Sex-dependent right ventricular hypertrophic gene changes after methamphetamine treatment in mice.

Methamphetamine (MA) abuse is associated with the development of pulmonary arterial hypertension (PAH) and subsequent right ventricular failure. A recent clinical study demonstrated that female sex is a major risk factor for MA-induced PAH. The mechanisms associated with increased prevalence and severity of MA-induced PAH in females are still unclear. We hypothesized that MA may promote changes in gene expression in the right ventricle contributing to the development and/or worsening of PAH in females. Male and female C57BL/6 mice were treated with either MA or vehicle. Right and left ventricular systolic pressures (RVSP and LVSP, respectively) were assessed and tissue samples were collected for gene expression and histology. LVSP and RVSP were not affected by MA in either males or females. Right ventricular hypertrophy was significantly increased by MA in females but it was not affected by MA in males. In the female mice, MA-induced right ventricular hypertrophy was associated with increased expression of brain natriuretic peptide gene and members of the TGF-ß receptor signaling pathway such as TGF-ß receptor-1, smad3 and smad7. In male mice, there were no changes in right ventricular gene expression. Our results suggest that MA caused right ventricular hypertrophy in female mice, but not in males and that this was associated with an increase in hypertrophic genes. The right ventricular hypertrophy was not dependent on increased RVSP suggesting a direct effect of MA on the right ventricle. If this translates to PAH patients, it might explain the poor outcome observed in MA-associated female PAH patients.

Sex Differences in Pulmonary Hypertension.

Pulmonary arterial hypertension (PAH) occurs in women more than men whereas survival in men is worse than in women. In recent years, much research has been carried out to understand these sex differences in PAH. This article discusses clinical and preclinical studies that have investigated the influences of sex, serotonin, obesity, estrogen, estrogen synthesis, and estrogen metabolism on bone morphogenetic protein receptor type II signaling, the pulmonary circulation and right ventricle in both heritable and idiopathic pulmonary hypertension.

Direct Delivery of MicroRNA96 to the Lungs Reduces Progression of Sugen/Hypoxia-Induced Pulmonary Hypertension in the Rat.

The 5HT1B receptor (5HT1BR) contributes to the pathogenic effects of serotonin in pulmonary arterial hypertension. Here, we determine the effect of a microRNA96 (miR96) mimic delivered directly to the lungs on development of severe pulmonary hypertension in rats. Female rats were dosed with sugen (30 mg/kg) and subjected to 3 weeks of hypobaric hypoxia. In normoxia, rats were dosed with either a 5HT1BR antagonist SB216641 (7.5 mg/kg/day for 3 weeks), miR96, or scramble sequence (50 µg per rat), delivered by intratracheal (i.t) administration, once a week for 3 weeks. Cardiac hemodynamics were determined, pulmonary vascular remodeling was assessed, and gene expression was assessed by qRT-PCR, and in situ hybridization and protein expression were assessed by western blot and ELISA. miR96 expression was increased in pulmonary arteries and associated with a downregulation of the 5HT1BR protein in the lung. miR96 reduced progression of right ventricular systolic pressure, pulmonary arterial remodeling, right ventricular hypertrophy, and the occurrence of occlusive pulmonary lesions. Importantly, miR96 had no off-target effects and did not affect fibrotic markers of liver and kidney function. In conclusion, direct delivery of miR96 to the lungs was effective, reducing progression of sugen/hypoxia-induced pulmonary hypertension with no measured off-target effects. miR96 may be a novel therapy for pulmonary arterial hypertension, acting through downregulation of 5HT1BR.

Sex-Dependent Changes in Right Ventricular Gene Expression in Response to Pressure Overload in a Rat Model of Pulmonary Trunk Banding.

Right ventricular hypertrophy (RVH) and subsequent failure are consequences of pulmonary arterial hypertension (PAH). While females are four times more likely to develop PAH, male patients have poorer survival even with treatment, suggesting a sex-dependent dimorphism in right ventricular (RV) hypertrophy/compensation. This may result from differential gene expression in the RV in male vs. female. To date, the sex dependent effect of pressure overload on RV function and changes in gene expression is still unclear. We hypothesize that pressure overload promotes gene expression changes in the RV that may contribute to a poorer outcome in males vs. females. To test this hypothesis, male and female Wistar rats underwent either a sham procedure (sham controls) or moderate pulmonary trunk banding (PTB) (a model of pressure overload induced compensated RV hypertrophy) surgery. Seven weeks post-surgery, RV function was assessed in vivo, and tissue samples were collected for gene expression using qPCR. Compared to sham controls, PTB induced significant increases in the right ventricular systolic pressure, the filling pressure and contractility, which were similar between male and female rats. PTB resulted in an increase in RVH indexes (RV weight, RV weight/tibia length and Fulton index) in both male and female groups. However, RVH indexes were significantly higher in male-PTB when compared to female-PTB rats. Whilst end of procedure body weight was greater in male rats, end of procedure pulmonary artery (PA) diameters were the same in both males and females. RV gene expression analysis revealed that the following genes were increased in PTB-male rats compared with the sham-operated controls: natriuretic peptide A (ANP) and B (BNP), as well as the markers of fibrosis; collagen type I and III. In females, only BNP was significantly increased in the RV when compared to the sham-operated female rats. Furthermore, ANP, BNP and collagen III were significantly higher in the RV from PTB-males when compared to RV from PTB-female rats. Our data suggest that pressure overload-mediated changes in gene expression in the RV from male rats may worsen RVH and increase the susceptibility of males to a poorer outcome when compared to females.

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 Nω-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.

Functional changes in vascular reactivity to adenosine receptor activation in type I diabetic mice.

Activation of adenosine receptors has been implicated in several biological functions, including cardiovascular and renal function. Diabetes causes morphological and functional changes in the vasculature, resulting in abnormal responses to various stimuli. Recent studies have suggested that adenosine receptor expression and signaling are altered in disease states such as hypertension, diabetes. Using a streptozotocin (STZ) mouse model of type I diabetes (T1D), we investigated the functional changes in aorta and resistance mesenteric arteries to adenosine receptor agonist activation in T1D. Organ baths and DMT wire myographs were used for muscle tension measurements in isolated vascular rings, and western blotting was used for protein analysis. Concentration response curves to selective adenosine receptor agonists, including CCPA (A1 receptor agonist), Cl-IBMECA (A3 receptor agonist), CGS-21680 (A2A receptor agonist), and BAY 60-6583 (A2B receptor agonist), were performed. We found that diabetes did not affect adenosine receptor agonist-mediated relaxation or contraction in mesenteric arteries. However, aortas from diabetic mice exhibited a significant decrease (P < 0.05) in A1 receptor-mediated vasoconstriction. In addition, the aortas from STZ-treated mice exhibited an increase in phenylephrine-mediated contraction (EC50 7.40 ± 0.08 in STZ vs 6.89 ± 0.14 in vehicle; P < 0.05), while relaxation to A2A receptor agonists (CGS-21680) tended to decrease in aortas from the STZ-treated group (not statistically significant). Our data suggest that changes in adenosine receptor(s) vascular reactivity in T1D is tissue specific, and the decrease in A1 receptor-mediated aortic contraction could be a compensatory mechanism to counterbalance the increased adrenergic vascular contractility observed in aortas from diabetic mice.

Divergent coronary flow responses to uridine adenosine tetraphosphate in atherosclerotic ApoE knockout mice.

Uridine adenosine tetraphosphate (Up4A) exerts potent relaxation in porcine coronary arteries that is reduced following myocardial infarction, suggesting a crucial role for Up4A in the regulation of coronary flow (CF) in cardiovascular disorders. We evaluated the vasoactive effects of Up4A on CF in atherosclerosis using ApoE knockout (KO) mice ex vivo and in vivo. Functional studies were conducted in isolated mouse hearts using the Langendorff technique. Immunofluorescence was performed to assess purinergic P2X1 receptor (P2X1R) expression in isolated mouse coronary arteries. In vivo effects of Up4A on coronary blood flow (CBF) were assessed using ultrasound. Infusion of Up4A (10-9-10-5 M) into isolated mouse hearts resulted in a concentration-dependent reduction in CF in WT and ApoE KO mice to a similar extent; this effect was exacerbated in ApoE KO mice fed a high-fat diet (HFD). The P2X1R antagonist MRS2159 restored Up4A-mediated decreases in CF more so in ApoE KO + HFD than ApoE KO mice. The smooth muscle to endothelial cell ratio of coronary P2X1R expression was greater in ApoE KO + HFD than ApoE KO or WT mice, suggesting a net vasoconstrictor potential of P2X1R in ApoE KO + HFD mice. In contrast, Up4A (1.6 mg/kg) increased CBF to a similar extent among the three groups. In conclusion, Up4A decreases CF more in ApoE KO + HFD mice, likely through a net upregulation of vasoconstrictor P2X1R. In contrast, Up4A increases CBF in vivo regardless of the atherosclerotic model.

Angeli's Salt, a nitroxyl anion donor, reverses endothelin-1 mediated vascular dysfunction in murine aorta.

Nitroglycerin (Gtn) is a treatment for cardiovascular patients due to its vasodilatory actions, but induces tolerance when given chronically. A proposed mechanism is the superoxide (O2-)-oxidative stress hypothesis, which suggests that Gtn increases O2- production. Nitric oxide (NO) exists in three different redox states; the protonated, reduced state, nitroxyl anion (HNO) is an emerging candidate in vascular regulation. HNO is resistant to scavenging and of particular interest in conditions where high levels of reactive oxygen species (ROS) exist. We hypothesize that treatment with Gtn will exacerbate endothelin 1 (ET-1) induced vascular dysfunction via an increase in ROS, while treatment with Angeli's Salt (AS), an HNO donor, will not. Aorta from mice were isolated and divided into four groups: vehicle, ET-1 [0.1µM, 1µM], ET-1+Gtn [Gtn 1µM] and ET-1+AS [AS 1µM]. Concentration response curves (CRCs) to acetylcholine (ACh) and phenylephrine (Phe) were performed. Aorta incubated with ET-1 (for 20-22h) exhibited a decreased relaxation response to ACh and an increase in Phe-mediated contraction. Aorta incubated with AS exhibited a reversal in ET-1 induced vascular and endothelial dysfunction. ET-1 increased ROS in aortic vascular smooth muscle cells (VSMCs), visualized by dihydroethidium (DHE) staining. AS incubated reduced this ROS generation, yet maintained with Gtn treatment. These data suggest that aorta incubated with the HNO donor, AS, can reverse ET-1 mediated vascular dysfunction, which may be through a decrease or prevention of ROS generation. We propose that HNO may be vasoprotective and that HNO donors studied as a therapeutic option where other organic nitrates are contraindicative.

Nitroxyl Anion Mediates Relaxation in Mesenteric Arteries from Angiotensin II Hypertensive Mice.

AIMS: Nitroxyl anion (HNO) has recently become an emerging candidate in vascular regulation. NO- is a potent vasodilator of both conduit and small resistance vessels and mediates relaxation in a soluble guanylate cyclase-dependent manner. Interestingly, HNO activates voltage-dependent K+ (K+ V) channels, whereas Nitric Oxide (NO) activates calcium-activated K+ Ca channels. To date, there are few studies investigating the role of HNO in hypertension, and the possible mechanisms, which may be altered during this condition. We hypothesized that mesenteric arteries from angiotensin II-induced (AngII) hypertensive mice would exhibit an increased dependence upon NO- for relaxation, which may be mediated through K+ V channels. Methods and Key Results: C57/Bl6 mice, aged 12-14 weeks were implanted with mini-pumps containing angiotensin II (AngII, 3600ng/kg/min) for 14 days. For this study, we proposed to investigate the role of HNO in the resistance vasculature, and so first order mesenteric arteries were isolated and used in functional studies, or were frozen for Western blot analysis. We observed that mesenteric arteries from AngII mice (AngII) exhibited a decrease in HNO-mediated relaxation, which was endotheliumindependent. With HNO scavenging by L-cysteine [3mM], the maximal acetylcholine (ACh)-mediated relaxation response was decreased in sham, whereas mesenteric arteries from AngII exhibited a decrease in sensitivity. Incubation with the K+ V channel inhibitor, 4-aminopyridine [1mM], decreased AChmediated relaxation responses in sham, but almost completely abolished relaxation in AngII. CONCLUSION: We reveal that exogenous HNO-mediated relaxation, via Angeli's Salt, is impaired in mesenteric arteries from AngII-treated mice, yet endogenous HNO-mediated relaxation may be more important during hypertension.

Coronary microvascular disease as an early culprit in the pathophysiology of diabetes and metabolic syndrome.

Metabolic syndrome (MetS) is a group of cardio-metabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia; these are also a combination of independent coronary artery disease (CAD) risk factors. Alarmingly, the prevalence of MetS risk factors are increasing and a leading cause for mortality. In the vasculature, complications from MetS and type 2 diabetes (T2D) can be divided into microvascular (retinopathy and nephropathy) and macrovascular (cardiovascular diseases and erectile dysfunction). In addition to vascular and endothelial dysfunction, vascular remodeling and stiffness are also hallmarks of cardiovascular disease (CVD), and well-characterized vascular changes that are observed in the early stages of hypertension, T2D, and obesity [1-3]. In the heart, the link between obstructive atherosclerosis of coronary macrovessels and myocardial ischemia (MI) is well established. However, recent studies show that abnormalities in the coronary microcirculation are associated with functional and structural changes in coronary microvessels (classically defined as being ≤150-200µm internal diameter), which may cause or contribute to MI even in the absence of obstractive CAD. This suggests a prognostic value of an abnormal coronary microcirculation as an early sub-clinical culprit in the pathogenesis and progression of heart disease in T2D and MetS. The aim of this review is to summarize recent studies investigating the coronary microvascular remodeling in an early pre-atherosclerotic phase of MetS and T2D, and to explore potential mechanisms associated with the timing of coronary microvascular remodeling relative to that of the macrovasculature.

Role of Adenosine Receptor(s) in the Control of Vascular Tone in the Mouse Pudendal Artery.

Activation of adenosine receptors (ARs) has been implicated in the modulation of renal and cardiovascular systems, as well as erectile functions. Recent studies suggest that adenosine-mediated regulation of erectile function is mainly mediated through A2BAR activation. However, no studies have been conducted to determine the contribution of AR subtype in the regulation of the vascular tone of the pudendal artery (PA), the major artery supplying and controlling blood flow to the penis. Our aim was to characterize the contribution of AR subtypes and identify signaling mechanisms involved in adenosine-mediated vascular tone regulation in the PA. We used a DMT wire myograph for muscle tension measurements in isolated PAs from wild-type, A2AAR knockout, A2BAR knockout, and A2A/A2BAR double-knockout mice. Real-time reverse transcription-polymerase chain reaction was used to determine the expression of the AR subtypes. Data from our pharmacologic and genetic approaches suggest that AR activation-mediated vasodilation in the PA is mediated by both the A2AAR and A2BAR, whereas neither the A1AR nor A3AR play a role in vascular tone regulation of the PA. In addition, we showed that A2AAR- and A2BAR-mediated vasorelaxation requires activation of nitric oxide and potassium channels; however, only the A2AAR-mediated response requires protein kinase A activation. Our data are complemented by mRNA expression showing the expression of all AR subtypes with the exception of the A3AR. AR signaling in the PA may play an important role in mediating erection and represent a promising therapeutic option for the treatment of erectile dysfunction.

Enhanced A2A adenosine receptor-mediated increase in coronary flow in type I diabetic mice.

Adenosine A2A receptor (A2AAR) activation plays a major role in the regulation of coronary flow (CF). Recent studies from our laboratory and others have suggested that A2AAR expression and/or signaling is altered in disease conditions. However, the coronary response to AR activation, in particular A2AAR, in diabetes is not fully understood. In this study, we use an STZ mouse model of type 1 diabetes (T1D) to look at CF responses to the nonspecific AR agonist NECA and the A2AAR specific agonist CGS 21680 in-vivo and ex-vivo. Using immunofluorescence, we also explored the effect of diabetes on A2AAR expression in coronary arteries. NECA mediated increase in CF was significantly increased in hearts isolated from STZ-induced diabetic mice. In addition, both in in-vivo and ex-vivo responses to A2AAR activation using CGS 21680 were significantly higher in diabetic mice when compared to their controls. Immunohistochemistry showed an upregulation of A2AAR in both coronary smooth muscle and endothelial cells (~160% and ~140%, respectively). Our data suggest that diabetes resulted in an increased A2AAR expression in coronary arteries which resulted in enhanced A2AAR-mediated increase in CF observed in diabetic hearts. This is the first report implying that A2AAR has a role in the regulation of CF in diabetes, supporting recent studies suggesting that the use of adenosine and its A2A selective agonist (regadenoson, Lexiscan®) may not be appropriate for the detection of coronary artery diseases in T1D and the estimation of coronary reserve.

Involvement of NADPH oxidase in A2A adenosine receptor-mediated increase in coronary flow in isolated mouse hearts.

Adenosine increases coronary flow mainly through the activation of A2A and A2B adenosine receptors (ARs). However, the mechanisms for the regulation of coronary flow are not fully understood. We previously demonstrated that adenosine-induced increase in coronary flow is in part through NADPH oxidase (Nox) activation, which is independent of activation of either A1 or A3ARs. In this study, we hypothesize that adenosine-mediated increase in coronary flow through Nox activation depends on A2A but not A2BARs. Functional studies were conducted using isolated Langendorff-perfused mouse hearts. Hydrogen peroxide (H2O2) production was measured in isolated coronary arteries from WT, A2AAR knockout (KO), and A2BAR KO mice using dichlorofluorescein immunofluorescence. Adenosine-induced concentration-dependent increase in coronary flow was attenuated by the specific Nox2 inhibitor gp91 ds-tat or reactive oxygen species (ROS) scavenger EUK134 in both WT and A2B but not A2AAR KO isolated hearts. Similarly, the A2AAR selective agonist CGS-21680-induced increase in coronary flow was significantly blunted by Nox2 inhibition in both WT and A2BAR KO, while the A2BAR selective agonist BAY 60-6583-induced increase in coronary flow was not affected by Nox2 inhibition in WT. In intact isolated coronary arteries, adenosine-induced (10 µM) increase in H2O2 formation in both WT and A2BAR KO mice was attenuated by Nox2 inhibition, whereas adenosine failed to increase H2O2 production in A2AAR KO mice. In conclusion, adenosine-induced increase in coronary flow is partially mediated by Nox2-derived H2O2, which critically depends upon the presence of A2AAR.

Metformin treatment improves erectile function in an angiotensin II model of erectile dysfunction.

INTRODUCTION: Increased angiotensin II (AngII) levels cause hypertension, which is a major risk factor for erectile dysfunction (ED). Studies have demonstrated that increased AngII levels in penile tissue are associated with ED. A recent study showed that metformin treatment restored nitric oxide synthase (NOS) protein expression in penile tissue in obese rats; however, whether metformin treatment can be beneficial and restore erectile function in a model of ED has not yet been established. AIM: The goal of this study was to test the hypothesis that AngII induces ED by means of increased corpus cavernosum contraction, and that metformin treatment will reverse ED in AngII-treated rats. METHODS: Male Sprague-Dawley rats were implanted with mini-osmotic pumps containing saline or AngII (70 ng/minute, 28 days). Animals were then treated with metformin or vehicle during the last week of AngII infusion. MAIN OUTCOME MEASURES: Intracavernosal pressure; corpus cavernosum contraction and relaxation; nNOS protein expression; extracellular signal-regulated kinase (ERK1/2), AMP-activated protein kinase (AMPK), and eNOS protein expression and phosphorylation. RESULTS: AngII-induced ED was accompanied with an increase in corpus cavernosum contractility, decreased nitrergic relaxation, and increased ERK1/2 phosphorylation. Metformin treatment improved erectile function in the AngII-treated rats by reversing the increased contraction and decreased relaxation. Metformin treatment also resulted in an increase in eNOS phosphorylation at ser1177. CONCLUSIONS: Metformin treatment increased eNOS phosphorylation and improved erectile function in AngII hypertensive rats by reestablishing normal cavernosal smooth muscle tone.

New insights into hypertension-associated erectile dysfunction.

PURPOSE OF REVIEW: Erectile dysfunction is recognized as a quality-of-life disorder that needs to be treated. Currently, it is estimated to affect as many as 30 million American men. Thirty percent of hypertensive patients complain of erectile dysfunction. The understanding of common mechanisms involved in the cause of erectile dysfunction associated with hypertension, and the investigation of antihypertensive drugs that impact erectile dysfunction, will provide important tools toward identifying new therapeutic targets that will improve the quality of life for patients in these conditions. RECENT FINDINGS: Hypertension and erectile dysfunction are closely intertwined diseases, which have endothelial dysfunction as a common base. During hypertension and/or erectile dysfunction, disturbance of endothelium-derived factors can lead to an increase in vascular smooth muscle (VSM) contraction. Hypertension can lead to erectile dysfunction as a consequence of high blood pressure (BP) or due to antihypertensive treatment. However, growing evidence suggests erectile dysfunction is an early sign for hypertension. Also, some phosphodiesterase-5 inhibitors used to treat erectile dysfunction can improve BP, but the link between these conditions has not been totally understood. SUMMARY: This review will discuss the interplay between hypertension and erectile dysfunction, exploring newest insights regarding hypertension-associated erectile dysfunction, as well as the effect of antihypertensive drugs in erectile dysfunction patients.

Aorta from angiotensin II hypertensive mice exhibit preserved nitroxyl anion mediated relaxation responses.

Hypertension is a disorder affecting millions worldwide, and is a leading cause of death and debilitation in the United States. It is widely accepted that during hypertension and other cardiovascular diseases the vasculature exhibits endothelial dysfunction; a deficit in the relaxatory ability of the vessel, attributed to a lack of nitric oxide (NO) bioavailability. Recently, the one electron redox variant of NO, nitroxyl anion (NO(-)) has emerged as an endothelium-derived relaxing factor (EDRF) and a candidate for endothelium-derived hyperpolarizing factor (EDRF). NO(-) is thought to exist protonated (HNO) in vivo, which would make this species more resistant to scavenging. However, no studies have investigated the role of this redox species during hypertension, and whether the vasculature loses the ability to relax to HNO. Thus, we hypothesize that aorta from angiotensin II (AngII)-hypertensive mice will exhibit a preserved relaxation response to Angeli's Salt, an HNO donor. Male C57Bl6 mice, aged 12-14 weeks were implanted with mini-osmotic pumps containing AngII (90ng/min, 14 days plus high salt chow) or sham surgery. Aorta were excised, cleaned and used to perform functional studies in a myograph. We found that aorta from AngII-hypertensive mice exhibited a significant endothelial dysfunction as demonstrated by a decrease in acetylcholine (ACh)-mediated relaxation. However, vessels from hypertensive mice exhibited a preserved response to Angeli's Salt (AS), the HNO donor. To confirm that relaxation responses to HNO were maintained, concentration response curves (CRCs) to ACh were performed in the presence of scavengers to both NO and HNO (carboxy-PTIO and L-cys, resp.). We found that ACh-mediated relaxation responses were significantly decreased in aorta from sham and almost completely abolished in aorta from AngII-treated mice. Vessels incubated with l-cys exhibited a modest decrease in ACh-mediated relaxations responses. These data demonstrate that aorta from AngII-treated hypertensive mice exhibit a preserved relaxation response to AS, an HNO donor, regardless of a significant endothelial dysfunction.

Interleukin 6 knockout prevents angiotensin II hypertension: role of renal vasoconstriction and janus kinase 2/signal transducer and activator of transcription 3 activation.

Chronic angiotensin II (Ang II) infusion stimulates interleukin (IL) 6 release, and we and others have shown that preventing the increase in IL-6 significantly attenuates Ang II hypertension. This study measured renal blood flow (RBF) chronically, using Transonic flow probes in wild-type (WT) and IL-6 knockout (KO) mice, to determine the role of RBF regulation in that response. Ang II infusion at 200, 800, and 3600 ng/kg per minute caused a dose-dependent decrease in RBF in WT mice, and the response at 800 ng/kg per minute was compared between WT and IL-6 KO mice. Ang II infusion increased plasma IL-6 concentration in WT mice and increased mean arterial pressure (19 h/d with telemetry) from 113±4 to 149±4 mm Hg (Δ36 mm Hg) over the 7-day infusion period, and that effect was blocked in IL-6 KO mice (119±7 to 126±7 mm Hg). RBF decreased to an average of 61±8% of control over the 7-day period (control: 0.86±0.02 mL/min) in the WT mice; however, the average decrease to 72±6% of control (control: 0.88±0.02 mL/min) in the KO mice was not significantly different. There also was no difference in afferent arteriolar constriction by Ang II in blood-perfused juxtamedullary nephrons in WT versus KO mice. Phosphorylation of janus kinase 2 and signal transducer and activator of transcription 3 in renal cortex homogenates increased significantly in Ang II-infused WT mice, and that effect was prevented completely in Ang II-infused IL-6 KO mice. These data suggest that IL-6-dependent activation of the renal janus kinase 2/signal transducer and activator of transcription 3 pathway plays a role in Ang II hypertension but not by mediating the effect of Ang II to decrease total RBF.

Lack of blood pressure salt-sensitivity supports a preglomerular site of action of nitric oxide in Type I diabetic rats.

1. The relationship between sodium intake and blood pressure is affected differently by changes in angiotensin (Ang) II and preglomerular resistance, and this study measured that relationship to evaluate the link between nitric oxide and blood pressure early in diabetes. 2. Rats were chronically instrumented, placed on high-sodium (HS = 12 mEq/d) or low-sodium (LS = 0.07 mEq/d) intake diets and assigned to either vehicle- (V) or Nomega-nitro-L-arginine methyl ester- (L-NAME; L) treated groups. Mean arterial pressure (MAP) was measured 18 h/day for a 6-day control and 14-day streptozotocin diabetic period in each animal. 3. The MAP of the control period averaged 95 +/- 1 and 94 +/- 1 mmHg in the LSV and HSV rats and 116 +/- 2 and 124 +/- 1 mmHg in the LSL and HSL rats, respectively (LSL vs HSL was significant at P < 0.05). Diabetes increased MAP only in the LSL and HSL rats to 141 +/- 2 mmHg and 152 +/- 2, respectively, similar to our previous reports, and those respective 25 and 28 mmHg increases were a parallel shift in the pressure natriuresis relationship. However, the apparent difference between the LSL and HSL groups when compared was a parallel of the control MAP difference. Plasma renin activity (PRA) in the control period averaged 1.5 +/- 0.5 and 8.1 +/- 1.8 ng AI/mL per h in the HSV and LSV rats, and 0.8 +/- 0.2 and 2.8 +/- 0.5 ng AI/mL per h in the HSL and LSL rats, respectively, and increased similarly by 4.6-fold in the HSL and 4.8-fold in the LSL rats during diabetes. Glomerular filtration rate (GFR) increased in the vehicle but not the L-NAME-treated groups, consistent with our previous reports. 4. Thus, the hypertension caused by the onset of diabetes in L-NAME-treated rats was not salt-sensitive. The normal modulation of PRA by salt intake and the failure of GFR to increase are consistent with our hypothesis that nitric oxide may protect against hypertension early in diabetes by preventing preglomerular vasoconstriction by AngII.

Angiotensin II hypertension is attenuated in interleukin-6 knockout mice.

Plasma levels of IL-6 correlate with high blood pressure under many circumstances, and ANG II has been shown to stimulate IL-6 production from various cell types. This study tested the role of IL-6 in mediating the hypertension caused by high-dose ANG II and a high-salt diet. Male C57BL6 and IL-6 knockout (IL-6 KO) mice were implanted with biotelemetry devices and placed in metabolic cages to measure mean arterial pressure (MAP), heart rate (HR), sodium balance, and urinary albumin excretion. Baseline MAP during the control period averaged 114 +/- 1 and 109 +/- 1 mmHg for wild-type (WT) and IL-6 KO mice, respectively, and did not change significantly when the mice were placed on a high-salt diet (HS; 4% NaCl). ANG II (90 ng/min sc) caused a rapid increase in MAP in both groups, to 141 +/- 9 and 141 +/- 4 in WT and KO mice, respectively, on day 2. MAP plateaued at this level in KO mice (134 +/- 2 mmHg on day 14 of ANG II) but began to increase further in WT mice by day 4, reaching an average of 160 +/- 4 mmHg from days 10 to 14 of ANG II. Urinary albumin excretion on day 4 of ANG II was not different between groups (9.18 +/- 4.34 and 8.53 +/- 2.85 microg/2 days for WT and KO mice). By day 14, albumin excretion was nearly fourfold greater in WT mice, but MAP dropped rapidly back to control levels in both groups when the ANG II was stopped after 14 days. Thus the approximately 30 mmHg greater ANG II hypertension in the WT mice suggests that IL-6 contributes significantly to ANG II-salt hypertension. In addition, the early separation in MAP, the albumin excretion data, and the rapid, post-ANG II recovery of MAP suggest an IL-6-dependent mechanism that is independent of renal injury.