Nitric oxide synthase induction by ouabain in vascular smooth muscle cells from normotensive and hypertensive rats

Involvement of inducible nitric oxide synthase and estrogen receptor ESR2 (ERβ) in the vascular dysfunction in female type 1 diabetic rats

AIMS

Inflammation is involved in diabetes-related vascular dysfunction. Estrogen receptor ESR2/ERβ induces the expression of inducible nitric oxide (NO) synthase (iNOS) and inflammation. The present study investigated the effect of alloxan-induced type 1 diabetes on the iNOS and ESR2 expression and the effect of the chronic iNOS inhibition on the vascular smooth muscle dysfunction in diabetic female rats. In addition, we evaluated the involvement of ESR2 in iNOS expression.

MAIN METHODS

Alloxan-induced diabetic female rats were treated or not with iNOS inhibitor (L-NIL). iNOS and ESR2 immunostaining, S-nitrosylated proteins and IL-1β protein expression in aorta and plasmatic NO levels were analyzed. Contractile response to noradrenaline was analyzed in endothelium-denuded aorta. iNOS mRNA expression was analyzed in isolated aortic smooth muscle cells (ASMCs) of female rats, incubated with 22 mM glucose and an ESR2 antagonist.

KEY FINDINGS

Aortic iNOS and ESR2 immunostaining, S-nitrosylated proteins, IL-1β protein expression and plasmatic NO levels were all increased, whereas noradrenaline-induced contraction was reduced in aorta of diabetic female rats. With the exception of iNOS and ESR2 immunostaining, all these parameters were corrected by L-NIL treatment. High glucose increased iNOS mRNA expression in ASMCs, which was reduced by an ESR2 antagonist.

SIGNIFICANCE

We demonstrated that increased iNOS-NO contributed to the impairment of the contractile response of aortic smooth muscle cells in female type 1 diabetic rats and that increased expression of iNOS may involve the participation of ESR2/ERβ.

Mesenteric arteries from stroke-prone spontaneously hypertensive rats exhibit an increase in nitric-oxide-dependent vasorelaxation

The endothelium is crucial for the maintenance of vascular tone by releasing several vasoactive substances, including nitric oxide (NO). Systemic mean arterial pressure is primarily regulated by the resistance vasculature, which has been shown to exhibit increased vascular reactivity, and decreased vasorelaxation during hypertension. Here, we aimed to determine the mechanism for mesenteric artery vasorelaxation of the stroke-prone spontaneously hypertensive rat (SHRSP). We hypothesized that endothelial NO synthase (eNOS) is upregulated in SHRSP vessels, increasing NO production to compensate for the endothelial dysfunction. Concentration-response curves to acetylcholine (ACh) were performed in second-order mesenteric arteries; we observed decreased relaxation responses to ACh (maximum effect elicited by the agonist) as compared with Wistar-Kyoto (WKY) controls. Vessels from SHRSP incubated with N^ω-nitro-l-arginine methyl ester and (or) indomethacin exhibited decreased ACh-mediated relaxation, suggesting a primary role for NO-dependent relaxation. Vessels from SHRSP exhibited a significantly decreased relaxation response with inducible NO synthase (iNOS) inhibition, as compared with WKY vessels. Western blot analysis showed increased total phosphorylated NF-κB, and phosphorylated and total eNOS in SHRSP vessels. Overall, these data suggest a compensatory role for NO by increased eNOS activation. Moreover, we believe that iNOS, although increasing NO bioavailability to compensate for decreased relaxation, leads to a cycle of further endothelial dysfunction in SHRSP mesenteric arteries.

Vasorelaxation of goat mesenteric artery is mediated by endothelial Na(+)-K(+)-ATPase

OBJECTIVE

To examine the role of Na(+)-K(+)-ATPase and K(+) channels in mediating vasorelaxation in the superior mesenteric artery of Capra hircus.

MATERIALS AND METHODS

Goat superior mesenteric artery (GSMA) was cut into 1.5-2 mm circular rings and mounted in a thermostatically controlled (37°C ± 0.5°C) organ bath containing 20 ml of modified Krebs-Henseleit saline (MKHS) (pH 7.4), with continuous aeration under 1.5 g tension for 90 min. Endothelium-intact (ED+) or endothelium-denuded (ED-) GSMA ring was contracted with phenylephrine (PE) or 5-hydroxytryptamine (5-HT) (1 μM-0.1 mM) in the absence or presence of ouabain (0.1 μM). KCl (1 μM-10 mM) was added cumulatively to K(+)-free MKHS-pre-contracted (ED+/-) rings in the absence or presence of ouabain (0.1 μM) or barium (1 μM) or 4-aminopyridine (1 μM).

RESULTS

Ouabain did not alter the basal tone of the arterial ring. The contractile response induced by PE (Emax: 50.46 ± 2.68, pD2: 5.53 ± 0.04) and 5-HT (Emax: 30.86 ± 1.33, pD2: 6.17 ± 0.03) in ED+ ring was significantly (P < 0.001) augmented in ED- rings (PE: Emax: 93.30 ± 2.11, pD2: 6.41 ± 0.04; 5-HT: Emax: 95.07 ± 0.99, pD2: 6.27 ± 0.03). The contractile response induced by PE and 5-HT in ED+ or ED- rings in the presence of ouabain was almost identical with that of ED- rings. Vasorelaxation of KCl (Emax: 2.90 ± 1.14, pD2: 3.9 ± 0.03) was significantly attenuated in the presence of ouabain (Emax: 73.8 ± 5.16, pD2: 4.3 ± 0.04), Ba(2+) (Emax: 16.34 ± 4.7, pD2: 3.22 ± 0.02), 4-AP (Emax: 18.16 ± 2.4, pD2: 3.68 ± 0.03), ouabain and Ba(2+) (Emax: 70.09 ± 3.66, pD2: 4.41 ± 0.04), and ouabain and 4-AP (Emax: 66.98 ± 4.61, pD2: 4.13 ± 0.06).

CONCLUSION

The vasorelaxation in GSMA is mediated by the endothelium-derived hyperpolarizing factor (EDHFs) such as ouabain-sensitive Na(+)-K(+)-ATPase, KIR and Kv channels.

Chronic ouabain treatment increases the contribution of nitric oxide to endothelium-dependent relaxation

The aim of this study was to analyze the contribution of nitric oxide, prostacyclin and endothelium-dependent hyperpolarizing factor to endothelium-dependent vasodilation induced by acetylcholine in rat aorta from control and ouabain-induced hypertensive rats. Preincubation with the nitric oxide synthase inhibitor N-omega-nitro-L-arginine methyl esther (L-NAME) inhibited the vasodilator response to acetylcholine in segments from both groups but to a greater extent in segments from ouabain-treated rats. Basal and acetylcholine-induced nitric oxide release were higher in segments from ouabain-treated rats. Preincubation with the prostacyclin synthesis inhibitor tranylcypromine or with the cyclooxygenase inhibitor indomethacin inhibited the vasodilator response to acetylcholine in aortic segments from both groups. The Ca2+-dependent potassium channel blocker charybdotoxin inhibited the vasodilator response to acetylcholine only in segments from control rats. These results indicate that hypertension induced by chronic ouabain treatment is accompanied by increased endothelial nitric oxide participation and impaired endothelium-dependent hyperpolarizing factor contribution in acetylcholine-induced relaxation. These effects might explain the lack of effect of ouabain treatment on acetylcholine responses in rat aorta.

Endogenous and exogenous cardiac glycosides: their roles in hypertension, salt metabolism, and cell growth

Cardiotonic steroids (CTS), long used to treat heart failure, are endogenously produced in mammals. Among them are the hydrophilic cardenolide ouabain and the more hydrophobic cardenolide digoxin, as well as the bufadienolides marinobufagenin and telecinobufagin. The physiological effects of endogenous ouabain on blood pressure and cardiac activity are consistent with the "Na(+)-lag" hypothesis. This hypothesis assumes that, in cardiac and arterial myocytes, a CTS-induced local increase of Na(+) concentration due to inhibition of Na(+)/K(+)-ATPase leads to an increase of intracellular Ca(2+) concentration ([Ca(2+)](i)) via a backward-running Na(+)/Ca(2+) exchanger. The increase in [Ca(2+)](i) then activates muscle contraction. The Na(+)-lag hypothesis may best explain short-term and inotropic actions of CTS. Yet all data on the CTS-induced alteration of gene expression are consistent with another hypothesis, based on the Na(+)/K(+)-ATPase "signalosome," that describes the interaction of cardiac glycosides with the Na(+) pump as machinery activating various signaling pathways via intramembrane and cytosolic protein-protein interactions. These pathways, which may be activated simultaneously or selectively, elevate [Ca(2+)](i), activate Src and the ERK1/2 kinase pathways, and activate phosphoinositide 3-kinase and protein kinase B (Akt), NF-kappaB, and reactive oxygen species. A recent development indicates that new pharmaceuticals with antihypertensive and anticancer activities may be found among CTS and their derivatives: the antihypertensive rostafuroxin suppresses Na(+) resorption and the Src-epidermal growth factor receptor-ERK pathway in kidney tubule cells. It may be the parent compound of a new principle of antihypertensive therapy. Bufalin and oleandrin or the cardenolide analog UNBS-1450 block tumor cell proliferation and induce apoptosis at low concentrations in tumors with constitutive activation of NF-kappaB.

High glucose enhances inducible nitric oxide synthase expression. Role of protein kinase C-betaII

The aim was to determine whether high glucose levels interfere with nitric oxide (NO) production and inducible NO synthase (iNOS) protein expression in interleukin-1beta-stimulated vascular smooth muscle cells from normotensive Wistar Kyoto and spontaneously hypertensive rats. Cells were incubated with either normal (5.5 mM) or high (22 mM) d-glucose for 72 h and with interleukin-1beta (10 ng/ml) for the last 24 h. High glucose increased nitrite levels, iNOS expression and protein kinase C activity in cells from normotensive rats and had no effect in cells from hypertensive rats. High glucose effects on nitrite production and iNOS expression was abolished by the selective inhibitor for the protein kinase C-betaII, 5,21:12,17-dimetheno-18H-dibenzo[i,o]pyrrolo[3,4-1] [1,8]diacyclohexadecine-18,20 (19H)-dione, 8-[(dimethylamino) methyl]-6,7,8,9,10,11-hexahydro-monomethanesulfonate (LY379196, 30 nM). Calphostin C (1 microM) and LY379196 (10 microM) reduced nitrite levels and iNOS expression only in cells from normotensive rats treated with both media. These results suggest that high glucose increases inducible nitric oxide synthase induction and subsequent NO production by activating the protein kinase C-betaII; this mechanism seems to be altered in hypertension.

Vascular effects of the Mangifera indica L. extract (Vimang)

The effects of the Mangiferia indica L. (Vimang) extract, and mangiferin (a C-glucosylxanthone of Vimang) on the inducible isoforms of cyclooxygenase (cyclooxygenase-2) and nitric oxide synthase (iNOS) expression and on vasoconstrictor responses were investigated in vascular smooth muscle cells and mesenteric resistance arteries, respectively, from Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Vimang (0.5-0.1 mg/ml) and mangiferin (0.025 mg/ml) inhibited the interleukin-1beta (1 ng/ml)-induced iNOS expression more in SHR than in WKY, and cyclooxygenase-2 expression more in WKY than in SHR. Vimang (0.25-1 mg/ml) reduced noradrenaline (0.1-30 microM)- and U46619 (1 nM-30 microM)- but not KCl (15-70 mM)-induced contractions. Mangiferin (0.05 mg/ml) did not affect noradrenaline-induced contraction. In conclusion, the antiinflammatory action of Vimang would be related with the inhibition of iNOS and cyclooxygenase-2 expression, but not with its effect on vasoconstrictor responses. Alterations in the regulation of both enzymes in hypertension would explain the differences observed in the Vimang effect.

Nanomolar level of ouabain increases intracellular calcium to produce nitric oxide in rat aortic endothelial cells

Changes in [Ca(2+)](i) across the cell membrane and/or the sarcoplasmic reticulum regulate endothelial nitric oxide (NO) synthase activity. In the present study, we investigated the effect of ouabain, a specific inhibitor of Na(+)/K(+)-ATPase, on NO release and [Ca(2+)](i) movements in cultured rat aortic endothelial cells (RAEC) by monitoring NO production continuously using an NO-specific real-time sensor and by measuring the change in [Ca(2+)](i) using a fluorescence microscopic imaging technique with high-speed wavelength switching. The t((1/2)) (half-time of the decline of [Ca(2+)](i) to basal levels after stimulation with 10 micro mol/L bradykinin) was used as an index of [Ca(2+)](i) extrusion. A very low concentration of ouabain (10 nmol/L) did not increase the peak of NO production, but decreased the decay of NO release and, accordingly, increased integral NO production by the maximal dose-response concentration induced by bradykinin. The same dose of ouabain affected [Ca(2+)](i) movements across the cell membrane and/or sarcoplasmic reticulum induced by bradykinin with a time-course similar to that of NO release. Moreover, the t((1/2)) was significantly increased. Pretreatment of RAEC with Na(+)-free solution, an inhibitor of the Na(+)/Ca(2+) exchanger, and nickel chloride hexahydrate prevented the effects induced by bradykinin and ouabain. These observations using real-time recording indicate that a small amount of ouabain contributes to the bradykinin-stimulated increase of NO production through inhibition of plasma membrane Na(+)/K(+)-ATPase activity and an increase in intracellular Na(+) concentrations. The membrane was then depolarized, leading to a decline in the bradykinin-stimulated increase in [Ca(2+)](i) by forward mode Na(+)/Ca(2+) exchange to prolong the Ca(2+) signal time. From these results, we suggest that nanomolar levels of ouabain modulate [Ca(2+)](i) movements and NO production in RAEC.

Ouabain changes arterial blood pressure and vascular reactivity to phenylephrine in L-NAME-induced hypertension

Ouabain is an endogenous compound that has been associated with the genesis and maintenance of hypertension. This compound inhibits the Na+ pump activity, which leads to an accumulation of intracellular Na and ultimately might increase vascular tone. In nanomolar concentrations, it enhances vasopressor responses to phenylephrine in some vascular beds from normotensive and hypertensive rats. However, it is not known whether this action of ouabain is a common mechanism for all models of hypertension. The aim of this work was to determine whether ouabain can alter pressor responses to phenylephrine in rats with Nomega-nitro-l-arginine methyl ester (L-NAME)-induced hypertension. In anesthetized rats, ouabain (0.18 microg/kg, i.v.) increased arterial blood pressure in L-NAME-treated rats but not in controls. Ganglionic blockade by hexamethonium (5 mg/kg, i.v.) prevented the increase in arterial blood pressure produced by ouabain in L-NAME-treated rats. Additional studies using isolated perfused tail artery preparations were performed to investigate which factors are involved in the action of ouabain in L-NAME-treated rats. The effects of 10 nM ouabain on the vasoconstrictor actions of phenylephrine were determined on preparations with intact or damaged endothelium or in the presence of tetraethylammonium (a K+-channel blocker). Ouabain reduced pressor actions of phenylephrine in preparations with an intact endothelium. However, after endothelial damage or infusing tetraethylammonium, the response to phenylephrine was increased after ouabain. In tails from L-NAME-treated rats, the functional activity of the Na, K+-ATPase was reduced, and 10 nM ouabain did not produce any further reduction. In conclusion, in this model of hypertension, a low dose of ouabain (0.18 microg/kg) increased arterial blood pressure in vivo probably as a result of increased sympathetic tone. However, this effect was not accompanied by an enhanced action of phenylephrine on the tail vascular bed with an intact endothelium. The results suggest that this was due to the release of an endothelium-derived K+-channel opener.

Ouabain-induced hypertension is accompanied by increases in endothelial vasodilator factors

The involvement of nitric oxide (NO), prostaglandins, and calcium-dependent potassium channel (K(Ca)) activators on the negative modulation of phenylephrine-induced contractions was evaluated on the isolated aorta and caudal (CAU) artery obtained from rats treated with ouabain for 5 wk to induce hypertension. In ouabain-treated rats, the reactivity to phenylephrine was reduced in the endothelium-intact aorta but not the CAU segments. Endothelial modulation of phenylephrine contraction, as demonstrated by endothelium removal, NO synthase (NOS) inhibition with N(omega)-nitro-L-arginine methyl ester and aminoguanidine, as well as K(Ca) inhibition with tetraethylammonium, was more pronounced in segments from ouabain-treated animals, and here greater effects were seen in the aorta than in CAU. An increased expression of endothelial NOS and neuronal NOS was seen in the aorta after ouabain treatment. In CAU, only endothelial NOS was detected and ouabain treatment did not alter its expression. These results suggest that ouabain-induced hypertension is accompanied by increased NO release derived from endothelial NOS and neuronal NOS and increased release of an endothelial hyperpolarizing factor that presumably opens K(Ca), all of which contribute to the increased negative modulation of the phenylephrine contraction.

A novel inhibitor of inducible nitric oxide synthase (ONO-1714) prevents critical warm ischemia-reperfusion injury in the pig liver

BACKGROUND

Recently, a novel inhibitor of inducible nitric oxide synthase, ONO-1714, was developed. We evaluated the effect of ONO-1714 on a critical warm I/R model of the pig liver.

METHODS

Pigs were subjected to 180 min of hepatic warm I/R under the extracorporeal circulation. We investigated the time course of changes in the serum NO2- + NO3- (NOx), the cellular distribution of endothelial and inducible nitric oxide synthase, thrombocyte-thrombi, and nitrotyrosine by immunohistochemistry. The hepatic tissue blood flow (HTBF) was measured continuously using a laser-Doppler blood flowmeter.

RESULTS

ONO-1714 at 0.05 mg/kg improved the survival rate from 54 (control group) to 100%. The serum NOx levels in the ONO-1714 group were significantly lower than those in the control group at 1, 1.5, 2, 3, and 6 hr after reperfusion. The serum aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels of the ONO-1714 group were significantly lower than the control group, and the HTBF of the ONO-1714 group was significantly higher than the control group. The formation of thrombocyte-thrombi and nitrotyrosine after reperfusion was significantly lower in the ONO-1714 group.

CONCLUSIONS

These results indicated that ONO-1714 improved the survival rates and attenuated I/R injury in a critical hepatic warm I/R model of the pig. ONO-1714 will be beneficial for hepatectomy or liver transplantation in the clinical field.

Reciprocal regulation of endothelin-1 and nitric oxide: relevance in the physiology and pathology of the cardiovascular system

The endothelium plays a crucial role in the regulation of cardiovascular structure and function by releasing several mediators in response to biochemical and physical stimuli. These mediators are grouped into two classes: (1) endothelium-derived constricting factors (EDCFs) and (2) endothelium-derived relaxing factors (EDRFs), the roles of which are considered to be detrimental and beneficial, respectively. Endothelin-1 (ET-1) and nitric oxide (NO) are the prototypes of EDCFs and EDRFs, respectively, and their effects on the cardiovascular system have been studied in depth. Numerous conditions characterized by an impaired availability of NO have been found to be associated with enhanced synthesis of ET-1, and vice versa, thereby suggesting that these two factors have a reciprocal regulation. Experimental studies have provided evidence that ET-1 may exert a bidirectional effect by either enhancing NO production via ETB receptors located in endothelial cells or blunting it via ETA receptors prevalently located in the vascular smooth muscle cells. Conversely, NO was found to inhibit ET-1 synthesis in different cell types. In vitro and in vivo studies have started to unravel the molecular mechanisms involved in this complex interaction. It has been clarified that several factors affect in opposite directions the transcription of preproET-1 and NO-synthase genes, nuclear factor-KB and peroxisome proliferator-activated receptors playing a key role in these regulatory mechanisms. ET-1 and NO interplay seems to have a great relevance in the physiological regulation of vascular tone and blood pressure, as well as in vascular remodeling. Moreover, an imbalance between ET-1 and NO systems may underly the mechanisms involved in the pathogenesis of systemic and pulmonary hypertension and atherosclerosis.

Alterations in phenylephrine-induced contractions and the vascular expression of Na+,K+-ATPase in ouabain-induced hypertension

Hypertension development, phenylephrine-induced contraction and Na(+),K(+)-ATPase functional activity and protein expression in aorta (AO), tail (TA) and superior mesenteric (SMA) arteries from ouabain- (25 microg day(-1), s.c., 5 weeks) and vehicle-treated rats were evaluated. Ouabain treatment increased systolic blood pressure (127+/-1 vs 160+/-2 mmHg, n=24, 35; P<0.001) while the maximum response to phenylephrine was reduced (P<0.01) in AO (102.8+/-3.9 vs 67.1+/-10.1% of KCl response, n=12, 9) and SMA (82.5+/-7.5 vs 52.2+/-5.8%, n=12, 9). Endothelium removal potentiated the phenylephrine response to a greater extent in segments from ouabain-treated rats. Thus, differences of area under the concentration-response curves (dAUC) in endothelium-denuded and intact segments for control and ouabain-treated rats were, respectively: AO, 56.6+/-9.6 vs 198.3+/-18.3 (n=9, 7); SMA, 85.5+/-15.4 vs 165.4+/-24.8 (n=6, 6); TA, 13.0+/-6.1 vs 39.5+/-10.4% of the corresponding control AUC (n=6, 6); P<0.05. The relaxation to KCl (1 - 10 mM) was similar in segments from both groups. Compared to controls, the inhibition of 0.1 mM ouabain on KCl relaxation was greater in AO (dAUC: 64.8+/-4.6 vs 84.0+/-5.1%, n=11, 14; P<0.05), similar in SMA (dAUC: 39.1+/-3.9 vs 43.3+/-7.8%, n=6, 7; P>0.05) and smaller in TA (dAUC: 62.1+/-5.5 vs 41.4+/-8.2%, n=12, 13; P<0.05) in ouabain-treated rats. Protein expression of both alpha(1) and alpha(2) isoforms of Na(+),K(+)-ATPase was augmented in AO, unmodified in SMA and reduced in TA from ouabain-treated rats. These results suggest that chronic administration of ouabain induces hypertension and regional vascular alterations, the latter possibly as a consequence of the hypertension.