Decreased L-arginine-nitric oxide pathway in cultured myoblasts from spontaneously hypertensive versus normotensive Wistar-Kyoto rats

AHU377+Valsartan (LCZ696) Modulates Renin-Angiotensin System (RAS) in the Cardiac of Female Spontaneously Hypertensive Rats Compared With Valsartan

BACKGROUND

Hypertension is a major cause of death and morbidity worldwide and is increasing in prevalence. The Renin-angiotensin system (RAS) is the most common mechanism involved in the pathophysiology of hypertension. Understanding the mechanism of the pathophysiologic processes will help direct potential therapeutic strategies to treat hypertension and improve cardiac function. Recently, a novel drug LCZ696 containing both an angiotensin receptor blocker valsartan and a neprilysin inhibitor (AHU377) has shown a promising effect on the treatment of hypertension. However, the effects of LCZ696 on the expression of main components of RAS, namely, angiotensin-converting enzyme (ACE), angiotensin-converting enzyme 2 (ACE2), angiotensin II type 1 receptor (AT1 R), angiotensin II type 2 receptor (AT2 R), and angiotensin (1-7) receptor/Mas receptor (MasR) remain unclear. The aim of the present study was to evaluate the effects of LCZ696 on the protective arms of RAS in the cardiac tissue when compared with valsartan under the equal inhibition of AT1 R. We hypothesized that the superior effects of LCZ696 may contribute to its greater effect on the RAS than valsartan.

MATERIALS AND METHODS

Sixteen-week-old female spontaneously hypertensive rats (SHRs) were used in this study. Wistar-Kyoto (WKY) rats were used as controls. All rats were randomly divided into LCZ696 (n = 10), valsartan (n = 10), SHR (n = 10), and WKY (n = 10) groups under a 12-hour dark and 12-hour light cycle and provided with regular chow diet and water. The tail-cuff method was performed to measure blood pressure. Cardiac function was assessed by echocardiography.

RESULTS

The blood pressure value was lower in LCZ696 than valsartan in SHR after 12 weeks of treatment. Further, LCZ696 inhibits the ACE and AT1 R protein expression in the cardiac of SHR and significantly upregulate the protective axis of RAS components, including ACE2, MasR, and AT2 R. Left ventricular AT2 R messenger RNA (mRNA) expression was higher in the LCZ696+SHR group compared with valsartan. In addition, real-time polymerase chain reaction analysis revealed that LCZ696 enhanced the mRNA expression of antihypertensive components AT2 R, ACE2, and MasR and decreased the expression of AT1 R. However, only AT2 R and ACE2 mRNA expressions have a statistical difference between the LCZ696 and valsartan groups. No difference was observed in the mRNA expression of ACE and MasR. The stronger positive signal of transforming growth factor β in the left ventricle was inhibited in each administrated group compared with SHR groups.

CONCLUSIONS

LCZ696 ameliorates the vasoconstrictor axis of the RAS AT1 R and stimulate the protective arm effectors, ACE2 and AT2 R, as well as reverses the compensatory upregulation of neuronal nitric oxide synthase and endothelial nitric oxide synthase in SHR. These findings suggest the mechanistic insight of the cardiac-protective and greater hypotensive effects of LCZ696.

Inhibition of overexpression of Giα proteins and nitroxidative stress contribute to sodium nitroprusside-induced attenuation of high blood pressure in SHR

We earlier showed that vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit enhanced expression of Giα proteins which was attributed to the decreased levels of nitric oxide (NO), because elevation of the intracellular levels of NO by NO donors; sodium nitroprusside (SNP) and S-Nitroso-N-acetyl-DL-penicillamine (SNAP), attenuated the enhanced expression of Giα proteins. Since the enhanced expression of Giα proteins is implicated in the pathogenesis of hypertension, the present study was undertaken to investigate if treatment of SHR with SNP could also attenuate the development of high blood pressure (BP) and explore the underlying molecular mechanisms. Intraperitoneal injection of SNP at a concentration of 0.5 mg/kg body weight twice a week for 2 weeks into SHR attenuated the high blood pressure by about 80 mmHg without affecting the BP in WKY rats. SNP treatment also attenuated the enhanced levels of superoxide anion (O₂^- ), hydrogen peroxide (H₂ O₂ ), peroxynitrite (ONOO^- ), and NADPH oxidase activity in VSMC from SHR to control levels. In addition, the overexpression of different subunits of NADPH oxidase; Nox-1, Nox-2, Nox-4, P^22phox , and P^47phox , and Giα proteins in VSMC from SHR were also attenuated by SNP treatment. On the other hand, SNP treatment augmented the decreased levels of intracellular NO, eNOS, and cGMP in VSMC from SHR. These results suggest that SNP treatment attenuates the development of high BP in SHR through the elevation of intracellular levels of cGMP and inhibition of the enhanced levels of Giα proteins and nitroxidative stress.

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.

Natriuretic peptide receptor-C attenuates hypertension in spontaneously hypertensive rats: role of nitroxidative stress and Gi proteins

C-Atrial natriuretic peptide (ANP)4-23, a ring deleted analog of ANP that specifically interacts with natriuretic peptide receptor-C (NPR-C), has been shown to decrease the enhanced expression of Giα proteins implicated in the pathogenesis of hypertension. In the present study, we investigated whether in vivo treatment of spontaneously hypertensive rats (SHRs) with C-ANP4-23 could attenuate the development of high blood pressure (BP) and explored the underlying mechanisms responsible for this response. Intraperitoneal injection of C-ANP4-23 at the concentration of 2 or 10 nmol/kg body weight to prehypertensive SHRs attenuated the development of high BP, and at 8 weeks it was decreased by ≈20 and 50 mm Hg, respectively; however, this treatment did not affect BP in Wistar-Kyoto rats. C-ANP4-23 treatment of adult SHRs for 2 weeks also attenuated high BP, heart rate, and restored the impaired vasorelaxation toward control levels. In addition, the enhanced levels of superoxide anion (O2(-)), peroxynitrite, NADPH oxidase activity, and the enhanced expression of Giα proteins, NOX4, p47(phox), nitrotyrosine, and decreased levels of endothelial nitric oxide synthase (eNOS or NOS3) and NO in SHRs were attenuated by C-ANP4-23 treatment; however, the altered levels of NPR-A/NPR-C were not affected by this treatment. In conclusion, these results indicate that NPR-C activation by C-ANP4-23 attenuates the development of high BP in SHRs through the inhibition of enhanced levels of Giα proteins and nitroxidative stress and not through eNOS/cGMP pathway and suggest that NPR-C ligand may have the potential to be used as therapeutic agent in the treatment of cardiovascular complications including hypertension.

C-type natriuretic peptide effects on cardiovascular nitric oxide system in spontaneously hypertensive rats

The aim was to study the effects of C-type natriuretic peptide (CNP) on mean arterial pressure (MAP) and the cardiovascular nitric oxide (NO) system in spontaneously hypertensive rats (SHR), and to investigate the signaling pathways involved in this interaction. SHR and WKY rats were infused with saline or CNP. MAP and nitrites and nitrates excretion (NO(x)) were determined. Catalytic NO synthase (NOS) activity and endothelial (eNOS), neuronal (nNOS) and inducible NOS (iNOS) were measured in the heart and aorta artery. NOS activity induced by CNP was determined in presence of: iNOS or nNOS inhibitors, NPR-A/B natriuretic peptide receptors blocker and Gi protein and calmodulin inhibitors. CNP diminished MAP and increased NO(x) in both groups. Cardiovascular NOS activity was higher in SHR than in WKY. CNP increased NOS activity, but this activation was lower in SHR. CNP had no effect on NOS isoforms expression. iNOS and nNOS inhibitors did not modify CNP-induced NOS activity. NPR-A/B blockade induced no changes in NOS stimulation via CNP in both tissues. Cardiovascular NOS response to CNP was reduced by Gi protein and calmodulin inhibitors in both groups. CNP interacts with NPR-C receptors, activating Ca-calmodulin eNOS via Gi protein. NOS response to CNP is impaired in the heart and aorta of SHR. Alterations in the interaction between CNP and NO would be involved in the maintenance of high blood pressure in this model of hypertension.

Role of nitric oxide as a key mediator on cardiovascular actions of atrial natriuretic peptide in spontaneously hypertensive rats

The objective was to study atrial natriuretic peptide (ANP) effects on mean arterial pressure (MAP) and cardiovascular nitric oxide (NO) system in spontaneously hypertensive rats (SHRs), investigating the receptors and signaling pathways involved. In vivo, SHRs and Wistar-Kyoto (WKY) rats were infused with saline (0.05 ml/min) or ANP (0.2 μg·kg−1·min−1) for 1 h. MAP and nitrites and nitrates excretion (NOx) were determined. NO synthase (NOS) activity and endothelial (eNOS), neuronal (nNOS) and inducible (iNOS) NOS expression were measured in the heart and aorta. In vitro, heart and aortic NOS activity induced by ANP was determined in the presence of iNOS and nNOS inhibitors, natriuretic peptide receptor (NPR)-A/B blocker, Gi protein, and calmodulin inhibitors. As a result, ANP diminished MAP and increased NOx in both groups. Cardiovascular NOS activity was higher in SHRs than in WKY rats. ANP increased NOS activity, but the activation was lower in SHRs than in WKY rats. ANP had no effect on NOS isoform expression. NOS activity induced by ANP was not modified by iNOS and nNOS inhibitors. NPR-A/B blockade blunted NOS stimulation via ANP in ventricle and aorta but not in atria. Cardiovascular NOS response to ANP was reduced by Gi protein and calmodulin inhibitors in both groups. In conclusion, in atria, ventricle, and aorta, ANP interacts with NPR-C receptors, activating Ca2+-calmodulin eNOS through Gi protein. In ventricle and aorta, NOS activation also involves NPR-A/B. The NOS response to ANP was impaired in heart and aorta of SHRs. The impaired NO-system response to ANP in hypertensive animals, involving alterations in the signaling pathway, could participate in the maintenance of high blood pressure in this model of hypertension.

Association of renal injury with nitric oxide deficiency in aged SHR: prevention by hypertension control with AT1 blockade

BACKGROUND

Aged spontaneously hypertensive rats (SHR) develop end-stage renal disease resembling that of uncontrolled essential hypertension in humans. Nitric oxide (NO) and angiotensin II (Ang II) play an important role in the regulation of blood pressure and the growth of vascular smooth muscle and renal mesangial cells. The relationship between renal NO system, Ang II activity and renal injury in aged SHR is not fully understood.

METHODS

The 8-week-old SHR were randomized into losartan-treated (30 mg/kg/day for 55 weeks) and vehicle treated groups. The age-matched Wistar-Kyoto rats (WKY) served as controls. Renal histology and tissue expressions of endothelial and inducible NO synthases (eNOS and iNOS) and nitrotyrosine were examined at 63-weeks of age.

RESULTS

Compared to the WKY group, untreated SHR showed severe hypertension, proteinuria, renal insufficiency, a twofold decrease in renal tissue eNOS and iNOS expressions and massive nitrotyrosine accumulation. This was associated with severe glomerulosclerosis, tubular atrophy and interstitial fibrosis. Losartan therapy normalized blood pressure, prevented proteinuria and renal insufficiency, abrogated the fall in renal eNOS and iNOS protein contents, mitigated renal nitrotyrosine accumulation, and prevented the histological abnormalities found in the untreated SHR.

CONCLUSIONS

Aged SHR exhibit severe renal lesions with acquired NO deficiency that are prevented by hypertension control with AT1 blockade. These findings point to the possible role of NO deficiency in the pathogenesis of renal lesions in aged SHR.

Docosahexaenoic acid potentiates interleukin-1beta induction of nitric oxide synthase through mechanism involving p44/42 MAPK activation in rat vascular smooth muscle cells

The effect of docosahexaenoic acid (DHA) on nitric oxide (NO) production and inducible NO synthase (iNOS) expression induced by interleukin (IL)-1beta, and whether the effect of DHA is related to its effect on mitogen-activated protein kinase (MAPK) activation were investigated in cultured rat vascular smooth muscle cells (VSMCs). DHA and eicosapentaenoic acid (EPA), although less potent, increased the NO production induced by IL-1beta (3 ng ml(-1)) in a concentration-dependent manner (3 - 30 microM) Arachidonic acid had no significant effect. The stimulatory effect of DHA (30 microM) on the NO production was more obvious at lower concentrations of IL-1beta. IL-1beta induced iNOS protein and mRNA expressions, which were significantly potentiated by DHA. EPA (30 microM) had a tendency to increase the iNOS protein and mRNA expressions, but arachidonic acid had no effect. IL-1beta-induced iNOS protein expression was significantly inhibited by PD 98059 (10 microM), a selective inhibitor of p44/42 MAPK kinase, both in the absence and the presence of DHA. SB 203580 (10 microM), a selective inhibitor of p38 MAPK activity, had no significant effect, although had a tendency to inhibit slightly. IL-1beta increased the phosphorylation of p44/42 MAPK, while it did not apparently increase the phosphorylation of p38 MAPK. DHA significantly potentiated the IL-1beta-induced phosphorylation of p44/42 MAPK, while it had no significant effect on the phosphorylation of p38 MAPK. These results suggest that DHA increases NO production by potentiating iNOS expression induced by IL-1beta through mechanism involving p44/42 MAPK signalling cascade in rat VSMCs. The present study may contribute to the understanding of basic mechanisms underlying the beneficial effects of DHA on various cardiovascular disorders.

Increased activity and expression of Ca(2+)-dependent NOS in renal cortex of ANG II-infused hypertensive rats

We have previously demonstrated that nitric oxide (NO) exerts a greater modulatory influence on renal cortical blood flow in ANG II-infused hypertensive rats compared with normotensive rats. In the present study, we determined nitric oxide synthase (NOS) activities and protein levels in the renal cortex and medulla of normotensive and ANG II-infused hypertensive rats. Enzyme activity was determined by measuring the rate of formation of L-[(14)C]citrulline from L-[(14)C]arginine. Western blot analysis was performed to determine the regional expression of endothelial (eNOS), neuronal (nNOS), and inducible (iNOS) isoforms in the renal cortex and medulla of control and ANG II-infused rats. Male Sprague-Dawley rats were prepared by the infusion of ANG II at a rate of 65 ng/min via osmotic minipumps implanted subcutaneously for 13 days and compared with sham-operated rats. Systolic arterial pressures were 127 +/- 2 and 182 +/- 3 mmHg in control (n = 13) and ANG II-infused rats (n = 13), respectively. The Ca(2+)-dependent NOS activity, expressed as picomoles of citrulline formed per minute per gram wet weight, was higher in the renal cortex of ANG II-infused rats (91 +/- 11) than in control rats (42 +/- 12). Likewise, both eNOS and nNOS were markedly elevated in the renal cortex of the ANG II-treated rats. In both groups of rats, Ca(2+)-dependent NOS activity was higher in the renal medulla than in the cortex; however, no differences in medullary NOS activity were observed between the groups. Also, no differences in medullary eNOS levels were observed between the groups; however, medullary nNOS was decreased by 45% in the ANG II-infused rats. For the Ca(2+)-independent NOS activities, the renal cortex exhibited a greater activity in the control rats (174 +/- 23) than in ANG II-infused rats (101 +/- 10). Similarly, cortical iNOS was greater by 47% in the control rats than in ANG II-treated rats. No differences in the activity were found for the renal medulla between the groups. There was no detectable signal for iNOS in the renal medulla for both groups. These data indicate that there is a differential distribution of NOS activity, with the Ca(2+)-dependent activity and protein expression higher in the renal cortex of ANG II-infused rats compared with control rats, and support the hypothesis that increased constitutive NOS activity exerts a protective effect in ANG II-induced hypertension to maintain adequate renal cortical blood flow.

Upregulation of renal and vascular nitric oxide synthase in young spontaneously hypertensive rats

The available data on the role of the L-arginine/nitric oxide (NO) pathway in the genesis of hypertension in spontaneously hypertensive rats (SHR) are limited and contradictory. In an attempt to address this issue, male SHR were studied during the early phase of evolution of hypertension (age 8 to 12 weeks) to distinguish the primary changes of NO metabolism from those caused by advanced hypertension, vasculopathy, and aging late in the course of the disease. A group of age-matched male Wistar-Kyoto rats (WKY) served as controls. The SHR exhibited a marked rise in arterial blood pressure and a significant increase in urinary excretion and plasma concentration of NO metabolites (nitrite/nitrate [NOx]). Likewise, the SHR showed a significant elevation of thoracic aorta NO synthase (NOS) activity coupled with significant increases of kidney, aorta, inducible NOS (iNOS), and endothelial NOS (eNOS) proteins. In an attempt to determine whether the enhanced L-arginine/NO pathway is a consequence of hypertension, studies were repeated using 3-week-old animals before the onset of hypertension. The study revealed significant increases in urinary NOx excretion as well as vascular eNOS and renal iNOS proteins. In conclusion, the L-arginine/NO pathway is upregulated in young SHR both before and after the onset of hypertension. Thus, development of hypertension is not due to a primary impairment of NO production in SHR. On the contrary, NO production is increased in young SHR both before and after the onset of hypertension.

Investigation of the inhibitory effect of N(G)-nitro-L-arginine methyl ester on the antihypertensive effect of the angiotensin AT1 receptor antagonist, GR138950

1. The effect of systemic administration of the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) on the antihypertensive effects of the angiotensin AT1 receptor antagonist, GR138950, the angiotensin-converting enzyme (ACE) inhibitor, enalapril, or hydralazine has been evaluated in unrestrained, conscious renal artery ligated hypertensive (RALH) rats. The effect of the phosphodiesterase type V inhibitor, zaprinast on the antihypertensive effect of GR138950 in RALH rats was also examined. The effect of GR138950 on blood pressure, and plasma and urine cyclic GMP levels was compared to that of zaprinast in conscious RALH rats. 2. GR138950, enalapril or hydralazine caused marked reductions in blood pressure associated with immediate tachycardia in conscious RALH rats. L-NAME pretreatment attenuated the antihypertensive effects of GR138950 or enalapril but not that of hydralazine in conscious RALH rats. The initial tachycardia caused by GR138950 or enalapril but not hydralazine was attenuated by L-NAME pretreatment. L-NAME alone caused a transient (20 min) pressor response and a prolonged (6 h) bradycardia in conscious RALH rats. 3. Pretreatment with indomethacin did not affect the cardiovascular effect of GR138950 in conscious RALH rats. Indomethacin alone did not significantly change basal blood pressure or heart rate in RALH rats. 4. Zaprinast pretreatment did not affect the antihypertensive effect of GR138950 in conscious RALH rats but potentiated the depressor response to sodium nitroprusside. Zaprinast alone caused a small reduction in basal blood pressure but did not change basal heart rate in RALH rats. 5. The antihypertensive effect of GR138950 was not associated with an increase in plasma or urine cyclic GMP levels in conscious RALH rats, whereas zaprinast caused a small fall in blood pressure associated with increases in plasma and urine cyclic GMP. 6. The ability of L-NAME to inhibit the antihypertensive action of GR138950 or enalapril suggests that these agents release nitric oxide (NO) and/or enhance the cardiovascular effects of NO as part of their mechanism of action. However, the inability of zaprinast to potentiate the antihypertensive effects of GR138950 and the finding that GR138950 did not increase urine and plasma cyclic GMP levels are not consistent with this view. Attenuation of the response to GR138950 or enalapril, but not hydralazine, suggests a selective interaction between L-NAME and inhibitors of the renin-angiotensin system, although the nature of this interaction is unknown.