DOCA-salt Model Of Hypertension Research Articles

Abstract 15056: The Activation of Angiotensin II Type1a Receptors in the SFO and PVN is Necessary to Prime Immunity in Salt Sensitive Hypertension

Introduction: Salt sensitive hypertension (HTN) is associated with increased salt intake and elevated activity of the renin-angiotensin system (RAS) in the brain. We have found that DOCA-salt HTN partly depends on a sympathetic-mediated PlGF release in the spleen. Hypothesis: Whether this effect is related to the contribution of RAS signaling in brain nuclei mediating HTN responses is poorly known. We hypothesized that angiotensin type 1a receptors (AT1aR) within the circumventricular organs (CVOs) could mediate DOCA-salt hypertensive responses. Methods: To discriminate between CVOs, we used 3 mouse model with deletion of AT1aR in 3 in brain CVOs. AT1aRfloxed mice were 1) stereotaxically injected with an adenovirus encoding a Cre-recombinase (or GFP as control), directly in the subfornical organ (SFO), or 2) crossed with Sim1Cre+ (and Sim1Cre- as control) mice to delete the gene in the paraventricular nucleus of hypothalamus (PVN) or 3) crossed with Phox2bCre+ (and Phox2bCre- as control) mice to delete the gene in the dorsal motor nucleus of the vagus nerve (DMV). T Results: We implanted mice with pellets of DOCA or placebo, as control, and salt in drinking water for 3 weeks finding that: AT1aRfloxed mice + Virus encoding Cre Recombinase in the SFO and AT1aRfloxed;Sim1Cre+ mice were protected form HTN-DOCA-salt (SFO-SBP mmHg :133±1 vs 106±0,6, ***p>0,0001; PVN-SBP mmHg :144±2 vs 112±2,***p>0,0001 respectively to their controls); whereas AT1aRfloxed;Phox2bCre+ mice had increased blood pressure levels (SBP mmHg :144±1 vs 144±0,7, respectively to control mice). Additionally, deletion of AT1aR in the SFO and PVN attenuated egression of T cells from the spleen and infiltration on target organ with a reduced disruption of renal glomeruli and reduced accumulation of matrix protein in response to DOCA-salt (SFO-Bowman’s size μm 2 1761±150 vs 821±78, respectively, **p<0,001; PVN-Bowman’s size μm 2 3927±212 vs 2805±252, respectively, **p<0,001). Mice KO for AT1aR in the DMV were not protected from organ damage (Bowman’s size μm 2 776 ± 104 vs 1090 ± 94, respectively). Conclusions: ogether, these data indicate that SFO and PVN contribute to blood pressure in the DOCA-salt model of hypertension through AT1aR signaling, while the DMV role was independent from AT1aR.

P2Y2 receptor decreases blood pressure by inhibiting ENaC.

Stimulating the Gq-coupled P2Y2 receptor (P2ry2) lowers blood pressure. Global knockout of P2ry2 increases blood pressure. Vascular and renal mechanisms are believed to participate in P2ry2 effects on blood pressure. To isolate the role of the kidneys in P2ry2 effects on blood pressure and to reveal the molecular and cellular mechanisms of this action, we test here the necessity of the P2ry2 and the sufficiency of Gq-dependent signaling in renal principal cells to the regulation of the epithelial Na+ channel (ENaC), sodium excretion, and blood pressure. Activating P2ry2 in littermate controls but not principal cell-specific P2ry2-knockout mice decreased the activity of ENaC in renal tubules. Moreover, deletion of P2ry2 in principal cells abolished increases in sodium excretion in response to stimulation of P2ry2 and compromised the normal ability to excrete a sodium load. Consequently, principal cell-specific knockout of P2ry2 prevented decreases in blood pressure in response to P2ry2 stimulation in the deoxycorticosterone acetate-salt (DOCA-salt) model of hypertension. In wild-type littermate controls, such stimulation decreased blood pressure in this model of hypertension by promoting a natriuresis. Pharmacogenetic activation of Gq exclusively in principal cells using targeted expression of Gq-designer receptors exclusively activated by designer drugs and clozapine N-oxide decreased the activity of ENaC in renal tubules, promoting a natriuresis that lowered elevated blood pressure in the DOCA-salt model of hypertension. These findings demonstrate that the kidneys play a major role in decreasing blood pressure in response to P2ry2 activation and that inhibition of ENaC activity in response to P2ry2-mediated Gq signaling lowered blood pressure by increasing renal sodium excretion.

Abstract 45: Sex Differences Of Renal11β-hsd1 And 11β-hsd2 Expression In A Doca-salt Model Of Hypertension.

The balance between hydroxysteroid dehydrogenase 1 (11β-HSD1) and hydroxysteroid dehydrogenase 2 (11β-HSD2) have been implicated in the regulation of mineralocorticoid effects. We have previously shown in the DOCA-salt model of hypertension that males have a more pro-inflammatory immune profile and higher BP than females. The current study tested the hypothesis that males have a higher ratio of 11β -HSD1 to 11β -HSD2 and that preventing DOCA-salt induced increases in BP significantly shifts that ratio.At 10 wks of age, male and female Sprague-Dawley rats were anesthetized and a right uni-nephrectomy (UNX) was performed. After one week of recovery, rats were randomized to the following groups: 1) UNX controls, 2) DOCA-salt (200 mg) with 0.9% saline to drink, or 3) DOCA-salt with saline + hydrochlorothiazide (HCTZ; 55 mg/kg/day) and reserpine (RES; 4.5 mg/kg/day. After 3 weeks of treatment, the remaining kidney was isolated to measure mRNA expression of 11β-HSD1 and 11β-HSD2 via RT-qPCR.Control UNX males had a higher 11β-HSD1:11β-HSD2 ratio than females (0.9 ± 0.15 vs 0.3 ± 0.04; P=0.02). After DOCA-salt, 11β-HSD1 increased in both males and females (2.5 ± 0.1 vs. 1.3 ± 0.08; P treatment <0.0001). Males maintained a higher 11β-HSD1:11β-HSD2 ratio as well has had a higher increase in 11β-HSD1 to 11β-HSD2 ratio than females (P sex =0.04; P interaction =0.04) after DOCA-salt. With HCTZ/RES treatment, 11β-HSD1 to 11β-HSD2 ratios significantly decreased in both males and females (1.9 ± 0.5 vs. 0.8 ± 0.09; P treatment =0.002), but males maintained a higher 11β-HSD1:11β-HSD2 ratio vs females (P sex =0.002; P interaction =0.54). Our data suggests that there are sex differences in the balance of renal mRNA expression of 11β-HSD1 and 11β-HSD2, with males having a greater 11β-HSD1:11β-HSD2 ratio compared to females. Preventing DOCA-salt induced increases in BP significantly shifts this ratio through an upregulation of 11β-HSD2 in both sexes.

Abstract MP04: Interleukin-33 Drives Cardiac Remodeling And Alters Macrophage Polarization In Doca-salt Hypertension

Interleukin-33 (IL-33) is an alarmin critical for alternative macrophage activation and has been linked to hypertension in humans. The goal of this study was to evaluate whether IL-33 contributes to (deoxycorticosterone acetate) DOCA-salt induced cardiac remodeling and macrophage polarization. C57Bl/6J (WT, n=8) and IL33-deficient (IL-33 KO, n=8) mice underwent uninephrectomy, implantation of a DOCA pellet, and 1% NaCl supplementation of drinking water for three weeks. A control group of WT mice (n=10) underwent a sham procedure and were maintained on normal water. Systolic blood pressure measured by tail cuff showed a significant increase in WT DOCA-salt mice (128±9 mmHg; mean±SD) and IL-33 KO DOCA-salt mice (129±11) compared to WT sham (103±11). Hypertension was accompanied by significantly increased heart to body weight ratios in WT DOCA-salt (7.0±1.0 mg/g) and IL-33 KO DOCA-salt (6.8±0.6) compared to WT sham (5.3±0.3) mice. Glomerular injury was assessed by urine albumin-to-creatinine ratios, which were similarly increased in WT DOCA-salt (0.92±0.4) and IL-33 KO DOCA-salt (0.42±0.09) mice compared to WT controls (0.03±0.003). Echocardiography was performed to assess left ventricle (LV) dimensions and systolic function. IL-33 KO DOCA-salt mice exhibited a significantly higher cardiac output (22±2 mL/min) compared to WT sham (16±3) and WT DOCA-salt (15±3) mice, driven by increased stroke volume. No significant changes in heart rate or ejection fraction were observed between groups. Additionally, IL33-KO DOCA-salt mice had an increased diastolic LV internal dimension (3.2±0.2 mm) compared to WT sham (2.7±0.3) and WT DOCA-salt (2.7±0.3). DOCA-salt induced increased mRNA expression of alternative macrophage activation markers in both LV ( Chil3, Il10) and isolated peritoneal macrophages ( Arg1, Retnla, Tgfb1 ). Peritoneal macrophages deficient in IL-33 expressed less Il10 compared to WT. Cardiac fibrosis evaluated by Masson’s trichrome showed a significant increase in LV collagen deposition in WT DOCA-salt mice (1.09±0.8% trichrome positive) compared to WT sham (0.43±0.3) but no increase in IL-33 KO DOCA-salt mice (0.54±0.3). In conclusion, IL-33 deficiency alters macrophage and cardiac function in the DOCA-salt model of hypertension.

Abstract MP57: Chronic Inhibition Of Brain Rhomboid-like Protein 2 (irhom2) Activity Decreases Arterial Blood Pressure In Salt-sensitive Hypertension In Mice

We previously reported that ADAM17 (aka tumor necrosis factor-α convertase) is critical for the development of hypertension in experimental models and patients. Recent studies highlighted that ADAM17’s formation of TNF-α relies on prior maturation of this sheddase, controlled by the rhomboid-like protein 2 (iRhom2) specifically in microglia. Genetic deletion of iRhom2 in mice shows significant attenuation of TNF-α and ADAM17 activity in a tissue specific manner. Here, we hypothesized that silencing iRhom2 activity specifically in the brain would decrease blood pressure (BP) in the DOCA-salt model of hypertension, in mice. Uninephrectomized mice were implanted subcutaneously (sc) with DOCA-pellets (50 mg) and provided with 1% saline in drinking water. In addition, mice were chronically implanted with an icv cannula connected to a sc osmotic minipump for delivery of: (1) iRhom2-siRNA (9.6 μg/kg/day), (2) scrambled siRNA (SCR 0.2 μg/kg/day), (3) ADAM17 antibody (ADAM17-Ab; 23.8 μg/kg/day) or (4) artificial cerebrospinal fluid (aCSF) for 2 weeks while BP was recorded by telemetry. DOCA-salt treatment led to a significant increase in BP in the control groups (SCR: 156 ±3 mmHg and aCSF: 161 ±1 mmHg; n=3/group; p<0.001) compared to baseline values (122 ±2 mmHg; n=12). ICV infusion of iRhom2-siRNA or ADAM17 neutralizing antibody for 2-weeks in DOCA-salt-treated mice resulted in a significant attenuation of BP (iRhom2-siRNA: 152 ±2 mmHg and ADAM17-Ab: 151 ±2 mmHg n=3/group, p<0.001). These data suggest that: 1) Selective silencing of iRhom2 from microglia is as potent as ADAM17 neutralization throughout the brain in lowering BP and 2) iRhom2 is a potential new therapeutic target for the treatment of salt-sensitive hypertension.

Oral L‐arginine treatment significantly reduces blood pressure without altering the renal T cell profile in the DOCA salt model of hypertension

The immune system plays a critical role in the development of hypertension. Our lab has previously reported that there is a sex difference in the renal T cell profile in DOCA salt hypertension, with males having more pro‐inflammatory Th17 cells, whereas females have more anti‐inflammatory regulatory T cells (Tregs). DOCA treated males also have a greater blood pressure (BP) response to DOCA than females, and we propose this is due to the relative abundance of Tregs in the female. We have also previously reported that an intact nitric oxide (NO) system is required for Treg maintenance in hypertension, and females have greater NO levels than males. In the current study, we hypothesized that treatment with L‐arginine, a substrate for NO production, would increase renal Tregs and attenuate the sex difference in hypertension in male and female DOCA treated rats. Briefly, male and female Sprague Dawley rats (n=4–6, 10 wks of age) were uni‐nephrectomized and subcutaneously implanted with a DOCA pellet (200 mg/rat, 60‐d time release) and given 0.9% NaCl to drink ad libitum. A subset of rats were treated with L‐arginine (350 mg/kg/d, via drinking water). BP was measured by tail cuff plethysmography at baseline and after 3 wks of DOCA treatment. After 3 wks of treatment, kidneys were processed for flow cytometric analysis of T cells (CD3+CD4+FOXp3+ Tregs, CD3+CD4+RORγ+ Th17 cells, and IL‐10+CD3+ T cells). BP was comparable between treatment groups within each sex at baseline, although males had a higher BP than females (Table, effect of sex, p<0.001, 2‐Way ANOVA). DOCA treatment increased BP in all groups compared to baseline values (Table, effect of DOCA, p=0.002). L‐arginine treatment attenuated DOCA‐induced increases in BP in both sexes, although this effect was greater in females (Table, effect of L‐arginine, p=0.02, interaction of sex and L‐arginine, p=0.03). Females had a more anti‐inflammatory renal T cell profile, with greater levels of Tregs and IL‐10+ cells, whereas males had more pro‐inflammatory Th17 cells (Table, effect of sex, p<0.05 for Tregs, Th17, and IL‐10). Interestingly, despite the significant BP effect observed, L‐arginine treatment did not impact the renal T cell profile in either sex (Table, effect of L‐arg, p>0.05 for Tregs, Th17, and IL‐10). Future studies will examine additional mechanisms by which L‐arginine supplementation lowers BP in both sexes. The DOCA salt model is characterized by high levels of oxidative stress, which is known to impair the NO‐NOS signaling pathway by decreasing the amount of L‐arginine available to produce NO via eNOS.Support or Funding InformationThis work was supported by NIH 5R01HL12709102This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Ablation of Sympathetic Neurons Projecting to Mesenteric Blood Vessels Reduces Splanchnic Nerve Evoked Systemic Blood Pressure Increase: Widespread Projection of Prevertebral Neurons to the Mesenteric Circulation

Celiac ganglionectomy attenuates the increase in arterial pressure (AP) seen in the DOCA‐salt model of hypertension; however, it is unknown which population of splanchnic sympathetic neurons is responsible for the attenuation of DOCA‐salt hypertension. Therefore, we ablated sympathetic post ganglionic neurons specifically innervating mesenteric blood vessels by applying an antibody to dopamine beta hydroxylase conjugated to the neurotoxin saporin (DβH‐Sap) on two, 7 mm segments of mesenteric arteries and veins separated from paravascular nerve trunks. Control animals received IgG‐saporin instead of DβH‐Sap. 3wks after application of saporin conjugates, rats were anesthetized, fitted with a femoral catheter, and the greater splanchnic nerve was dissected. The number of neurons in the celiac ganglia and splanchnic ganglion was considerably less in DβH‐Sap treated animals compared to IgG‐saporin treated control animals. Also, there was nearly complete elimination of TH‐positive perivascular nerve fibers. Stimulation of the greater splanchnic nerve (3Hz, 5v, 1ms for 20s) increased AP in IgG‐sap treated controls (6.2 ± 0.6 mmHg, N=4), while DβH‐Sap treated animals saw a decrease in AP (‐1.5 ± 1.5 mmHg, N=4). Ablation of vascular‐projecting neurons in prevertebral ganglia eliminates the systemic pressor response to splanchnic nerve stimulation. This study also shows that nearly all the vascular‐projecting neurons converge on two, 7 mm segments of mesenteric blood vessels, which suggests that individual prevertebral neurons project widely to the mesenteric circulation.

Abstract 267: Ablation of Sympathetic Neurons Projecting to Mesenteric Blood Vessels Attenuates Nicotine-Induced Rise in Systemic Arterial Pressure

Celiac ganglionectomy attenuates the increase in arterial pressure (AP) seen in the DOCA-salt model of hypertension; however, it is unknown which population of neurons in the celiac ganglion (CG) is responsible for this attenuation. Therefore, we ablated sympathetic post ganglionic neurons selectively innervating mesenteric blood vessels by applying a retrograde tracer, cholera toxin subunit b, conjugated to the neurotoxin saporin (CTB-SAP) on multiple, adjacent branches (~6mm) of mesenteric arteries and veins. Control animals received PBS instead of a CTB-SAP treatment. After 7-10 days rats were anesthetized, and fitted with a femoral catheter to record AP. Nicotine (200mM) was then applied to the surface of the surgically-exposed CG, which caused a significant increase in AP in control animals but not in CTB-SAP treated animals ( Table 1 ). Quantitative morphometry done on the CG revealed a significant reduction in the density of ganglionic neurons in CTB-SAP treated animals when compared to control animals ( Table 1 ). This study shows ablating CG neurons that innervate such a small portion of the mesenteric vasculature reduces the elevation of systemic AP induced by nicotine. Moreover, this study gives way for further investigations into how ablation of neurons innervating mesenteric arteries or veins can modulate AP.

Angiotensin Type 1a Receptors in the Subfornical Organ Are Required for Deoxycorticosterone Acetate-Salt Hypertension

Although elevated renin–angiotensin system activity and angiotensinergic signaling within the brain are required for hypertension, polydipsia, and increased metabolic rate induced by deoxycorticosterone acetate (DOCA)-salt, the contribution of specific receptor subtypes and brain nuclei mediating these responses remains poorly defined. We hypothesized that angiotensin type 1a receptors (AT 1a R) within the subfornical organ (SFO) mediate these responses. Transgenic mice carrying a conditional allele of the endogenous AT 1a R (AT 1a R flox ) were administered an adenovirus encoding Cre-recombinase and enhanced green fluorescent protein (eGFP) or adenovirus encoding eGFP alone into the lateral cerebral ventricle. Adenovirus encoding Cre-recombinase reduced AT 1a R mRNA and induced recombination in AT 1a R flox genomic DNA specifically in the SFO, without significant effect in the paraventricular or arcuate nuclei, and also induced SFO-specific recombination in ROSA TdTomato reporter mice. The effect of SFO-targeted ablation of endogenous AT 1a R was evaluated in AT 1a R flox mice at 3 time points: (1) baseline, (2) 1 week after virus injection but before DOCA-salt, and (3) after 3 weeks of DOCA-salt. DOCA-salt–treated mice with deletion of AT 1a R in SFO exhibited a blunted increase in arterial pressure. Increased sympathetic cardiac modulation and urine copeptin, a marker of vasopressin release, were both significantly reduced in DOCA-salt mice when AT 1a R was deleted in the SFO. Additionally, deletion of AT 1a R in the SFO significantly attenuated the polydipsia, polyuria, and sodium intake in response to DOCA-salt. Together, these data highlight the contribution of AT 1a R in the SFO to arterial pressure regulation potentially through changes on sympathetic cardiac modulation, vasopressin release, and hydromineral balance in the DOCA-salt model of hypertension.

The cardiac expression of Mas receptor is responsive to different physiological and pathological stimuli

The Mas protooncogene encodes a G protein-coupled receptor that has been described as a functional receptor for the cardioprotective fragment of the renin-angiotensin system (RAS), Angiotensin (Ang)-(1-7). The aim of this current study was to evaluate the responsiveness of Mas expression in hearts during different physiological and pathological conditions in rats. Physical training was considered a physiological condition, while isoproterenol-induced hypertrophy, myocardial infarction and DOCA-salt model of hypertension were used as pathological models of heart injury. The expression of Mas was analyzed by western blotting. Although swim-trained rats presented significant cardiac hypertrophy, our physical training protocol was unable to induce changes in the expression of Mas. On the other hand, cardiac hypertrophy and damage elicited by isoproterenol treatment led to a reduction in Mas expression. Myocardial infarction also significantly decreased the expression of Mas after 21 days of myocardial ischemia. Additionally, Mas expression levels were increased in hearts of DOCA-salt rats. Our present data indicate that Mas expression is responsive to different pathological stimuli, thereby suggesting that Mas receptor is involved in the homeostasis of the heart, as well as in the establishment and progression of cardiac diseases.

A custom rat and baboon hypertension gene array to compare experimental models

One challenge in understanding the polygenic disease of hypertension is elucidating the genes involved and defining responses to environmental factors. Many studies focus on animal models of hypertension; however, this does not necessarily extrapolate to humans. Current technology and cost limitations are prohibitive in fully evaluating hypertension within humans. Thus, we have designed a single-array platform that allows direct comparison of genes relevant to hypertension in animal models and non-human primates/human hypertension. The custom array is targeted to 328 genes known to be potentially related to blood pressure control. Studies compared gene expression in the kidney from normotensive rats and baboons. We found 74 genes expressed in both the rat and baboon kidney, 41 genes expressed in the rat kidney that were not detected in the baboon kidney and 34 genes expressed in the baboon kidney that were not detected in the rat kidney. To begin the evaluation of the array in a pathological condition, kidney gene expression was compared between the salt-sensitive deoxycorticosterone acetate (DOCA) rat model of hypertension and sham animals. Gene expression in the renal cortex and medulla from hypertensive DOCA compared with sham rats revealed three genes differentially expressed in the renal cortex: annexin A1 (up-regulated; relative intensity: 1.316 ± 0.321 versus 2.312 ± 0.283), glutamate-cysteine ligase (down-regulated; relative intensity: 3.738 ± 0.174 versus 2.645 ± 0.364) and glutathione-S transferase (down-regulated; relative intensity: 5.572 ± 0.246 versus 4.215 ± 0.411) and 21 genes differentially expressed in the renal medulla. Interestingly, few genes were differentially expressed in the kidney in the DOCA-salt model of hypertension; this may suggest that the complexity of hypertension may be the result of only a few gene-by-environment responsive events.

Activation of the Renal PI3K/Akt/mTOR Signaling Pathway in a DOCA-Salt Model of Hypertension

The present study investigated the changes that occurred in the mammalian target of rapamycin (mTOR) signaling pathway in the kidney as a result of deoxycorticosterone acetate (DOCA)-salt hypertension. Rats were implanted with DOCA strips (200 mg/kg) 1 week after unilateral nephrectomy and were then supplied with 0.9% saline to drink. Four weeks after DOCA implantation, systolic blood pressure (SBP) was measured by use of the tail-cuff method. The expression levels of phosphorylated phosphatidylinositol-3-kinase (PI3K), Akt, and mTOR, as well as the protein expression levels of ED-1 and cyclooxygenase-2 (COX-2), transforming growth factor-β1 (TGF-β1), α-smooth muscle actin (SMA), caspase-3, Bax, and Bcl-2, were then examined in the kidney by semiquantitative immunoblotting. DOCA-salt hypertensive rats were found to have significantly increased SBP as well as an increased kidney weight-to-body weight ratio. Moreover, the phosphorylation of PI3K, Akt, and mTOR was increased in the kidney of DOCA-salt hypertensive rats compared with the control, as was the protein expression of ED-1, COX-2, TGF-β1, and α-SMA. The expression levels of caspase-3 and Bax were increased significantly, whereas Bcl-2 expression was decreased. In conclusion, the phosphorylation of PI3K/Akt/mTOR was increased in the kidney of DOCA-salt hypertensive rats.

Antihypertensive effect of Silymarin on DOCA salt induced hypertension in unilateral nephrectomized rats

The objective of the present investigation was to evaluate the therapeutic efficacy of Silymarin in DOCA salt induced hypertension in unilateral nephrectomized rats. Unilateral nephrectomy was performed in female Wistar rats (150–200 g). A week after unilateral nephrectomy, hypertension was induced by DOCA (25 mg/kg, once a week; s.c; for 4 weeks) dispersed in cottonseed oil. The effect of Silymarin (300 mg/kg and 500 mg/kg, p. o., for 4 weeks) was evaluated in DOCA salt induced hypertensive rats. Systolic blood pressure (BP) was measured once every week during the treatment schedule. After completion of treatment schedule, heart rate, arterial blood pressure and vascular reactivity to various drugs were recorded. Rats from individual group were sacrificed, the heart was dissected out and antioxidant enzyme level SOD, CAT, GSH and TBARS were measured. Urine excretions were measured by flame photometer. Silymarin (300, 500 mg/kg/day, p.o.) significantly (p < 0.05) reduced systolic blood pressure, heart rate, basal arterial blood pressure and pressor responses to NA, Adr, PE and 5-HT in animals treated with DOCA salt as compared with DOCA-salt hypertensive rats. Silymarin significantly increased antioxidant enzyme level of SOD, CAT, GSH, urinary Na+ excretion and decreased TBARS level, urinary K+ excretion compared with DOCA hypertensive group. Silymarin exhibits significant antihypertensive activity in DOCA salt model of hypertension.

Rosuvastatin Attenuates Hypertension-induced Cardiovascular Remodeling Without Affecting Blood Pressure in DOCA-salt Hypertensive Rats

The pleiotropic effects of statins represent potential mechanisms for the treatment of end-organ damage in hypertension. This study has investigated the effects of rosuvastatin in a model of cardiovascular remodeling, the DOCA-salt hypertensive rat. Male Wistar rats weighing 300 to 330 g were uninephrectomized (UNX) or UNX and treated with DOCA (25 mg subcutaneously every fourth day) and 1% NaCl in the drinking water. Compared with UNX controls, DOCA-salt rats developed hypertension, cardiovascular hypertrophy, inflammation with perivascular and interstitial cardiac fibrosis, endothelial dysfunction, and prolongation of ventricular action potential duration at 28 days. Rosuvastatin-treated rats received 20 mg/kg/d of the drug in 10% Tween 20 by oral gavage for 32 days commencing 4 days before uninephrectomy. UNX and DOCA-salt controls received vehicle only. Rosuvastatin therapy attenuated the development of cardiovascular hypertrophy, inflammation, fibrosis, and ventricular action potential prolongation, but did not modify hypertension or vascular dysfunction. We conclude that the pleiotropic effects of rosuvastatin include attenuation of aspects of cardiovascular remodeling in the DOCA-salt model of hypertension in rats without altering systolic blood pressure.

Chronic angiotensin-(1–7) prevents cardiac fibrosis in DOCA-salt model of hypertension

Cardiac remodeling is a hallmark hypertension-induced pathophysiology. In the current study, the role of the angiotensin-(1-7) fragment in modulating cardiac remodeling was examined. Sprague-Dawley rats underwent uninephrectomy surgery and were implanted with a deoxycorticosterone acetate (DOCA) pellet. DOCA animals had their drinking water replaced with 0.9% saline solution. A subgroup of DOCA-salt animals was implanted with osmotic minipumps, which delivered angiotensin-(1-7) chronically (100 ng.kg(-1).min(-1)). Control animals underwent sham surgery and were maintained on normal drinking water. Blood pressure was measured weekly with the use of the tail-cuff method, and after 4 wk of treatment, blood pressure responses to graded doses of angiotensin II were determined by direct carotid artery cannulation. Ventricle size was measured, and cross sections of the heart ventricles were paraffin embedded and stained using Masson's Trichrome to measure interstitial and perivascular collagen deposition and myocyte diameter. DOCA-salt treatment caused significant increases in blood pressure, cardiac hypertrophy, and myocardial and perivascular fibrosis. Angiotensin-(1-7) infusion prevented the collagen deposition effects without any effect on blood pressure or cardiac hypertrophy. These results indicate that angiotensin-(1-7) selectively prevents cardiac fibrosis independent of blood pressure or cardiac hypertrophy in the DOCA-salt model of hypertension.

Attenuation of Cardiovascular Remodeling in DOCA-Salt Rats by the Vasopeptidase Inhibitor, Omapatrilat

Omapatrilat, a vasopeptidase inhibitor, inhibits both neutral endopeptidase and angiotensin-converting enzyme with similar potency. The aim of this study was to investigate whether omapatrilat prevents or reverses cardiovascular remodeling and hypertension in deoxycorticosterone acetate (DOCA)-salt rats. Male Wistar rats (313 ± 2 g, n=114) were uninephrectomized (UNX) with or without further treatment with DOCA and 1% NaCl in the drinking water. Compared with UNX control rats, DOCA-salt rats developed hypertension, cardiovascular hypertrophy, perivascular and interstitial cardiac fibrosis and inflammation, endothelial dysfunction, and the prolongation of ventricular action potential duration within four weeks. The administration of omapatrilat (40 mg/kg/day po) for two weeks commencing two weeks after surgery attenuated the development of cardiovascular hypertrophy, inflammation, fibrosis, and ventricular action potential prolongation. In contrast, omapatrilat treatment did not lower systolic blood pressure nor improve endothelial dysfunction. This study concludes that the renin-angiotensin-aldosterone, natriuretic peptide, and bradykinin systems are directly involved in the pathogenesis of cardiovascular remodeling in the DOCA-salt model of hypertension in rats, which may be independent of their effects on blood pressure.

Comparison of the cardiovascular protection by omapatrilat and lisinopril treatments in DOCA-salt hypertension.

To compare the cardiovascular protection provided by omapatrilat and lisinopril in an experimental model of hypertension. Four-week deoxycorticosterone acetate (DOCA)-salt hypertensive (HT) and age-matched normotensive (NT) rats were treated either with omapatrilat (40 mg/kg per day) or lisinopril (20 mg/kg per day) for 2 weeks before sacrifice, and compared with untreated HT and NT rats sacrificed at ages corresponding to either before or after the drug regimens. Systolic arterial pressure (SAP) of 2 and 4 week HT rats was increased in comparison to age-matched NT rats (P <0.05). Treatment with omapatrilat or lisinopril reduced SAP in HT (P <0.05) similarly by about 10%. Cardiac interstitial collagen, perivascular collagen and media/lumen ratio of coronary arterioles were increased in HT rats. Both treatments partially prevented the rise in perivascular collagen and completely corrected the increased media/lumen ratio in small arterioles from HT (P <0.05). In contrast to NT rats, only a weak coronary dilatation to bradykinin was observed in Langendorff hearts isolated from untreated-HT. This response was slightly improved by lisinopril and markedly improved by omapatrilat (P <0.05). The coronary dilatation to SNP which was reduced in 4-week HT (P <0.05), was partially improved by omapatrilat treatment but not by lisinopril. The enhanced superoxide anion production in aorta from HT rats was partially corrected with omapatrilat and lisinopril. Finally, omapatrilat, unlike lisinopril, markedly reduced mortality in a more severe form of DOCA-salt hypertension. Omapatrilat and lisinopril regressed coronary remodelling and cardiac collagen deposition, and reduced vascular oxidative stress in DOCA-salt hypertensive rats. However, despite similar antihypertensive efficacy, omapatrilat was superior to lisinopril in improving the endothelial-dependent coronary dilatation, suggesting a better vascular protection in the DOCA-salt model of hypertension.

Endothelin antagonist reduces hemodynamic responses to vasopressin in DOCA-salt hypertension.

The contribution of endothelin to the changes in blood pressure, cardiac output, and total peripheral resistance evoked by arginine vasopressin and angiotensin II was investigated in deoxycorticosterone acetate (DOCA)-salt hypertensive rats by infusing the peptides intravenously before and after pretreatment with the endothelin receptor antagonist bosentan. Blood pressure was recorded with radiotelemetry devices and cardiac output was recorded with ultrasonic transit time flow probes in conscious unrestrained animals. The dose-related decreases in cardiac output induced by vasopressin and angiotensin II were unaffected by bosentan. In contrast, the dose-related increases in total peripheral resistance evoked by vasopressin were blunted in both DOCA-salt hypertensive and sham normotensive rats, but this effect of bosentan was greater in the DOCA-salt hypertensive group. In contrast with vasopressin, bosentan failed to change hemodynamic responses to angiotensin II. The exaggerated vascular responsiveness (total peripheral resistance) of the DOCA-salt hypertensive group to vasopressin was largely abolished by bosentan. These results suggest that endothelin contributes to the hemodynamic effects of vasopressin but not angiotensin II in the DOCA-salt model of hypertension.

Total peripheral conductance mediates antihypertensive effect of nonpeptide mixed endothelin receptor antagonist in deoxycorticosterone acetate-salt hypertensive rats

The relative contribution of cardiac output (CO) and total peripheral conductance (TPC) to the changes in blood pressure (BP) evoked by an intravenous injection of bosentan, a nonpeptide mixed endothelin (ET) antagonist, were investigated in conscious unrestrained deoxycorticosterone acetate (DOCA)-salt hypertensive rats and sham-control rats. Blood pressure was recorded by radiotelemetry devices and CO by ultrasonic transit-time flow probes. Bosentan significantly reduced BP (from 141 ± 3 to 111 ± 3 mm Hg) and increased TPC (from 1.19 ± 0.1 to 1.72 ± 0.2 mL/min/kg/mm Hg) in DOCA-salt hypertensive rats, but not in sham rats. An increase in CO opposed the BP-lowering effect of the antagonist. The results demonstrate that the role of ET receptors in the maintenance of the hypertensive state in the DOCA-salt model of hypertension is exerted at the level of the resistance vessels and not on factors that regulate cardiac output.

Hemodynamic effects of a selective endothelin--a receptor antagonist in deoxycorticosterone acetate-salt hypertensive rats.

The time-course changes in blood pressure (BP), cardiac output (CO), and total peripheral conductance (TPC) were investigated during a bolus i.v. infusion of BMS-182874, a selective ETA receptor antagonist, in conscious, unrestrained DOCA-salt hypertensive rats and Sham-operated control rats (SHAM). BP was recorded with radiotelemetry devices and CO with ultrasonic transit-time flow probes. In contrast to vehicle-treated controls, BMS-182874 reduced BP and increased TPC in DOCA-salt hypertensive rats but not in SHAM-rats. A small increase in CO tended to oppose the BP-lowering effect of the antagonist. The results suggest that the role of ETA receptors in the maintenance of the hypertensive state in the DOCA-salt model of hypertension is exerted at the level of the resistance vessels and not on factors that regulate CO.