors results in improved endothelium-dependent vasodilatation in atherosclerotic mice (Barton et al, 1998) and in patients with atherosclerosis (Bohm et al, 2002b).…”

Sarcoplasmic-endoplasmic reticulum Ca2+-ATPase inhibition prevents endothelin A receptor antagonism in rat aorta

“…Later, growing evidence suggested that caveolin-1 regulates the interaction of ET-1 with its receptors (37). Moreover, increased vascular reactivity to ET-1 in hypercholesterolemic animals and human subjects supports the role of caveolar localization of ET A , especially in pathophysiological conditions (14,24). Most recently, caveolin-1-deficient aortic smooth muscle cells show abnormal ET-mediated signal transduction (10).…”