Animal Model Of Essential Hypertension Research Articles

Proteomics analysis in myocardium of spontaneously hypertensive rats

Hypertension-related left ventricular hypertrophy is recognized as a good predictor of adverse cardiovascular events. However, the underlying mechanism of left ventricular hypertrophy is still not fully understood. This study employed liquid chromatography coupled with tandem mass spectrometry to investigate global changes in protein profile in myocardium of spontaneously hypertensive rat, a classical animal model of essential hypertension. There were 369 differentially expressed proteins in myocardium between spontaneously hypertensive rats and normotensive rats. Xenobiotic catabolic process, cholesterol binding and mitochondrial proton-transporting ATP synthase were found to be the most significantly enriched biological process, molecular function and cellular component terms of Gene Ontology, respectively. Drug metabolism-cytochrome P450 was revealed to be the most significantly enriched Kyoto Encyclopedia of Genes and Genomes pathways. FYN proto-oncogene, Src family tyrosine kinase was found to have the most interactions with other proteins. Differentially expressed proteins involved in xenobiotic catabolic process, lipid transport and metabolism, mitochondrial function might be targets for further study of hypertension-related left ventricular hypertrophy.

PS-B10-5: EFFECTS OF CHRONIC ACETYLCHOLINESTERASE INHIBITION WITH PYRIDOSTIGMINE ON CARDIOVASCULAR SYSTEM AND AUTONOMIC BALANCE IN SPONTANEOUSLY HYPERTENSIVE RATS

Objective: The imbalance in autonomic nervous system, characterized by increased sympathetic and attenuated parasympathetic activity, plays an important role in the pathogenesis of hypertension. The spontaneously hypertensive rats (SHR) which are one of the most studied animal models of essential hypertension, are characterized by autonomic nervous system imbalance. Our study was aimed to determine the effect of chronic inhibition of acetylcholinesterase with pyridostigmine on cardiovascular parameters and sympatho-vagal balance in SHR and Wistar-Kyoto (WKY) rats. Design and method: Adult male SHR and WKY rats were treated with pyridostigmine (25 mg/kg/day) in drinking solution for 2 weeks. The rats were implanted with telemetric transducers to measure blood pressure (BP) and heart rate (HR). Autonomic balance was evaluated by power spectral analysis of systolic blood pressure variability (SBPV) and heart rate variability (HRV). Sympatho-vagal balance was also evaluated pharmacologically by administration of methylatropine (antagonist of muscarinic acetylcholine receptors) and propranolol (antagonist of beta-adrenergic receptors) in a separate set of rats. Results: SHR have elevated BP, increased vascular sympathetic activity (low frequency component of SBPV), and reduced HRV compared to WKY. Pyridostigmine significantly reduced HR in rats of both strains (during both dark and light phase) and BP during the dark (active) phase compared to untreated controls. Acetylcholinesterase activity in plasma was significantly reduced by pyridostigmine treatment in both strains (SHR 53 ± 3%, WKY 46 ± 3%). Sympatho-vagal balance examination revealed reduced cardiac vagal tone in SHR as evidenced by blunted HR response to the muscarinic receptor blocker methylatropine and increased cardiac sympathetic tone as evidenced by elevated HR response to the beta-blocker propranolol. Pyridostigmine treatment increased cardiac vagal tone and decreased cardiac sympathetic tone in SHR to the levels of untreated WKY. Moreover, pyridostigmine increased HRV and reduced low frequency component of SBPV in SHR indicating the restoration of autonomic balance. The reduction of sympathetic tone in pyridostigmine-treated rats was also evident from the reduction of plasma levels of noradrenaline. The potentiation of cardiac parasympathetic activity by pyridostigmine treatment was confirmed by the attenuation of restraint stress-induced tachycardia in both strains. Conclusions: Chronic stimulation of peripheral cholinergic system with pyridostigmine leads to the improvement of autonomic nervous system balance in SHR by increasing cardiac vagal tone and reducing sympathetic tone. Thus, chronic treatment with acetylcholinesterase inhibitors seems to be a promising therapeutic strategy for the restoration of autonomic balance in cardiovascular diseases.

THE DESIGNING EXPERIMENT OF ESSENTIAL HYPERTENSION: THE CHOICE OF A CONTROL GROUP FOR SPONTANEOUSLY HYPERTENSIVE RATS

Objective: The spontaneously hypertensive rat (SHR) is the most widely studied animal model of essential hypertension. The Wistar-Kyoto rats (WKY) were originally bred as normotensive controls for the SHR, while the Wistar (WIS) strain is generally the most popular in research. The objective of the study was to check whether Wistar could be used as controls for SHR by comparing blood pressure levels in three groups of animals. Design and method: Adult male WIS (n = 5), WKY (n = 6), and SH (n = 4) rats, 20th week of age, were used. The animals were housed in the Animal Research Center of the Lithuanian University of Health Sciences under permission No. G2–137. They were kept in collective cages and allocated in a controlled environment with a light/dark cycle (12/12 h), the temperature at 22 ± 2C, and had free access to food and water. Following animal sedation, heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were measured using the on-invasive method of tail-cuff (AD Instruments IN125/R NIBP system, UK and LabChart software). Each measurement was performed ten times, and the median value was used. All measurements were performed by the same researcher in a quiet environment. Mean arterial pressure (MAP) was calculated by the following equation: DBP+1/3(SBP-DBP). The Kruskal-Wallis test was used to determine group differences. The Mann-Whitney test was used for two groups comparisons. Results: SHR BP values were highest, WKY - in the middle, and WIS - the lowest. Measured parameters differed statistically significantly between the three rat groups (p < 0.05) (Table 1). The two groups comparison revealed that all parameters in SHR had statistically significant differences between the WKY as well as WIS (p < 0.05), except HR in WIS. HR did not differ between SHR and WIS rats (p = 0.190). Comparing WKY and WIS groups, there was no significant difference between SBP (p = 0.284), DBP (p = 0.524), MAP (p = 0.354), except HR, which was significantly higher in WIS (p = 0.002). Conclusions: Adult spontaneously hypertensive rats have significant arterial hypertension. Blood pressure measurements of Wistar-Kyoto and Wistar rats do not differ, so both of them can be used as controls for hypertensive rats.

In vivo symmetric multi-contrast MRI brain templates and atlas for spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHRs) are a valuable animal model of essential hypertension. The increasing use of SHRs in neuroimaging has generated an urgent demand for a template set that provides a reference for advanced data analysis. Structural T2-weighted magnetic resonance imaging (MRI), diffusion tensor imaging (DTI) and functional MRI scans that were used to build the template set were obtained from 8 SHRs longitudinally scanned in vivo at 10, 24 and 52weeks of age. These symmetric multi-contrast templates were constructed by iterative registration and averaging. The cortical atlas was derived from the Tohoku atlas, and the subcortical regions were manually delineated based on the templates. A set of SHR brain images named the Hebei Medical University rat brain template set (HRT) comprised 3D symmetric T2WI, raw T2-weighted signal with no added diffusion weighting (B0), fractional anisotropy (FA), mean diffusivity (MD) and blood oxygen level-dependent (BOLD) templates; tissue probability maps (TPMs) of gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF); and a whole-brain atlas with 163 labels. We quantitatively validated the template and characterized the longitudinal changes in brain morphology in different brain tissues as SHRs aged. To our knowledge, the HRT is the first MRI template set for SHRs. We believe that the HRT can serve as a beneficial tool for precise analysis of the SHR brain using structural and functional MRI, which can promote neuroimaging studies on essential hypertension.

Examining the role of extacellular vesicles in blood pressure regulation

Extracellular vesicles (EVs) are membrane-enclosed structures that aid in intercellular communication and other biological processes. Recent studies implicate EVs in various acute and chronic disease states, including hypertension. We have previously demonstrated that the gut microbiota plays a causal role in the pathogenesis of hypertension. However, the mechanisms by which the microbiota influences host blood pressure are largely unknown. We hypothesized that EVs act as mediators between the gut microbiota and host, exerting bidirectional effects to regulate blood pressure. For our experiments, we used the spontaneously hypertensive stroke prone rat (SHRSP), a well-known animal model of essential hypertension, and its corresponding normotensive control, the Wistar-Kyoto rat (WKY). To demonstrate the impact of EVs on host blood pressure, we transplanted plasma EVs from SHRSP and WKY donors into SHRSP and WKY recipients via intravenous injection. Treatment duration was 4 weeks, during which systolic blood pressure (SBP) measurements were taken. In SHRSP, WKY-EVs had a statistically significant SBP lowering effect over time compared with SHRSP-EVs (p=0.03), with a reduction of SBP of 23 mmHg at 4 weeks (166 ± 1 vs. 189 ± 3 mmHg; p=0.05). In WKYs, EV type had a significant main effect on SBP (p=0.05), with those receiving SHRSP-EVs exhibiting elevated SBP. We then performed flow cytometry analysis on various tissues from the treatment groups to investigate if immune and inflammatory processes could underlie EV action. We found that SHRSP that received SHRSP-EVs (SHRSP control) had increased Th17 cells (p<0.0001) and decreased regulatory T (Treg) cells (p<0.05) in ileum compared to WKY that received WKY-EVs (WKY control). These results are consistent with previous reports citing Th17/Treg imbalance toward Th17 dominance as a critical factor in hypertension. Interestingly, WKY-EV treatment in SHR restored Th17/Treg balance, decreasing Th17 numbers in brain (p<0.0001), ileum (p<0.0001) and cecum (p<0.01) and increasing Treg numbers in ileum (p<0.001) compared to SHRSP control. Conversely, WKY that received SHR-EVs had fewer Tregs in ileum (p<0.05) compared to WKY control, demonstrating that SHRSP-EV treatment in WKY resulted in deleterious inflammatory effects on gut. Finally, to examine if the effects of EVs on SBP may be mediated through alteration of the gut microbiota, we administered SHRSP-EVs or WKY-EVs to germ free rats lacking a gut microbiota. Germ free rats receiving SHRSP-EVs exhibited significantly elevated SBP as compared to those receiving WKY-EVs (150 ± 5 vs. 129 ± 4 mmHg; p=0.01). This finding further demonstrates the SBP elevating effect of SHRSP-EVs, and suggests EV alteration of the gut microbiota is not required to influence host blood pressure. Future studies will seek to establish how microbiota may alter circulating EV profile and function to promote the pathogenesis of hypertension. Overall, our data suggest that EVs play an important role in regulation of host blood pressure and gut inflammation, in part by alteration of the Th17/Treg balance.

Abstract MP32: Effectiveness Of Investigational RNAi Therapeutics Targeting Liver Angiotensinogen In Experimental Chronic Kidney Disease

Background: RNAi therapeutics targeting angiotensinogen (AGT) lower blood pressure in animal models of essential hypertension, but whether this treatment is beneficial in hypertensive chronic kidney disease (CKD) is yet unknown. Our aim was to assess the effectiveness of a small interfering RNA (siRNA) targeting hepatic AGT in a rat model of hypertensive CKD. Methods: Sprague Dawley rats (n=7-12 per group) were subjected to 5/6th nephrectomy, allowed to recover for four weeks, and subsequently subjected to one of five treatments: (1) vehicle, (2) AGT siRNA (10-30 mg/kg, s.c. every 2 weeks), (3) AGT siRNA + losartan (30 mg/kg/d), (4) losartan (30 mg/kg/d), or (5) losartan + captopril (30 and 6 mg/kg/d). Mean arterial pressure (MAP) was measured by radiotelemetry for 4 weeks, glomerular filtration rate (GFR) was measured by transcutaneous FITC-sinistrin clearance. Results: AGT siRNA and AGT siRNA + losartan reduced plasma AGT by 96.5 ± 1.4% and 97.0 ± 2.3%, respectively. Over the course of 4 weeks, proteinuria increased with vehicle and this increase was abrogated by all treatments (Δ proteinuria at 4 weeks versus baseline: +0.17 [0.12, 0.23], +0.02 [-0.04, 0.05], -0.01 [-0.07, 0.06], -0.05 [-0.12, 0.00], -0.01 [-0.06, 0.11] for vehicle, AGT siRNA, AGT siRNA + losartan, losartan, losartan + captopril, P &lt; 0.05 for all groups compared with vehicle). Similarly, heart weight was equally reduced by all treatments except vehicle. No intervention affected GFR. Over the course of 4 weeks, MAP increased (from a baseline of 154 ± 18 mmHg) during vehicle treatment and this rise was prevented by AGT siRNA (+13 ± 15 mmHg vs. -2 ± 14 mmHg, P &gt; 0.05 for difference between groups). Combination treatment with AGT siRNA + losartan, losartan + captopril, and losartan alone caused a similar and marked reduction in MAP (-17 ± 14 mmHg, -21 ± 17 mmHg, and -33 ± 20 mmHg, P &lt; 0.05 versus vehicle for all; differences between groups not significant). Conclusion: In experimental CKD, AGT siRNA monotherapy appears to reduce proteinuria and heart weight in a blood pressure-independent fashion, to a similar degree as losartan or combination treatment. Thus, an siRNA targeting hepatic AGT may be a potential therapeutic approach for providing renal and cardioprotection in CKD.

Zamicastat is a noncompetitive Dopamine‐β‐hydroxylase inhibitor that modulates sympathetic nervous system activity

Dopamine‐β‐hydroxylase (DβH; EC 1.14.17.1) is an enzyme responsible for the conversion of dopamine (DA) into norepinephrine (NE). It is present in the chromaffin cells of adrenal medulla and in noradrenergic nerve terminals of the central and peripheral sympathetic nervous system. DβH inhibition has been proposed as an alternative mechanism for the treatment of hypertension and chronic heart failure. Zamicastat ((R)‐5‐(2‐(benzylamino)ethyl)‐1‐(6,8‐difluorochroman‐3‐yl)‐1H‐imidazole‐2(3H)‐thione) is a novel DβH inhibitor. The aim of this study was to characterize the pharmacodynamics of Zamicastat in vivo, both in Wistar Han and in spontaneously hypertensive rats (SHR), and on DβH in human cells. DβH activity was measured by a modification of the Nagatsu and Udenfriend (1) spectrophotometric method, based on the conversion of tyramine into octopamine either in adrenal tissues of rats administered orally with Zamicastat (30 mg/Kg) or vehicle, or in human neuroblastoma (SK‐N‐SH) cells. Zamicastat pharmacodynamic characterization in vivo was performed in Wistar rats by evaluating NE and DA levels in tissues using HPLC with electrochemical detection at 9h post‐administration. Additionally, systolic and diastolic blood pressure, heart rate and activity were measured continually by telemetry in SHR rats (a model of essential hypertension) and their controls, Wistar Kyoto (WKY). Zamicastat was found to be a reversible noncompetitive inhibitor of DβH towards tyramine, with a Ki value of 43 (21; 66) nM and either noncompetitive or uncompetitive towards ascorbic acid. Zamicastat (30 mg/Kg, p.o.) fully inhibits adrenal DβH activity from 2 to 8h recovering to baseline values after 24h. This is accompanied with a decrease in NE and an increase in DA in peripheral tissues, namely left ventricle and kidney but not significantly in the central nervous system (brain stem or prefrontal‐cortex). Zamicastat at 3, 30 and 100 mg/Kg displayed a dose‐dependent decrease on systolic and diastolic blood pressure with no effect in heart rate or overall activity when evaluated in SHR rats by telemetry. In conclusion, Zamicastat is a DβH inhibitor displaying binding affinity for both the free enzyme and the complex enzyme‐substrate, that when orally administered at 30 mg/Kg to rats acts peripherally and significantly reduces sympathetic activity by decreasing NE levels and consequently systolic and diastolic blood pressure in an animal model of essential hypertension.

Stimulation of brain cannabinoid CB1 receptors can ameliorate hypertension in spontaneously hypertensive rats.

Excessive activation of the sympatho-adrenomedullary system plays a pathogenic role in triggering and sustaining essential hypertension. We previously reported that, in normotensive rats, intracerebroventricularly (i.c.v.) administered neuropeptides, corticotropin-releasing factor and bombesin induced activation of the sympatho-adrenomedullary system, and that brain cannabinoid CB1 receptors negatively regulated this activation. In this study, we investigated the effects of brain CB1 receptor stimulation on blood pressure and the sympatho-adrenomedullary outflow in spontaneously hypertensive rats (SHRs), commonly used animal models of essential hypertension, and in Wistar-Kyoto (WKY) rats, normotensive controls of SHRs. In 18-week-old SHRs and WKY rats under urethane anaesthesia (1.0g/kg, i.p.), SHRs exhibited significantly higher systolic, mean and diastolic blood pressures and plasma noradrenaline and adrenaline, and a lower heart rate than WKY rats. Single administration of arachidonyl 2'-chloroethylamide (ACEA, CB1 agonist, 1.4µmol/animal, i.c.v.) significantly but partially reduced mean and diastolic blood pressures and the plasma level of noradrenaline in SHRs compared to vehicle (N,N-dimethylformamide)-treated SHRs. These ACEA-induced reductions were abolished by central pretreatment with rimonabant (CB1 antagonist, 300nmol/animal, i.c.v.), which alone showed no significant effect on blood pressures or plasma noradrenaline and adrenaline levels of SHRs. On the other hand, ACEA had no significant effect on blood pressure or plasma noradrenaline and adrenaline levels in WKY rats. These results suggest that stimulation of brain CB1 receptors can ameliorate hypertension accompanied by enhanced sympathetic outflow without affecting blood pressure under normotensive conditions.

Trans-3,5-dicaffeoylquinic acid from Geigeria alata Benth. & Hook.f. ex Oliv. & Hiern with beneficial effects on experimental diabetes in animal model of essential hypertension

Geigeria alata Benth. & Hook.f. ex Oliv. & Hiern (Asteraceae) is used in Sudanese folk medicine for treatment of diabetes. The study aimed to estimate the acute oral toxicity of trans-3,5-dicaffeoylquinic acid (3,5-diCQA) from G. alata roots and to assess its antihypeglycemic, antioxidant and antihypertensive effects on chemically-induced diabetic spontaneously hypertensive rats (SHRs). The structure of 3,5-diCQA was established by NMR and HRMS spectra. Type 2 diabetes was induced by intraperitoneal injection of streptozotocin. 3,5-diCQA was slightly toxic with LD50 = 2154 mg/kg. At 5 mg/kg 3,5-diCQA reduced significantly (p < 0.05) the blood glucose levels by 42%, decreased the blood pressure by 22% and ameliorated the oxidative stress biomarkers reduced glutathione, malondialdehyde, and serum biochemical parameters. The beneficial effect on antioxidant enzymes was evidenced by the elevated glutathione peroxidase, glutathione reductase, and glutathione S-transferase activitiy in the livers of diabetic animals. 3,5-diCQA prevents the histopathological changes related to diabetes and hypertension. 3,5-diCQA was more potent α-glucosidase inhibitor (IC50 27.24 μg/mL) than acarbose (IC50 99.77 μg/mL). The antihyperglycemic action of the compound was attributed to the α-glucosidase inhibition. The beneficial effects of 3,5-diCQA on streptozotocin-induced diabetic hypertensive rats support the traditional use of G.alata for the management of diabetes.

Consequences of low-intensity light at night on cardiovascular and metabolic parameters in spontaneously hypertensive rats 1.

Circadian rhythms are an inherent property of physiological processes and can be disturbed by irregular environmental cycles, including artificial light at night (ALAN). Circadian disruption may contribute to many pathologies, such as hypertension, obesity, and type 2 diabetes, but the underlying mechanisms are not understood. Our study investigated the consequences of ALAN on cardiovascular and metabolic parameters in spontaneously hypertensive rats, which represent an animal model of essential hypertension and insulin resistance. Adult males were exposed to a 12 h light - 12 h dark cycle and the ALAN group experienced dim light at night (1-2 lx), either for 2 or 5 weeks. Rats on ALAN showed a loss of light-dark variability for systolic blood pressure, but not for heart rate. Moreover, a gradual increase of systolic blood pressure was recorded over 5 weeks of ALAN. Exposure to ALAN increased plasma insulin and hepatic triglyceride levels. An increased expression of metabolic transcription factors, Pparα and Pparγ, in the epididymal fat and a decreased expression of Glut4 in the heart was found in the ALAN group. Our results demonstrate that low-intensity ALAN can disturb blood pressure control and augment insulin resistance in spontaneously hypertensive rats, and may represent a serious risk factor for cardiometabolic diseases.

Increased arterial pressure in mice with overexpression of the ADHD candidate gene calcyon in forebrain.

The link between blood pressure (BP) and cerebral function is well established. However, it is not clear whether a common mechanism could underlie the relationship between elevated BP and cognitive deficits. The expression of calcyon, a gene abundant in catecholaminergic and hypothalamic nuclei along with other forebrain regions, is increased in the brain of the spontaneously hypertensive rat (SHR) which is a widely accepted animal model of essential hypertension and attention deficit hyperactivity disorder (ADHD). Previous studies demonstrated that mice with up-regulation of calcyon in forebrain (CalOE) exhibit deficits in working memory. To date, there is no evidence directly connecting calcyon to BP regulation. Here, we investigated whether forebrain up-regulation of calcyon alters BP using radiotelemetry. We found that CalOE mice exhibited higher mean arterial pressure (MAP) compared to tTA controls. Plasma norepinephrine levels were significantly higher in CalOE mice compared to tTA controls. Silencing the transgene with doxycycline normalized BP in CalOE mice, whereas challenging the mice with 4% high salt diet for 12 days exacerbated the MAP differences between CalOE and tTA mice. High salt diet challenge also increased proteinuria and urinary thiobarbituric acid reactive substances (TBARs) in tTA and CalOE; and the increases were more prominent in CalOE mice. Taken together, our data suggest that upregulation of calcyon in forebrain could increase BP via alterations in noradrenergic transmission and increased oxidative stress during high salt challenge. Overall, this study reveals that calcyon could be a novel neural regulator of BP raising the possibility that it could play a role in the development of vascular abnormalities.

Gallic Acid Reduces Blood Pressure and Attenuates Oxidative Stress and Cardiac Hypertrophy in Spontaneously Hypertensive Rats

Gallic acid (GA) has been reported to have beneficial effects on cancer, vascular calcification, and diabetes-induced myocardial dysfunction. We hypothesized that GA controls hypertension via oxidative stress response regulation in an animal model for essential hypertension. Spontaneously hypertensive rats (SHRs) were administered GA for 16 weeks. GA treatment lowered elevated systolic blood pressure in SHRs through the inhibition of vascular contractility and components of the renin-angiotensin II system. In addition, GA administration reduced aortic wall thickness and body weight in SHRs. In SHRs, GA attenuated left ventricular hypertrophy and reduced the expression of cardiac-specific transcription factors. NADPH oxidase 2 (Nox2) and GATA4 mRNA expression was induced in SHR hearts and angiotensin II-treated H9c2 cells; this expression was downregulated by GA treatment. Nox2 promoter activity was increased by the synergistic action of GATA4 and Nkx2-5. GA seems to regulate oxidative stress by inhibiting the DNA binding activity of GATA4 in the rat Nox2 promoter. GA reduced the GATA4-induced Nox activity in SHRs and angiotensin II-treated H9c2 cells. GA administration reduced the elevation of malondialdehyde levels in heart tissue obtained from SHRs. These findings suggest that GA is a potential therapeutic agent for treating cardiac hypertrophy and oxidative stress in SHRs.

Effects of transgenic expression of dopamine beta hydroxylase (Dbh) gene on blood pressure in spontaneously hypertensive rats.

The spontaneously hypertensive rat (SHR) is the most widely used animal model of essential hypertension and left ventricular hypertrophy. Catecholamines play an important role in the pathogenesis of both essential hypertension in humans and in the SHR. Recently, we obtained evidence that the SHR harbors a variant in the gene for dopamine beta hydroxylase (Dbh) that is associated with reduced adrenal expression of Dbh mRNA and reduced DBH enzymatic activity which correlated negatively with blood pressure. In the current study, we used a transgenic experiment to test the hypothesis that reduced Dbh expression predisposes the SHR to hypertension and that augmentation of Dbh expression would reduce blood pressure. We derived 2 new transgenic SHR-Dbh lines expressing Dbh cDNA under control of the Brown Norway (BN) wild type promoter. We found modestly increased adrenal expression of Dbh in transgenic rats versus SHR non-transgenic controls that was associated with reduced adrenal levels of dopamine and increased plasma levels of norepinephrine and epinephrine. The observed changes in catecholamine metabolism were associated with increased blood pressure and left ventricular mass in both transgenic lines. We did not observe any consistent changes in brainstem levels of catecholamines or of mRNA levels of Dbh in the transgenic strains. Contrary to our initial expections, these findings are consistent with the possibility that genetically determined decreases in adrenal expression and activity of DBH do not represent primary determinants of increased blood pressure in the SHR model.

Beneficial effects of simulated gastro-intestinal digests of fried egg and its fractions on blood pressure, plasma lipids and oxidative stress in spontaneously hypertensive rats.

BackgroundWe have previously characterized several antihypertensive peptides in simulated digests of cooked eggs and showed blood pressure lowering property of fried whole egg digest. However, the long-term effects of this hydrolysate and its fractions on blood pressure are not known. Therefore, the objectives of the study were to determine the effects of long term administration of fried whole egg hydrolysate and its fractions (i.e. egg white and egg yolk) on regulation of blood pressure and associated factors in cardiovascular disease such as plasma lipid profile and tissue oxidative stress.Methods and ResultsWe used spontaneously hypertensive rats (SHR), an animal model of essential hypertension. Hydrolysates of fried egg and its fractions were prepared by simulated gastro-intestinal digestion with pepsin and pancreatin. 16–17 week old male SHRs were orally administered fried whole egg hydrolysate, non-hydrolyzed fried whole egg, egg white hydrolysate or egg yolk hydrolysates (either defatted, or not) daily for 18 days. Blood pressure (BP) and heart rate were monitored by telemetry. Animals were sacrificed at the end of the treatment for vascular function studies and evaluating plasma lipid profile and tissue oxidative stress. BP was reduced by feeding fried whole egg hydrolysate but not by the non-hydrolyzed product suggesting a critical role for in vitro digestion in releasing anti-hypertensive peptides. Egg white hydrolysate and defatted egg yolk hydrolysate (but not egg yolk hydrolysate) also had similar effects. Reduction in BP was accompanied by the restoration of nitric oxide (NO) dependent vasorelaxation and reduction of plasma angiotensin II. Fried whole egg hydrolysate also reduced plasma levels of triglyceride although it was increased by the non-hydrolyzed sample. Additionally the hydrolyzed preparations attenuated tissue oxidative stress.ConclusionOur results demonstrate that fried egg hydrolysates exert anti-hypertensive effects, improve plasma lipid profile and attenuate tissue oxidative stress in vivo.

Recent Progress in the Genetics of Spontaneously Hypertensive Rats

The spontaneously hypertensive rat (SHR) is the most widely used animal model of essential hypertension and accompanying metabolic disturbances. Recent advances in sequencing of genomes of BN-Lx and SHR progenitors of the BXH/HXB recombinant inbred (RI) strains as well as accumulation of multiple data sets of intermediary phenotypes in the RI strains, including mRNA and microRNA abundance, quantitative metabolomics, proteomics, methylomics or histone modifications, will make it possible to systematically search for genetic variants involved in regulation of gene expression and in the etiology of complex pathophysiological traits. New advances in manipulation of the rat genome, including efficient transgenesis and gene targeting, will enable in vivo functional analyses of selected candidate genes to identify QTL at the molecular level or to provide insight into mechanisms whereby targeted genes affect pathophysiological traits in the SHR.

Abstract 287: Radiofrequency Renal Nerve Ablation Attenuates Hypertension in Spontaneously Hypertensive Rats (SHR)

Radiofrequency catheter ablation (RF-ABL) of the renal arteries decreases blood pressure in patients with drug-resistant hypertension. This study investigated whether RF-ABL of the renal arteries alters blood pressure (BP) in an animal model of essential hypertension, the spontaneously hypertensive rat (SHR). Methods Nineteen-week old male SHR were instrumented with radio-telemetry probes for chronic measurement of BP (Systolic, SBP; Diastolic, DBP). After 1-week, control BP was measured in rats for 3 days. The next day SHR were anesthetized and randomly received either bilateral Sham-ABL (n=5) or RF-ABL (n=6) of the renal arteries (Biosense Webster Stockert 70 generator and RF-probe). The tip of the RF-probe was applied externally to a small dissected segment of each renal artery and stimulated circumferentially (10 Watts). BP was then measured three times a week for 8 weeks. Results In anesthetized hypertensive SHR, RF-ABL of a single renal artery did not alter BP. In contrast, subsequent RF-ABL of the contralateral renal artery produced an immediate (&lt;15 seconds) decrease in mean arterial blood pressure (MAP, range Δ -60 to -100 mmHg). BP in hypertensive SHR was not altered during or after the Sham-RF procedure. In conscious SHR, BP was significantly decreased the day after RF-ABL (153±8/102±4 mmHg) and throughout the post-ABL study (4-week SBP/DBP, 173±7/120±5; 8-weeks, 171±6/116±4 mmHg) compared to pre-ABL control levels (SBP/DBP, 187±9/130±5 mmHg). At the end of week-1 the peak increase in MAP to cage switch stress was significantly blunted and the time to return to basal BP was shortened in RF-ABL (peak Δ 18±5 mmHg; 30-min to basal) vs. Sham-ABL (peak Δ 32±3 mmHg; 70-min to basal). At the end of week-8, the hypotensive response to i.p. chlorisondamine was blunted in RF-ABL (Δ -39±4 mmHg) vs. Sham-ABL rats (Δ -53±2 mmHg). Conclusions These data demonstrate that in hypertensive SHR, bilateral RF-ABL of the renal arteries produces, presumably via blockade of renal sympathetic afferent/efferent neural pathways, a reduction in BP, which by 4-weeks is reset to a lower basal level. These findings indicate that RF-ABL can be used in rodents to investigate the therapeutic mechanisms by which endovascular renal denervation reduces blood pressure in hypertension.

Abstract 432: Up-regulation of Calcyon Increases Arterial Pressure via Enhancement of Adrenergic Transmission

Recent studies suggest a link between blood pressure (BP) and executive functions including working memory, response inhibition, and attention. Older adults and children with hypertension exhibit deficits in working memory and attention; however, it is not clear whether a common mechanism could link the elevation in BP and the cognitive abnormalities. The expression of the Calcyon (Caly), a protein which regulates receptor endocytosis, is increased in the brain of the spontaneously hypertensive rat (SHR), a widely accepted animal model of essential hypertension and attention deficit hyperactivity disorder. We hypothesize that Caly up-regulation in forebrain elevates BP under normal physiological response by altering adrenergic transmission. Radio-telemetry transmitters were implanted in CalOE transgenic mice in which Caly is up-regulated, and in tTA littermate controls. Mean arterial pressure was significantly higher in CalOE mice compared to tTA control (121± 1 vs. 108±1 mmHg, P&lt;0.05). Consistent with deficits in executive functions, CalOE mice were also more active and less able to extinguish a learned behavior than tTA controls. Silencing the transgene with doxycycline treatment improved learning deficits and prevented the elevation in BP in CalOE mice. Plasma nor-epinephrine levels were higher in CalOE vs. tTA control mice (20±2 vs. 13±4 ng/ml). In the brain, dopamine levels were significantly lower in CalOE mice vs. control (0.2 ± 0.02 vs. 0.5±0.08 ng/mg) together with decreased dopamine D1 receptor expression whereas urinary dopamine excretion levels were higher in CalOE vs. control (0.5± 0.1 vs. 0.1± .04 μg/day, P&lt;0.05). These data suggest that up-regulation of Caly in brain could increase BP and compromise inhibitory control mechanisms under normal physiological condition via the differential regulation of adrenergic transmission.

Casein Kinase 2-mediated Synaptic GluN2A Up-regulation Increases N-Methyl-d-aspartate Receptor Activity and Excitability of Hypothalamic Neurons in Hypertension

Increased glutamatergic input, particularly N-methyl-D-aspartate receptor (NMDAR) activity, in the paraventricular nucleus (PVN) of the hypothalamus is closely associated with high sympathetic outflow in essential hypertension. The molecular mechanisms underlying augmented NMDAR activity in hypertension are unclear. GluN2 subunit composition at the synaptic site critically determines NMDAR functional properties. Here, we found that evoked NMDAR-excitatory postsynaptic currents (EPSCs) of retrogradely labeled spinally projecting PVN neurons displayed a larger amplitude and shorter decay time in spontaneously hypertensive rats (SHRs) than in Wistar-Kyoto (WKY) rats. Blocking GluN2B caused a smaller decrease in NMDAR-EPSCs of PVN neurons in SHRs than in WKY rats. In contrast, GluN2A blockade resulted in a larger reduction in evoked NMDAR-EPSCs and puff NMDA-elicited currents of PVN neurons in SHRs than in WKY rats. Blocking presynaptic GluN2A, but not GluN2B, significantly reduced the frequency of miniature EPSCs and the firing activity of PVN neurons in SHRs. The mRNA and total protein levels of GluN2A and GluN2B in the PVN were greater in SHRs than in WKY rats. Furthermore, the GluN2B Ser(1480) phosphorylation level and the synaptosomal GluN2A protein level in the PVN were significantly higher in SHRs than in WKY rats. Inhibition of protein kinase CK2 normalized the GluN2B Ser(1480) phosphorylation level and the contribution of GluN2A to NMDAR-EPSCs and miniature EPSCs of PVN neurons in SHRs. Collectively, our findings suggest that CK2-mediated GluN2B phosphorylation contributes to increased synaptic GluN2A, which potentiates pre- and postsynaptic NMDAR activity and the excitability of PVN presympathetic neurons in hypertension.

Exercise in hypertension: do skeletal muscle reflexes make this a dangerous proposition?

the benefits of exercise and exercise training are numerous, varying from increasing skeletal muscle strength to enhancing cardiovascular and respiratory fitness. These attributes of exercise are key elements to the maintenance of good health and the improvement of athletic performance. But are

Stress-induced changes in c-Fos and corticotropin releasing hormone immunoreactivity in the amygdala of the spontaneously hypertensive rat

The present study was undertaken to test the hypothesis that dysregulation of the amygdala contributes to the exaggerated autonomic response to stress in an animal model of essential hypertension. Spontaneously hypertensive (SHR) and normotensive Wistar male rats were chronically instrumented and exposed to 20 min of either air jet stress (AJS) or air noise alone (CON). AJS induced a significant increase in both heart rate and arterial pressure that was greater in the SHR. AJS induced a significant increase in c-Fos-like immunoreactivity (FLI) throughout the caudal-rostral extent of the basolateral, medial, and central (CEA) subnuclei of the amygdala. Differences in FLI between strains were localized to the rostral CEA and the SHR expressed significantly less FLI. AJS also induced a significant increase in the number of corticotrophin releasing hormone (CRH) positive neurons in the CEA. Differences between strains were localized to the caudal CEA and the number of CRH-positive cells was significantly greater in the SHR. The stress-induced increase in CRH labeling in caudal CEA of the SHR was coupled to a greater increase in FLI in the rostral locus coeruleus (LC) of the SHR versus the Wistar. AJS also induced significant increases in FLI in several hypothalamus subnuclei, but no strain-related differences were identified. These results suggest for the first time that dysregulation of CRH-positive cells in the caudal CEA and reduced excitation and/or exaggerated inhibition of rostral CEA neurons may contribute to the exaggerated cardiovascular response to stress in the SHR, possibly through descending modulation of the rostral LC.