Short-term ANG II produces renal vasoconstriction independent of TP receptor activation and TxA2/isoprostane production

Reactivity of renal and mesenteric resistance vessels to angiotensin II is mediated by NOXA1/NOX1 and superoxide signaling

Activation of NADPH oxidase (NOX) enzymes and the generation of reactive oxygen species and oxidative stress regulate vascular and renal function and contribute to the pathogenesis of hypertension. The present study examined the role of NOXA1/NOX1 function in vascular reactivity of renal and mesenteric resistance arteries/arterioles of wild-type and Noxa1-/- mice. A major finding was that renal blood flow is less sensitive to acute stimulation by angiotensin II (ANG II) in Noxa1-/- mice compared with wild-type mice, with a direct action on resistance arterioles independent of nitric oxide (NO) bioavailability. These functional results were reinforced by immunofluorescence evidence of NOXA1/NOX1 protein presence in renal arteries, afferent arterioles, and glomeruli as well as their upregulation by ANG II. In contrast, the renal vascular response to the thromboxane mimetic U46619 was effectively blunted by NO and was similar in both mouse genotypes and thus independent of NOXA1/NOX1 signaling. However, phenylephrine- and ANG II-induced contraction of isolated mesenteric arteries was less pronounced and buffering of vasoconstriction after acetylcholine and nitroprusside stimulation was reduced in Noxa1-/- mice, suggesting endothelial NO-dependent mechanisms. An involvement of NOXA1/NOX1/O2•- signaling in response to ANG II was demonstrated with the specific NOXA1/NOX1 assembly inhibitor C25 and the nonspecific NOX inhibitor diphenyleneiodonium chloride in cultured vascular smooth muscle cells and isolated mesenteric resistance arteries. Collectively, our data indicate that the NOX1/NOXA1/O2•- pathway contributes to acute vasoconstriction induced by ANG II in renal and mesenteric vascular beds and may contribute to ANG II-induced hypertension.NEW & NOTEWORTHY Renal reactivity to angiotensin II (ANG II) is mediated by superoxide signaling produced by NADPH oxidase (NOX)A1/NOX1. Acute vasoconstriction of renal arteries by ANG was blunted in Noxa1-/- compared with wild-type mice. NOXA1/NOX1/O2•- signaling was also observed in ANG II stimulation of vascular smooth muscle cells and isolated mesenteric resistance arteries, indicating that it contributes to ANG II-induced hypertension. A NOXA1/NOX1 assembly inhibitor (C25) has been characterized that inhibits superoxide production and ameliorates the effects of ANG II.

Renal vasoconstriction by vasopressin V1a receptors is modulated by nitric oxide, prostanoids, and superoxide but not the ADP ribosyl cyclase CD38

Renal blood flow (RBF) responses to arginine vasopressin (AVP) were tested in anesthetized wild-type (WT) and CD38(-/-) mice that lack the major calcium-mobilizing second messenger cyclic ADP ribose. AVP (3-25 ng) injected intravenously produced dose-dependent decreases in RBF, reaching a maximum of 25 ± 2% below basal RBF in WT and 27 ± 2% in CD38(-/-) mice with 25 ng of AVP. Renal vascular resistance (RVR) increased 75 ± 6% and 78 ± 6% in WT and CD38(-/-) mice. Inhibition of nitric oxide (NO) synthase with nitro-L-arginine methyl ester (L-NAME) increased the maximum RVR response to AVP to 308 ± 76% in WT and 388 ± 81% in CD38(-/-) (P < 0.001 for both). Cyclooxygenase inhibition with indomethacin increased the maximum RVR response to 125 ± 15% in WT and 120 ± 14% in CD38(-/-) mice (P < 0.001, <0.05). Superoxide suppression with tempol inhibited the maximum RVR response to AVP by 38% in both strains (P < 0.005) but was ineffective when administered after L-NAME. The rate of RBF recovery (relaxation) after AVP was slowed by L-NAME and indomethacin (P < 0.001, <0.005) but was unchanged by tempol. All vascular responses to AVP were abolished by an AVP V1a receptor antagonist. A V2 receptor agonist or antagonist had no effect on AVP-induced renal vasoconstriction. Taken together, the results indicate that renal vasoconstriction by AVP in the mouse is strongly buffered by vasodilatory actions of NO and prostanoids. The vasoconstriction depends on V1a receptor activation without involvement of CD38 or concomitant vasodilatation by V2 receptors. The role of superoxide is to enhance the contractile response to AVP, most likely by reducing the availability of NO rather than directly stimulating intracellular contraction signaling pathways.

Pharmacological evidence showing significant roles for potassium channels and CYP epoxygenase metabolites in the relaxant effects of docosahexaenoic acid on the rat aorta contracted with U46619

Docosahexaenoic acid (DHA) shows more pronounced relaxation when blood vessel is contracted with prostanoid receptor agonists than other stimulants. The present study was carried out to obtain information on the mechanisms underlying prostanoid receptor-selective relaxant action of DHA, particularly focusing on the possible roles for K(+) channels and its CYP epoxygenase (EOX) metabolites. In endothelium-denuded rat thoracic aorta, DHA (10(-5) M) almost completely relaxed U46619 (a thromboxane A2 (TP) receptor agonist)-contracted muscle without substantially affecting noradrenaline (NA)-induced contraction. DHA-induced relaxation was not affected by a large conductance, calcium- and voltage-activated K(+) (BK) channels inhibitor iberiotoxin (IbTX, 10(-7) M) but was almost abolished by high-KCl (8×10(-2) M) or 10(-2) M tetraethylammonium (TEA) which non-selectively inhibits K(+) channel activity. DHA also prominently relaxed U46619-contracted aorta even in the presence of CYP inhibitors (SKF525A or miconazole, each at 10(-5) M). However, in the presence of these CYP inhibitors, the relaxant action of DHA was not affected by 10(-2) M TEA. In supporting a significant role for CYP EOX metabolites in the blood vessel relaxation to DHA, 16,17-epoxy docosapentaenoic acid (16,17-EpDPE), but not 19,20-EpDPE, showed a potent relaxation in U46619-contracted aorta, and this action was significantly attenuated by 10(-2) M TEA. The present findings suggest that the relaxant action of DHA shown in the rat aorta contracted through the stimulation with TP receptor is generated by DHA itself and its CYP EOX metabolites. The relaxant effect of DHA metabolites seems to be partly triggered by the activation of K(+) channels though the role for BK channel is insignificant.

Thromboxane-induced renal vasoconstriction is mediated by the ADP-ribosyl cyclase CD38 and superoxide anion

The present renal hemodynamic study tested the hypothesis that CD38 and superoxide anion (O2(·-)) participate in the vasoconstriction produced by activation of thromboxane prostanoid (TP) receptors in the mouse kidney. CD38 is the major mammalian ADP-ribosyl cyclase contributing to vasomotor tone through the generation of cADP-ribose, a second messenger that activates ryanodine receptors to release Ca(2+) from the sarcoplasmic reticulum in vascular smooth muscle cells. We evaluated whether the stable thromboxane mimetic U-46619 causes less pronounced renal vasoconstriction in CD38-deficient mice and the involvement of O2(·-) in U-46619-induced renal vasoconstriction. Our results indicate that U-46619 activation of TP receptors causes renal vasoconstriction in part by activating cADP-ribose signaling in renal resistance arterioles. Based on maximal renal blood flow and renal vascular resistance responses to bolus injections of U-46619, CD38 contributes 30-40% of the TP receptor-induced vasoconstriction. We also found that the antioxidant SOD mimetic tempol attenuated the magnitude of vasoconstriction by U-46619 in both groups of mice, suggesting mediation by O2(·-). The degree of tempol blockage of U-46619-induced renal vasoconstriction was greater in wild-type mice, attenuating renal vasoconstriction by 40% compared with 30% in CD38-null mice. In other experiments, U-46619 rapidly stimulated O2(·-) production (dihydroethidium fluorescence) in isolated mouse afferent arterioles, an effect abolished by tempol. These observations provide the first in vivo demonstration of CD38 and O2(·-) involvement in the vasoconstrictor effects of TP receptor activation in the kidney and in vitro evidence for TP receptor stimulation of O2(·-) production by the afferent arteriole.

Selective and potent inhibitory effect of docosahexaenoic acid (DHA) on U46619-induced contraction in rat aorta

Inhibitory effects of docosahexaenoic acid (DHA) on blood vessel contractions induced by various constrictor stimulants were investigated in the rat thoracic aorta. The inhibitory effects of DHA were also compared with those of eicosapentaenoic acid (EPA) and linoleic acid (LA). DHA exhibited a strong inhibitory effect on the sustained contractions induced by U46619, a TXA(2) mimetic. This inhibitory effect of DHA was not affected by removal of the endothelium or by treatment with either indomethacin or N(ω)-nitro-l-arginine. DHA also significantly diminished PGF(2α)-induced contraction but did not show any appreciable inhibitory effects on the contractions to both phenylephrine (PE) and high-KCl. Similarly, EPA exhibited significant inhibitory effects against the contractions induced by both U46619 and PGF(2α) without substantially affecting either PE- or high-KCl-induced contractions. However, both DHA and EPA generated more potent inhibitions against contractions induced by U46619 than those by PGF(2α). In contrast, LA did not show significant inhibitory effects against any contractions, including those induced by U46619. The present findings suggest that DHA and EPA elicit more selective inhibition against blood vessel contractions that are mediated through stimulation of prostanoid receptors than those through α-adrenoceptor stimulation or membrane depolarization. Although DHA and EPA have similar inhibitory potencies against prostanoid receptor-mediated contractions, they had a more potent inhibition against TXA(2) receptor (TP receptor)-mediated contractions than against PGF(2α) receptor (FP receptor)-mediated responses. Selective inhibition by either DHA or EPA of prostanoid receptor-mediated blood vessel contractions may partly underlie the mechanisms by which these ω-3 polyunsaturated fatty acids exert their circulatory-protective effects.

Developmental effect of antenatal exposure to betamethasone on renal angiotensin II activity in the young adult sheep

Antenatal corticosteroids may have long-term effects on renal development which have not been clearly defined. Our objective was to compare the responses to intrarenal infusions of ANG II in two groups of year-old, male sheep: one group exposed to a clinically relevant dose of betamethasone before birth and one not exposed. We wished to test the hypothesis that antenatal steroid exposure would enhance renal responses to ANG II in adult life. Six pairs of male sheep underwent unilateral nephrectomy and renal artery catheter placement. The sheep were infused for 24 h with ANG II or with ANG II accompanied by blockade of the angiotensin type 1 (AT(1)) or type 2 (AT(2)) receptor. Baseline mean arterial blood pressure among betamethasone-exposed sheep was higher than in control animals (85.8 +/- 2.2 and 78.3 +/- 1.0 mmHg, respectively, P = 0.003). Intrarenal infusion of ANG II did not increase systemic blood pressure (P >/= 0.05) but significantly decreased effective renal plasma flow and increased renal artery resistance (P < 0.05). The decrease in flow and increase in resistance were significantly greater in betamethasone- compared with vehicle-exposed sheep (betamethasone P < 0.05, vehicle P >/= 0.05). This effect appeared to be mediated by a heightened sensitivity to the AT(1) receptor among betamethasone-exposed sheep. Sodium excretion initially decreased in both groups during ANG II infusion; however, a rebound was observed after 24 h. AT(1) blockade was followed by a significant rebound after 24 h in both groups. AT(2) blockade blunted the 24-h rebound effect among the vehicle-exposed sheep compared with the betamethasone-exposed sheep. In conclusion, antenatal corticosteroid exposure appears to modify renal responsiveness to ANG II by increasing AT(1)- and decreasing AT(2) receptor-mediated actions particularly as related to renal blood flow and sodium excretion.

Cellular mediators of renal vascular dysfunction in hypertension

The renal vasculature plays a major role in the regulation of renal blood flow and the ability of the kidney to control the plasma volume and blood pressure. Renal vascular dysfunction is associated with renal vasoconstriction, decreased renal blood flow, and consequent increase in plasma volume and has been demonstrated in several forms of hypertension (HTN), including genetic and salt-sensitive HTN. Several predisposing factors and cellular mediators have been implicated, but the relationship between their actions on the renal vasculature and the consequent effects on renal tubular function in the setting of HTN is not clearly defined. Gene mutations/defects in an ion channel, a membrane ion transporter, and/or a regulatory enzyme in the nephron and renal vasculature may be a primary cause of renal vascular dysfunction. Environmental risk factors, such as high dietary salt intake, vascular inflammation, and oxidative stress further promote renal vascular dysfunction. Renal endothelial cell dysfunction is manifested as a decrease in the release of vasodilatory mediators, such as nitric oxide, prostacyclin, and hyperpolarizing factors, and/or an increase in vasoconstrictive mediators, such as endothelin, angiotensin II, and thromboxane A(2). Also, an increase in the amount/activity of intracellular Ca(2+) concentration, protein kinase C, Rho kinase, and mitogen-activated protein kinase in vascular smooth muscle promotes renal vasoconstriction. Matrix metalloproteinases and their inhibitors could also modify the composition of the extracellular matrix and lead to renal vascular remodeling. Synergistic interactions between the genetic and environmental risk factors on the cellular mediators of renal vascular dysfunction cause persistent renal vasoconstriction, increased renal vascular resistance, and decreased renal blood flow, and, consequently, lead to a disturbance in the renal control mechanisms of water and electrolyte balance, increased plasma volume, and HTN. Targeting the underlying genetic defects, environmental risk factors, and the aberrant renal vascular mediators involved should provide complementary strategies in the management of HTN.