The role of nitric oxide in angiotensin II-induced renal vasoconstriction in renovascular hypertension

The role of nitric oxide in renovascular hypertension: from the pathophysiology to the treatment

Renovascular hypertension is one of the most relevant causes of secondary hypertension, mostly caused by atherosclerotic renovascular stenosis or fibromuscular dysplasia. The increase in angiotensin II production, oxidative stress, and formation of peroxynitrite promotes the decrease in nitric oxide (NO) availability and the development of hypertension, renal and endothelial dysfunction, and cardiac and vascular remodeling. The NO produced by nitric oxide synthases (NOS) acts as a vasodilator; however, endothelial NOS uncoupling (eNOS) also contributes to NO reduced availability in renovascular hypertension. NO donors and NO-derived metabolites have been investigated in experimental renovascular hypertension and have shown promissory effects in attenuating blood pressure and organ damage in this condition. Therefore, understanding the role of decreased NO in the pathophysiology of renovascular hypertension promotes the study and development of NO donors and molecules that can be converted into NO (such as nitrate and nitrite), contributing for the treatment of this condition in the future.

Developmental programming of cardiovascular function: a translational perspective

The developmental origins of health and disease (DOHaD) is a concept linking pre- and early postnatal exposures to environmental influences with long-term health outcomes and susceptibility to disease. It has provided a new perspective on the etiology and evolution of chronic disease risk, and as such is a classic example of a paradigm shift. What first emerged as the 'fetal origins of disease', the evolution of the DOHaD conceptual framework is a storied one in which preclinical studies played an important role. With its potential clinical applications of DOHaD, there is increasing desire to leverage this growing body of preclinical work to improve health outcomes in populations all over the world. In this review, we provide a perspective on the values and limitations of preclinical research, and the challenges that impede its translation. The review focuses largely on the developmental programming of cardiovascular function and begins with a brief discussion on the emergence of the 'Barker hypothesis', and its subsequent evolution into the more-encompassing DOHaD framework. We then discuss some fundamental pathophysiological processes by which developmental programming may occur, and attempt to define these as 'instigator' and 'effector' mechanisms, according to their role in early adversity. We conclude with a brief discussion of some notable challenges that hinder the translation of this preclinical work.

Rosiglitazone, a Ligand to PPARγ, Improves Blood Pressure and Vascular Function through Renin-Angiotensin System Regulation

Rosiglitazone (RGZ), a peroxisome proliferator-activated receptor gamma (PPARγ) ligand, has been reported to act as insulin sensitizer and exert cardiovascular actions. In this work, we hypothesized that RGZ exerts a PPARγ–dependent regulation of blood pressure through modulation of angiotensin-converting enzyme (ACE)-type 2 (ACE2)/angiotensin-(1-7)/angiotensin II type-2 receptor (AT₂R) axis in an experimental model of high blood pressure. We carried on experiments in normotensive (Sham) and aortic coarctation (AoCo)-induced hypertensive male Wistar rats. Both sham and AoCo rats were treated 7 days with vehicle (V), RGZ (5 mg/kg/day), or RGZ+BADGE (120 mg/kg/day) post-coarctation. We measured blood pressure and vascular reactivity on aortic rings, as well as the expression of renin-angiotensin system (RAS) proteins. We found that RGZ treatment in AoCo group decreases blood pressure values and improves vascular response to acetylcholine, both parameters dependent on PPARγ-stimulation. RGZ lowered serum angiotensin II (AngII) but increased Ang-(1-7) levels. It also decreased 8-hydroxy-2′-deoxyguanosine (8-OH-2dG), malondialdehyde (MDA), and improved the antioxidant capacity. Regarding protein expression of RAS, RGZ decreases ACE and angiotensin II type 1 receptor (AT₁R) and improved ACE2, AT₂R, and Mas receptor in AoCo rats. Additionally, an in silico analysis revealed that 5′UTR regions of RAS and PPARγ share motifs with a transcriptional regulatory role. We conclude that RGZ lowers blood pressure values by increasing the expression of RAS axis proteins ACE2 and AT₂R, decreasing the levels of AngII and increasing levels of Ang-(1-7) in a PPARγ-dependent manner. The in silico analysis is a valuable tool to predict the interaction between PPARγ and RAS.

Role of Nitric Oxide in the Cardiovascular and Renal Systems

The gasotransmitters are a family of gaseous signaling molecules which are produced endogenously and act at specific receptors to play imperative roles in physiologic and pathophysiologic processes. As a well-known gasotransmitter along with hydrogen sulfide and carbon monoxide, nitric oxide (NO) has earned repute as a potent vasodilator also known as endothelium-derived vasorelaxant factor (EDRF). NO has been studied in greater detail, from its synthesis and mechanism of action to its physiologic, pathologic, and pharmacologic roles in different disease states. Different animal models have been applied to investigate the beneficial effects of NO as an antihypertensive, renoprotective, and antihypertrophic agent. NO and its interaction with different systems like the renin–angiotensin system, sympathetic nervous system, and other gaseous transmitters like hydrogen sulfide are also well studied. However, links that appear to exist between the endocannabinoid (EC) and NO systems remain to be fully explored. Experimental approaches using modulators of its synthesis including substrate, donors, and inhibitors of the synthesis of NO will be useful for establishing the relationship between the NO and EC systems in the cardiovascular and renal systems. Being a potent vasodilator, NO may be unique among therapeutic options for management of hypertension and resulting renal disease and left ventricular hypertrophy. Inclusion of NO modulators in clinical practice may be useful not only as curatives for particular diseases but also for arresting disease prognoses through its interactions with other systems.

Peroxisome proliferator-activated receptors (PPAR) downregulate the expression of pro-inflammatory molecules in an experimental model of myocardial infarction

Myocardial infarction (MI) has been associated with an inflammatory response and a rise in TNF-α, interleukin (IL)-1β, and IL-6. Peroxisome proliferator-activated receptors (PPARs) promote a decreased expression of inflammatory molecules. We aimed to study whether PPAR stimulation by clofibrate decreases inflammation and reduces infarct size in rats with MI. Male Wistar rats were randomized into 3 groups: control, MI + vehicle, and MI + clofibrate (100 mg/kg). Treatment was administered for 3 consecutive days, previous to 2 h of MI. MI induced an increase in protein expression, mRNA content, and enzymatic activity of inducible nitric oxide synthase (iNOS). Additionally, MI incited an increased expression of matrix metalloproteinase (MMP)-2 and MMP-9, intercellular adhesion molecule (ICAM)-1, and IL-6. MI also elevated the nuclear content of nuclear factor-κB (NF-κB) and decreased IκB, both in myocyte nuclei and cytosol. Clofibrate treatment prevented MI-induced changes in iNOS, MMP-2 and MMP-9, ICAM-1, IL-6, NF-κB, and IκB. Infarct size was smaller in clofibrate-treated rats compared to MI-vehicle animals. In silico analysis exhibited 3 motifs shared by genes from renin-angiotensin system, PPARα, iNOS, MMP-2 and MMP-9, ICAM-1, and VCAM-1, suggesting a cross regulation. In conclusion, PPARα-stimulation prevents overexpression of pro-inflammatory molecules and preserves viability in an experimental model of acute MI.

Insulin increases the functional activity of the renal NaCl cotransporter

OBJECTIVES

Insulin is recognized to increase renal salt reabsorption in the distal nephron and hyperinsulinemic states have been shown to be associated with increased expression of the renal NaCl cotransporter (NCC). However, the effect of insulin on NCC functional activity has not been reported.

METHODS

Using a heterologous expression system of Xenopus laevis oocytes, a mouse distal convoluted cell line, mDCT15 cells, endogenously expressing NCC, and an ex-vivo kidney perfusion technique, we assessed the effect of insulin on the activity and phosphorylation of NCC. The signaling pathway involved was analyzed.

RESULTS

In Xenopus oocytes insulin increases the activity of NCC together with its phosphorylation at threonine residue 58. Activation of NCC by insulin was also observed in mDCT15 cells. Additionally, insulin increased the NCC phosphorylation in kidney under the ex-vivo perfusion technique. In oocytes and mDCT15 cells, insulin effect on NCC was prevented with inhibitors of phosphatidylinositol 3-kinase (PI3K), mTORC2, and AKT1 kinases, but not by inhibitors of MAP or mTORC1 kinases, suggesting that PI3K-mTORC2-AKT1 is the intracellular pathway required. Additionally, activation of NCC by insulin was not affected by wild-type or mutant versions of with no lysine kinase 1, with no lysine kinase 4, or serum glucocorticoid kinase 1, but it was no longer observed in the presence of wild-type or the dominant negative, catalytically inactive with no lysine kinase 3, implicating this kinase in the process.

CONCLUSION

Insulin induces activation and phosphorylation of NCC. This effect could play an important role in arterial hypertension associated with hyperinsulinemic states, such as obesity, metabolic syndrome, or type 2 diabetes mellitus.

Clofibrate PPARα activation reduces oxidative stress and improves ultrastructure and ventricular hemodynamics in no-flow myocardial ischemia

Peroxisome proliferator-activated receptors (PPAR) play a critical physiological role in energy homeostasis, in inflammation, and a protective role in cardiovascular function. We assessed the antioxidant effect of clofibrate-induced Peroxisome proliferator-activated receptor alpha (PPARα) stimulation on ischemic myocardium on myocardial morphology and hemodynamics. Male Wistar rats (300 g) were distributed into the following groups: (1) Sham, (2) myocardial ischemia vehicle treated (MI-V), and (3) myocardial ischemia clofibrate [100 mg/kg/ intraperitoneally) treated (MI-C). Reactive oxygen species (ROS) and lipid peroxidation increased in MI-V, whereas clofibrate prevented this effect. Superoxide dismutase (SOD)-1 and SOD-2 expression increased 4 times upon PPARα stimulation. SOD-1, SOD-2, and catalase activity also increased in response to clofibrate. eNOS mRNA and tetrahydrobiopterin increased in the MI-C group. Clofibrate was able to decrease Angiotensin II (AngII), AngII AT1-receptor, whereas Ang-(1-7) and AngII AT2-receptor expression increased. Assessment of myocardial morphology and cardiac function show that clofibrate improved histological features and hemodynamic parameters. Our results suggest that PPARα stimulation by clofibrate increases the antioxidant defense, leading to improved cardiac function.

In-vivo evidence of a role for nitric oxide in regulating the activity of the norepinephrine transporter

We examined the role of nitric oxide (NO) in the regulation of neuronal uptake of norepinephrine (uptake-1) in rats under anesthesia. The effect on systolic blood pressure of two pressor drugs that work by different mechanisms, norepinephrine and angiotensin II, was explored in anesthetized rats under control conditions and after prevention of NO synthesis with Nw-nitro-L-arginine (L-NNA). The results showed that whereas the pressor effects of increasing doses of norepinephrine were potentiated by L-NNA, those of angiotensin II were not affected, which implied that NO was selectively involved in modulating the pressor effect of norepinephrine. To explore the mechanisms involved in this potentiation, we examined the effect of L-NNA on the pressor effect of tyramine, a purely-indirectly-acting sympathomimetic amine which enters nerve terminals thorough uptake 1 and liberates norepinephrine from storage vesicles. Increasing doses of tyramine produced pressor effects which, in contrast to those of norepinephrine, were significantly attenuated by pre-treatment with L-NNA. Similarly, pretreatment with cocaine, the classical inhibitor of uptake 1, significantly decreased the pressor effect of tyramine; however, the response to tyramine was then restored when L-NNA was administered, thus reversing the effect of cocaine. We conclude that NO plays a major role in the adrenergic system by enhancing the activity of uptake 1 in sympathetic nerve terminals. Blockade of uptake 1 by cocaine is also partly dependent on NO. The stimulus for the mobilization of the NO synthase pathway in adrenergic neurons and the subsequent steps involved in modulating uptake 1 deserve further exploration.

Effect of clofibrate on vascular reactivity in a model of high blood pressure secondary to aortic coarctation

The aims of this study were to identify the effect of clofibrate administration in the development of high blood pressure secondary to aortic coarctation (AoCo) and to assess its effect on vascular reactivity. Three experimental groups of rats were used: sham-operated, aortic coarctated vehicle-treated (AoCo-V), and aortic coarctated clofibrate-treated (AoCo-C100). The rats were treated for seven days. Blood pressure was measured, and the vascular response to angiotensin II (AngII), norepinephrine (NE), and acetylcholine (ACh) were evaluated in aortic rings. The activity and expression of endothelial nitric oxide synthase (eNOS) was also evaluated. The major findings of this study include the following: AoCo induced a rise in blood pressure, and this effect was attenuated by clofibrate. The vascular response to AngII was higher in aortic rings from the AoCo-V group compared to the Sham-V or AoCo-C100 groups. ACh-elicited vasorelaxation was lower in the arteries of AoCo-V rats than Sham-V or AoCo-C100, while it was comparable between the Sham-V and AoCo-C100 groups. In every case, vasorelaxation was dependent on NO. However, the ACh-induced release of NO as well as NOS activity and expression were reduced in the arteries of AoCo-V rats. Clofibrate maintained normal NOS activity and increased eNOS expression. In conclusion, clofibrate administration attenuated the AoCo-induced rise in blood pressure by a mechanism that involves the participation of the NO system at both the NO synthesis and the eNOS protein expression levels. These events improved endothelial function, preserved normal vascular responses to both vasorelaxants and vasoconstrictors, and led to better blood pressure control.

L-arginine and antioxidant diet supplementation partially restores nitric oxide-dependent regulation of phenylephrine renal vasoconstriction in diabetics rats

OBJECTIVE

The increase of reactive oxygen species (ROS) in diabetes potentiates the vascular effects of phenylephrine through nitric oxide (NO) impairment, facilitating the development of diabetic nephropathy. We propose that the combination of an antioxidant and L-arginine as diet supplements could prevent the increased vascular response to phenylephrine in diabetic animals.

DESIGN

Changes in the adrenergic system play an important role in the development of vascular complications in the prediabetic condition. The vasoconstrictor effects of phenylephrine are regulated by NO, and the impairment of endothelium-dependent vasodilation in diabetes is associated with ROS.

SETTING

Diabetes was induced with a low dose (55 mg/kg body weight) of streptozotocin in 7-week-old rats. Diabetic rats were fed with a diet supplement containing a combination of vitamin E, vitamin C, eicosapentaenoic acid, docosahexaenoic acid, and L-arginine, and the effects on phenylephrine-induced renal vascular responses were evaluated.

RESULTS

Phenylephrine increased the renal perfusion pressure of isolated perfused kidneys from diabetic rats compared with nondiabetic rats. This effect was associated with reduced nitrite release as well as reduced plasma tetrahydrobiopterin and increased superoxide anions in the renal tissue. Diet supplementation with a combination of L-arginine and vitamins in diabetic rats partially prevented the generation of superoxide associated with recovery of the renal release of NO and decreased phenylephrine-induced vasoconstrictor effects, compared with untreated diabetic rats. However, the administration of L-arginine or vitamins alone did not affect phenylephrine-induced vasoconstriction. Vitamin treatment alone did decrease superoxide generation.

CONCLUSION

The protective mechanism of NO on the vasoconstrictor effects of phenylephrine in the kidney is lost during the development of diabetes, probably via the actions of ROS through a decrease in tetrahydrobiopterin, thus contributing to the pathogenesis of diabetic nephropathy. Restoration of this protective NO mechanism can be achieved by simultaneously stimulating NO synthesis and preventing the effects of ROS through the use of L-arginine and a combination of vitamins E and C as diet supplementation.

PPARalpha stimulation exerts a blood pressure lowering effect through different mechanisms in a time-dependent manner

Peroxisome proliferator activated receptors (PPARs) are a family of nuclear receptors that, upon activation with selective ligands, work as transcription factors. Recently, these have been related with the cardiovascular system. Our aim was to study PPARalpha-stimulation and its effects on blood pressure in rats with aortic coarctation, and to explore the role of the antioxidant system. Male Wistar rats (250-280 g) were distributed into the following groups: 1) sham; 2) aortic coarctated-vehicle-treated (AoCo-V), and 3) AoCo-clofibrate (100mg/kg) treated (AoCo-C). Rats were treated for 1 or 21 days. Clofibrate lowered blood pressure in both 1- and 21-day treatments. Renal reactive oxygen species increased after 1 day in AoCo-V, while clofibrate prevented this effect. Superoxide dismutase (SOD)-1 expression increased 3.6-fold upon PPARalpha stimulation (1 day) and returned to normal values by day 21. SOD-1 activity increased slightly in response to clofibrate. Renal activity of catalase increased in AoCo-C (1 day) and returned to normal (21 days). eNOS expression was not modified acutely (1 day) but increased at 21 days of treatment with clofibrate. Angiotensin II AT(1)-receptor expression as well as angiotensin II decreased in clofibrate-treated rats, while angiotensin II AT(2)-receptor expression increased, in both treatment periods. Angiotensin-(1-7) increased at 21 days. Our results suggest that in the early development of AoCo-induced hypertension, stimulation of PPARalpha increases the antioxidant defenses, leading to improvement in endothelial factors while in the sub-chronic phase (21 days), eNOS and angiotensin II receptors appear to play major roles in controlling blood pressure.

Lead exposure effect on angiotensin II renal vasoconstriction

Low levels of chronic lead exposure can produce hypertension and endothelial dysfunction, which could be associated with oxidative stress, changes in vascular tone and an imbalance of endothelial-derived vasoconstriction and vasodilator factors. The aim was to investigate the effect of chronic lead-exposure on angiotensin II-induced vasoconstriction in isolated perfused kidney and microvessels. Male Wistar rats (230-250 g) were treated for 12 weeks with lead acetate (100 ppm, Pbgroup) or pure water (control group). We evaluated the vascular reactivity in the kidneys and renal microvessels in the presence and absence of N(omega)-nitro-L-arginine methyl ester (L-NAME) in both groups. The nitrite concentration in renal perfusate was measured as an index of NO released, renal abundance of 3-nitrotyrosine was measured as well as endothelial NO synthase (eNOS) expression. Oxidative stress was measured by using the oxidative fluorescence dye dihydroethidium (DHE) to evaluate in situ production of superoxide and identified by confocal microscopy. Lead-exposure significantly increased blood pressure, eNOS protein expression, oxidative stress and vascular reactivity to angiotensin II. L-NAME potentiated vascular response to angiotensin II in control group but had no effect on the Pb-group. Nitrites released from the kidney of lead-group was lower compared to the control group while 3-nitrotyrosine was higher. This data suggest that lead-induced hypertension could be caused partially by an altered NOsystem.

Interaction of Endothelial Nitric Oxide and Angiotensin in the Circulation

Discovery of the unexpected intercellular messenger and transmitter nitric oxide (NO) was the highlight of highly competitive investigations to identify the nature of endothelium-derived relaxing factor. This labile, gaseous molecule plays obligatory roles as one of the most promising physiological regulators in cardiovascular function. Its biological effects include vasodilatation, increased regional blood perfusion, lowering of systemic blood pressure, and antithrombosis and anti-atherosclerosis effects, which counteract the vascular actions of endogenous angiotensin (ANG) II. Interactions of these vasodilator and vasoconstrictor substances in the circulation have been a topic that has drawn the special interest of both cardiovascular researchers and clinicians. Therapeutic agents that inhibit the synthesis and action of ANG II are widely accepted to be essential in treating circulatory and metabolic dysfunctions, including hypertension and diabetes mellitus, and increased availability of NO is one of the most important pharmacological mechanisms underlying their beneficial actions. ANG II provokes vascular actions through various receptor subtypes (AT1, AT2, and AT4), which are differently involved in NO synthesis and actions. ANG II and its derivatives, ANG III, ANG IV, and ANG-(1-7), alter vascular contractility with different mechanisms of action in relation to NO. This review article summarizes information concerning advances in research on interactions between NO and ANG in reference to ANG receptor subtypes, radical oxygen species, particularly superoxide anions, ANG-converting enzyme inhibitors, and ANG receptor blockers in patients with cardiovascular disease, healthy individuals, and experimental animals. Interactions of ANG and endothelium-derived relaxing factor other than NO, such as prostaglandin I2 and endothelium-derived hyperpolarizing factor, are also described.

Hypobaric hypoxia induces oxidative stress in rat brain

High altitude exposure results in decreased partial pressure of oxygen and an increased formation of reactive oxygen and nitrogen species (RONS), which causes oxidative damage to lipids, proteins and DNA. Exposure to high altitude appears to decrease the activity and effectiveness of antioxidant enzyme system. The antioxidant system is very less in brain tissue and is very much susceptible to hypoxic stress. The aim of the present study was to investigate the time dependent and region specific changes in cortex, hippocampus and striatum on oxidative stress markers on chronic exposure to hypobaric hypoxia. The rats were exposed to simulated high altitude equivalent to 6100 m in animal decompression chamber for 3 and 7 days. Results indicate an increase in oxidative stress as seen by increase in free radical production, nitric oxide level, lipid peroxidation and lactate dehydrogenase levels. The magnitude of increase in oxidative stress was more in 7 days exposure group as compared to 3 days exposure group. The antioxidant defence system such as reduced glutathione (GSH), glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD) and reduced/oxidized glutathione (GSH/GSSG) levels were significantly decreased in all the three regions. The observation suggests that the hippocampus is more susceptible to hypoxia than the cortex and striatum. It may be concluded that hypoxia differentially affects the antioxidant status in the cortex, hippocampus and striatum.

Enhanced locomotor activity in adult rats with neonatal administration ofN-omega-nitro-L-arginine

Nitric oxide (NO) is a neuronal messenger molecule that plays important roles in the development, maintenance, and functional modifications of brain circuits. We investigated whether the NO levels at different postnatal day (P) periods of the brain develop interference with the locomotion in a novel environment during the postpuberal age (P60). First, using the determination of the nitrite accumulation, we evaluated whether treatment with the NO-synthase inhibitor N-nitro-L-arginine (L-NNA) during different neonatal ages (P1 to P3, P4 to P6, and P7 to P9) affected the levels of NO activity in different regions in the neonatal brain of the rat. We then evaluated whether the locomotor activity in the adult rat (P60) is affected by the blocking of the neonatal NO-activity during a specific period of the development of the nervous system. Neonatal rats with L-NNA administration at P4 to P6 and P7 to P9 show a significant decrease in the levels of NO activity in all the brain regions. However, the blocking of NO synthesis during the neonatal period between P4 to P6 produced an increase in the locomotion after puberty. These data suggest that during a specific step in the development of the brain, the NO levels may play a critical role in the structures that control the spontaneous locomotion in a novel environment after puberty.

Angiotensin II modulates renal sympathetic neurotransmission through nitric oxide in AT2 receptor knockout mice

OBJECTIVE

Angiotensin (Ang) II enhances renal sympathetic neurotransmission and stimulates nitric oxide (NO) release. The present study investigates whether Ang II-mediated modulation of sympathetic neurotransmission is dependent on NO production in the kidney. AT2 -/y receptor-deficient mice are used to identify the Ang II receptor subtype involved.

METHODS

Mice kidneys were isolated and perfused with Krebs-Henseleit solution. Drugs were added to the perfusion solution in a cumulative manner. Release of endogenous noradrenaline (NA) was measured by high-performance liquid chromatography (HPLC). AT1 receptor expression was analysed by real-time polymerase chain reaction (PCR).

RESULTS

Ang II (0.01-30 nmol/l) dose dependently increased pressor responses in kidneys of AT2 -/y mice and wild-type (AT2 +/y) mice. Maximal pressor responses and EC50 values for Ang II was greater in AT2 -/y than in AT2 +/y mice. L-NAME (N(omega)-nitro-L-arginine methyl ester; 0.3 mmol/l) enhanced Ang II-induced pressor responses in both strains. In AT2 -/y mice, Ang II-induced facilitation of NA release was more pronounced than in AT2 +/y mice. L-NAME reduced Ang II-mediated facilitation of NA release in both strains. This reduction was more potent in AT2 -/y mice. In kidneys of AT2 -/y mice the AT1 receptor expression was significantly upregulated.

CONCLUSION

These results suggest that activation of AT1 receptors by Ang II releases NO in mouse kidney to modulate sympathetic neurotransmission. Since AT1 receptors are upregulated in AT2 -/y mice kidneys, NO-dependent effects were greater in these mice. Thus, NO seems to play an important modulatory role for renal sympathetic neurotransmission.

Renal cortex remodeling in nitric oxide deficient rats treated with enalapril

The kidney NO synthase is one of the most important renal controlling systems. This paper aims the quantification of renal cortical components involved in blood pressure regulation under NOs blockade. Spontaneous hypertensive rats (SHRs) are submitted to chronic blockade of NOs by L-nitro-arginine-methyl-ester (L-NAME) and an ACE inhibitor (enalapril) in comparison with the normotensive Wistar rats. Twenty SHRs and 5 Wistar rats were divided in 5 groups and observed for 21 days for blood pressure (BP) and serum creatinine: control Wistar (5) (C-W), control SHR (5) (C-SHR), L-SHR (5)--received L-NAME 30 mg/kg/day, L+E-SHR (5)--received L-NAME and Enalapril maleate 15 mg/kg/day, E-SHR (5)--received Enalapril maleate. A quantitative morphometric study (glomerular density, QA[gl], interstitium volume density, Vv[i], tubular surface and length densities, Sv[t] and Lv[t]) were performed at the end. The BP reached 226+/-15 mmHg in L-SHR group. The BP difference between the L-SHR and the C-SHR groups was significant from the first week while the E-SHR group became significant from the second week. At the end of the experiment the BP of the E-SHR group was similar to the BP in the C-W group. The QA[gl] was similar among C-SHR, L-SHR and L+E-SHR groups and no difference was found between E-SHR and C-W groups. In the L-SHRs serum creatinine was greatly increased, and microscopy showed thickening of arteriolar tunica media with an increase of the wall-to-lumen ratio, perivascular fibrosis, inflammatory infiltrated, tubular atrophy and interstitial fibrosis with focal segmental glomerulosclerosis. The use of enalapril was not completely efficient in reducing BP and morphological injury when the hypertension of SHRs was increased with the NOs blockade suggesting that NO deficiency-induced hypertension is not entirely mediated by the RAAS.

Angiotensin II type 1 receptor blockade restores nitric oxide-dependent renal vascular responses in renovascular hypertension

It was previously reported that enhancement of renal vascular responses to angiotensin II in hypertensive rats is related to decreased release of nitric oxide. Thus, it was suggested that impairment of nitric oxide synthesis during development of hypertension is related to a decreased nitric oxide synthase mRNA expression by an angiotensin II-dependent mechanism. The current study evaluated whether the blockade of angiotensin II type 1 receptor during the development of hypertension restored nitric oxide synthase mRNA expression, nitric oxide synthesis, and nitric oxide-dependent modulation of angiotensin II vasoconstrictor effects. It was shown that losartan treatment prevented increased vascular responses to angiotensin II in hypertensive rats and that this effect was associated with restoration of nitric oxide synthase mRNA expression and nitric oxide synthase activity. Furthermore, angiotensin II-dependent nitric oxide release in hypertensive rats was potentiated by losartan treatment. Angiotensin II (1 microg) released renal nitrites by 485 +/- 178, 470 +/- 150, 185 +/- 45, and 515 +/- 100 nmol/ml/30 s in the kidneys from normotensive, losartan-treated normotensive rats, hypertensive, and losartan-treated hypertensive rats, respectively. The data suggest that during development of hypertension, angiotensin II downregulates nitric oxide synthase mRNA expression, blunting nitric oxide vasodilatory tone and increasing vascular sensitivity to vasoconstrictor agents in the renal circulation.

Nitric oxide and nitric oxide synthases in the fetal cerebral cortex of rats following transient uteroplacental ischemia

The effect of transient uteroplacental ischemia on nitric oxide (NO) levels, enzymatic activity, and expression of NO synthase (NOS) isoforms was studied in fetal rat brains. Fetuses were subjected to ischemia by clamping the uterine arteries for 5 min on gestational day 17 (GD17). At different times after ischemia, fetuses were delivered by Cesarean section under anesthesia to obtain the brains. Transient uteroplacental ischemia produced a time dependent increase in nitrite levels in the brain, reaching a maximum value (300 +/- 25% of baseline) 24 h after uterine artery occlusion and remaining elevated as long as 48 h. Significantly increased nitrite levels were found in the cerebral cortex but not in the mesencephalon and cerebellum. The ischemia-induced increment in nitrite levels was totally blocked by either L-NAME (10 mg/kg) or AMT (0.65 mg/kg) administered i.p. 1 h before uterine artery occlusion. Both Ca(2+)-dependent and Ca(2+)-independent NOS activities in the cerebral cortex remained significantly increased with respect to controls after 24 h following the ischemia. Reverse transcriptase-polymerase chain reaction showed augmented levels of mRNAs for both nNOS and iNOS when compared with controls at 8 h after ischemia. At 36 h, nNOS mRNA returned to basal levels whereas eNOS mRNA levels increased and iNOS mRNA remained elevated. Our results show that the three NOS isoforms participate in increasing NO levels after transient ischemia and suggest a biphasic and differential regulation of the expression of constitutive NOS isoforms in the rat cerebral cortex.

Angiotensin II type AT(2) receptor mRNA expression and renal vasodilatation are increased in renal failure

Kidney failure is associated with changes in renal vascular responses to angiotensin (Ang) II. We characterized expression of Ang II receptors and the renal vasoconstrictor and vasodilator responses to Ang II in kidneys from sham-operated and kidney failure rats. In the isolated perfused kidney of sham-operated rats, Ang II (1, 2, 4, and 8 ng) increased perfusion pressure by 27+/-6, 41+/-10, 54+/-11, and 74+/-12 mm Hg, respectively. These responses were amplified by 62+/-10% (P<0.05) in kidney failure rats. Losartan (1 micromol/L), an angiotensin type 1 (AT(1)) receptor blocker, abolished renal vasoconstriction induced by Ang II, unmasking a renal vasodilatation that was greater in kidney failure rats. CGP-42112 (1 micromol/L) or PD 123,319 (1 micromol/L), angiotensin type 2 (AT(2)) receptor ligands, blunted Ang II-induced renal vasodilatation. In the renal tissue of kidney failure rats, there was a marked increase in expression of AT(1) and AT(2) mRNA receptor. Ang II-induced vasodilatation was blunted by eicosatetraynoic acid (1 micromol/L), the all-purpose inhibitor of arachidonic acid metabolism; clotrimazole (1 micromol/L), an inhibitor of epoxygenase-dependent arachidonic acid metabolism; or Nomega-nitro-L-arginine methyl ester (L-NAME; 1 micromol/L), an inhibitor of NO synthesis. On stimulation with Ang II, 20-HETE was the predominant product released into the renal effluent of sham-operated rats, whereas epoxy-eicosatrienoic acids were the predominant products released into the effluent of kidney failure rats. These data suggest that during development of kidney failure, there is induction of the AT(2) receptors, which may account for increased Ang II-dependent vasodilatation through the predominant release of epoxyeicosatrienoic acids.

Functional and cellular interactions between nitric oxide and prostacyclin

Nitric oxide (NO) and prostacyclin (PGI(2)) can be released by vascular agents to synergize their effects on vascular relaxation. In the present study we assess whether NO could affect PGI(2) production. We evaluated the effect of NO on PGI(2)-mediated arachidonic acid (AA)-induced relaxation in the perfused heart. We used cultured endothelial cells to characterize the mechanism involved in the NO effect on PGI(2) synthesis. AA-induced PGI(2) synthesis was enhanced when NO synthesis was inhibited. NO inhibited AA-induced relaxation and PGI(2) release in the coronary circulation. S-Nitroso-acetyl-DL-penicillamine (SNAP) decreased PGI(2) production in cultured endothelial cells. The SNAP effect was blunted by the inhibitor of soluble guanylate cyclase (LY-83,583) and the blocker of cGMP-dependent protein kinases (H-9). Specific cyclooxygenase-1 (COX-1) immunoprecipitation was associated to co-precipitation of four proteins. COX-1 showed neither serine nor threonine phosphorylation. One of the proteins that co-precipitated with COX-1 presented increased serine phosphorylation in the presence of SNAP. This effect was inhibited by the H-9. We suggest that NO, through cGMP-dependent protein kinases, produces the phosphorylation of a 104-kDa protein that is associated with inhibition in the activity of the COX-1, decreasing PGI(2) synthesis and thereby decreasing coronary PGI(2)-mediated vasodilatation.

Renal vascular interaction of angiotensin II and prostaglandins in renovascular hypertension

The vascular responses to angiotensin II (Ang II) in the renal circulation are increased in kidneys from rats with aortic coarctation compared with sham-operated rats. We have suggested that these differences are related to changes in mediators of the Ang II effect. The aim of this study was to investigate the role of arachidonic acid (AA) metabolites on the Ang II effect in the renal circulation of normotensive and hypertensive rats. We evaluated vascular renal reactivity in the rat isolated perfused kidney. Bolus injection of Ang II (9, 18, 36, 72 ng) increased perfusion pressure in a dose-dependent manner by 16.5+/-4, 23.5+/-4, 35.5+/-7, and 42.5+/-7 mm Hg in sham-operated rats and 50+/-6, 72+/-10, 92+/-6, and 120+/-6 mm Hg in rats with aortic coarctation. Ang II-induced vasoconstriction was prevented in hypertensive rats and potentiated in normotensive rats by the presence of indomethacin (1 microg/ml) in the perfusion solution. Furthermore, the use of the endoperoxide/thromboxane blocker (SQ29548, 1 microM) did not alter the effect of Ang II on the normotensive rats but prevented its effect in hypertensive rats. Moreover, the prostaglandin/ thromboxane (PGH2/TxA2) receptor agonist U46619 increased perfusion pressure to similar values in both kidneys from sham-operated or aortic coarctation rats. Ang II stimulated AA and prostaglandin release from isolated perfused kidneys. However, autacoid release was higher in kidneys from rats with aortic coarctation. In conclusion, we suggest that during the development of hypertension, the AA metabolism of vasoconstrictor prostaglandins is increased, and it mediates the vasoconstrictive effects of Ang II.