Angiotensin II stimulates the production of NO and peroxynitrite in endothelial cells

Abstract

Angiotensin II (ANG II) produces vasoconstriction by a direct action on smooth muscle cells via AT1 receptors. These receptors are also present in the endothelium, but their function is poorly understood. This study was therefore undertaken to determine whether ANG II elicits the release of nitric oxide (NO) from cultured rat aortic endothelial cells. NO production, measured by the accumulation of nitrite and nitrate, was enhanced by 10−7 M ANG II. The biological activity of the NO released by ANG II action was evaluated by measuring its guanylate cyclase-stimulating activity in smooth muscle cells. The guanosine 3′,5′-cyclic monophosphate (cGMP) content of smooth muscle cells was significantly increased by exposure of supernatant from ANG II-stimulated endothelial cells. These effects resulted from the activation of NO synthase, as they were inhibited by the l-arginine analogs. These ANG II actions were mediated by the AT1 receptor, as shown by their inhibition by the AT1 antagonist losartan. The cGMP production by reporter cells was inhibited by the calmodulin antagonist W-7, suggesting that ANG II activates endothelial calmodulin-dependent NO synthase. This hypothesis is also supported by the increase of intracellular free calcium induced by ANG II in endothelial cells. ANG II also stimulated luminol-enhanced chemiluminescence in endothelial cells. This effect was inhibited by N ω-monomethyl-l-arginine and superoxide dismutase, suggesting that this luminol-enhanced chemiluminescence reflected an increase in peroxynitrite production. Thus ANG II stimulates NO release from macrovascular endothelium, which may modulate the direct vasoconstrictor effect of ANG II on smooth muscle cells. However, this beneficial effect may be counteracted by the simultaneous production of peroxynitrite, which could contribute to several pathological processes in the vascular wall.

Superoxide as a Messenger of Endothelial Function

“…We also found bradykinin causing the same effect and suggest that the generation of PN requires the Ang II or bradykinin receptor pathway for activating NO and • O 2 -production (Pueyo et al, 1998;Shimizu et al, 1994). LPS alone had no major direct influence on the nitration but exerts a priming role for the subsequent receptor-stimulated PN formation.…”

“…It has been demonstrated that Ang II can stimulate • O 2 - (Zhang et al, 1999;Sohn et al, 2000) and NO (Thorup et al, 1998) formation in parallel to generate PN (Pueyo et al, 1998). From fig.…”

Synergistic effect of angiotensin II type 1 receptor and endothelial nitric oxide synthase gene polymorphisms on arterial stiffness

“…7,8 However, it also stimulates the release of endothelium-derived NO with vasodilatory and anti-proliferative properties via same receptor in endothelial cells. 22,23 Thus, the angiotensin II-induced release of NO counterbalances the inverse direct properties of this peptide. The interaction between angiotensin II and eNOS in terms of arterial stiffening demonstrates experimental study by Fitch et al 24 Treatment with angiotensin II or inhibition of eNOS by L-NAME (N-(omega)-nitro-L-arginine methyl ester) did not increase vascular stiffness in mice when administered separately, however, in combination, it did significantly increase PWV (in vivo), maximal passive stiffness (ex vivo) and, moreover, it increased collagen and decreased elastin content in aortic wall.…”

Physiology of the renal medullary microcirculation

“…Of the several sources of O 2 Ϫ ⅐, NADPH oxidase appears to be important. Some NADPH oxidase subunit isoforms are upregulated and activated by vasoconstrictors (36, 57,126,159,165,177). It has been shown that both ANG II receptor blockers (ARBs) and the combination of hydrochlorothiazide, hydralazine, and reserpine (triple therapy) can normalize blood pressure in the SHR rat; however, only ARBs reduce excretion of ROS reaction product 8-iso-PGF 2␣ .…”