α ₂ -Adrenoceptors Enhance Angiotensin II–Induced Renal Vasoconstriction

Abstract

Abstract-␣ 2 -Adrenoceptors potentiate renal vascular responses to angiotensin II via coincident signaling at phospholipase C. This leads to increased activation of the phospholipase C/protein kinase C/c-src pathway. Studies suggest that c-src activates the reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase/superoxide system, and reactive oxygen species stimulate the RhoA/Rho kinase pathway. Therefore, we hypothesized that NADPH oxidase/superoxide and RhoA/Rho kinase are downstream components of the signal transduction pathway that mediate the interaction between ␣ 2 -adrenoceptors and angiotensin II on renal vascular resistance. In rat kidneys, both in vivo and in vitro, intrarenal infusions of angiotensin II increased renal vascular resistance, and UK14,304 (␣ 2 -adrenoceptor agonist) enhanced this response. Intrarenal Tempol (superoxide dismutase mimetic) or Y27632 (Rho kinase inhibitor) abolished the interaction between UK14,304 and angiotensin II both in vivo and in vitro. The interaction was also blocked by inhibitors of NADPH oxidase (in vivo using chronic gp91ds-tat administration and in vitro with diphenyleneiodonium).In cultured preglomerular vascular smooth muscle cells, UK14,304 enhanced angiotensin II-induced intracellular superoxide (2-hydroxyethidium production) and potentiated activation of RhoA (Western blot of activated RhoA bound to the binding domain of rhotekin). The interaction between angiotensin II and UK14,304 on superoxide generation and RhoA activation was blocked by inhibitors of phospholipase C (U73312), protein kinase C (GF109203X), c-src (PP1), NADPH oxidase (diphenyleneiodonium), or superoxide (Tempol). We conclude that NADPH oxidase/superoxide and RhoA/Rho kinase are involved in the interaction between ␣ 2 -adrenoceptors and angiotensin II on renal vascular resistance by mediating signaling events downstream of the phospholipase C/protein kinase C/c-src pathway. Key Words: phospholipase C Ⅲ protein kinase C Ⅲ c-src Ⅲ NADPH oxidase Ⅲ superoxide Ⅲ RhoA Ⅲ Rho kinase R enal ␣ 2 -adrenoceptors enhance angiotensin (Ang) IIinduced increases in renal vascular resistance (RVR), particularly in animals with genetic hypertension. 1,2 Previous studies suggest that the signal transduction pathway mediating ␣ 2 -adrenoceptor-induced enhancement of Ang II-induced renal vasoconstriction involves coincident signaling (convergence of signaling) at the level of phospholipase C (PLC), followed by activation of protein kinase C (PKC). The evidence for this conclusion is that U73122 (PLC inhibitor) and GF109203X (PKC inhibitor) abrogate ␣ 2 -adrenoceptorinduced enhancement of Ang II-induced renal vasoconstriction. 2,3 Moreover, activation of G i by ␣ 2 -adrenoceptors releases ␤␥ subunits, 4 and stimulation of Ang II type 1 receptors releases ␣ q from Gq. 5 As reviewed by Selbie and Hill, 6 ␤␥ subunits released by Gi-coupled receptors can synergize with ␣ q subunits released by Gq-coupled receptors to a cause a more robust activation of PLC (most likely PLC-␤ isoforms) and its downstre...

Reactive Oxygen Species Are Involved in Regulating Hypocontractility of Mesenteric Artery to Norepinephrine in Cirrhotic Rats with Portal Hypertension

“…Losartan or apocynin reduces ROS content and ameliorates the low responses of blood vessel to vasoconstrictor in the mesenteric artery in rats induced by bile duct ligation 10. Recent studies have reported that ROS can affect the function of ROCK in vascular smooth muscles in vascular diseases such as pulmonary hypertension 11, hypertension 12,13 and cerebrovascular disease 14. Therefore, we speculate that ROS may be participated in the regulation of ROCK in vascular smooth muscle.…”

Cigarette Smoke Impairs Clearance of Apoptotic Cells through Oxidant-dependent Activation of RhoA

“…The effect of CS on the RhoA-Rho kinase pathway also appears to be systemic, because CS exposure activates Rho kinase in the forearm vasculature of human subjects, leading to a higher degree of vasoreactivity (71). More broadly, reactive oxidant species activate the RhoA-Rho kinase pathway in several settings, both in an NADPH oxidasedependent and -independent manner (34,69,(72)(73)(74); but the converse has also been observed, that reactive oxygen species may down-regulate RhoA activity (75). So reactive oxygen species may retain the ability to activate or deactivate Rho GTPases, depending on the context.…”

Endogenous adenosine contributes to renal sympathetic neurotransmission via postjunctional A1receptor-mediated coincident signaling

“…First, basal perfusion pressures are lower than arterial pressure because the kidneys are perfused with Tyrode's solution, which has much lower viscosity compared with blood (2). Despite this, the isolated, perfused rat kidney is characterized by high vascular sensitivity to vasoconstrictors (17,36,51) and the vascular response of the preparation is similar to that observed in vivo (34). Second, Tyrode's solution is a poor oxygen carrier.…”