Blood Pressure In Normotensive Rats Research Articles

Novel Arylpiperazine Derivatives of Salicylamide with α1-Adrenolytic Properties Showed Antiarrhythmic and Hypotensive Properties in Rats.

Cardiovascular diseases remain one of the leading causes of death worldwide. Unfortunately, the available pharmacotherapeutic options have limited effectiveness. Therefore, developing new drug candidates remains very important. We selected six novel arylpiperazine alkyl derivatives of salicylamide to investigate their cardiovascular effects. Having in mind the beneficial role of α1-adrenergic receptors in restoring sinus rhythm and regulating blood pressure, first, using radioligand binding assays, we evaluated the affinity of the tested compounds for α-adrenergic receptors. Our experiments revealed their high to moderate affinity for α1- but not α2-adrenoceptors. Next, we aimed to determine the antiarrhythmic potential of novel derivatives in rat models of arrhythmia induced by adrenaline, calcium chloride, or aconitine. All compounds showed potent prophylactic antiarrhythmic activity in the adrenaline-induced arrhythmia model and no effects in calcium chloride- or aconitine-induced arrhythmias. Moreover, the tested compounds demonstrated therapeutic antiarrhythmic activity, restoring a normal sinus rhythm immediately after the administration of the arrhythmogen adrenaline. Notably, none of the tested derivatives affected the normal electrocardiogram (ECG) parameters in rodents, which excludes their proarrhythmic potential. Finally, all tested compounds decreased blood pressure in normotensive rats and reversed the pressor response to methoxamine, suggesting that their hypotensive mechanism of action is connected with the blockade of α1-adrenoceptors. Our results confirm the antiarrhythmic and hypotensive activities of novel arylpiperazine derivatives and encourage their further investigation as model structures for potential drugs.

Abstract 034: Absence Of Tachyphylaxis And Vasorelaxant Effect Induced By Nono2p, A New Nitric Oxide Donor

Introduction: Decreased bioavailability of nitric oxide (NO) plays a mechanistic role in hypertension and myocardial infarction. NO donors are potent vasodilators, but often exhibit toxicity or vascular tolerance. The aim of this study was to investigate the vascular activity possible tachyphylaxis of NONO2P, a novel NO donor. Methods: Male Wistar rats were euthanized, and the superior mesenteric artery was isolated for recordings of isometric force, and in vivo experiments were performed to evaluate blood pressure in non-anesthetized normotensive rats. Results: Cumulative administration of the NONO2P (10 -13 to 3x10 -6 M) induced endothelium-independent relaxation (Emax:111.51 ± 2.31%; pD2: 8.51 ± 0.08, n=9) in arterial rings pre-contracted with phenylephrine (Phe,1μM). However, the relaxation was reduced in pre-contracted rings with Phe exposed to Tyrode's solution containing 20 mM of K + (E max : 102.83 ± 2.10%; pD2: 7.73 ± 0.04, n=6), suggesting the participation of K + channels in the relaxation. The presence of the specific soluble guanylyl cyclase (sGC) inhibitor, ODQ (10μM), abolished the vasorelaxant effect (E max : 15.38 ± 11.85%, n=7). Pre-incubation with cyclopiazonic acid (CPA) (10μM), inhibitor of sarcoendoplasmic reticulum calcium ATPase (SERCA), shifted the relaxation concentration-response to the right (E max : 106.17 ± 3.06%; pD2: 7.69 ± 0.04, n=6). Interestingly, repeated NONO2P administration did not induce tachyphylaxis, and NONO2P presented similar maximum efficacy to sodium nitroprusside (SNP) (E max : 114.24 ± 3.47%; pD2: 9.40 ± 0.04, n=6). Moreover, NONO2P lowered blood pressure in normotensive rats. Conclusion: The endothelium-independent vasorelaxant effect induced by NONO2P involves both sGC, SERCA and K + channel activation, and NONO2P does not appear to cause tachyphylaxis. NONO2P is able to promote vasorelaxation with the same magnitude as SNP. Finally, NONO2P reduces blood pressure, becoming a promising molecule as a novel therapeutic alternative for the treatment of cardiovascular diseases.

Effects of fumarate on renal vascular reactivity and the modulation of blood pressure in normotensive rats: Possible contribution of the nitric oxide synthase-nitric oxide system

Introduction: Fumarate, the tricarboxylic acid (TCA) cycle intermediary, has been linked to nitric oxide (NO) produc­tion. NO plays a prominent role in the physiological regulation of blood pressure and renal hemodynamics. This study is aimed to investigate any contribution of fumarate to blood pressure and renal hemodynamics in normotensive rats with a possible link to the nitrergic system.
 Materials and methods: Fumarate (1, 3 and 10 μmol) was injected into isolated perfused kidneys, pre-constricted with epinephrine (30 μM). The fumarase inhibitor, pyromellitic acid (PMA) (1, 3 and 10 μM), was used to perfuse the iso­lated kidney and perfusate was collected for nitric oxide and fumarate assays. An acute blood pressure study involved the injection of bolus doses of fumarate (0.1, 0.3 and 1 μg/kg, iv) or PMA (1, 3 and 10 μg/kg, iv) to normotensive rats in the presence of N(ω)-nitro-L-arginine methyl ester (L-NAME) (10 mg/kg, iv) or PMA (1, 3 and 10 μg/kg).
 Results and discussion: Fumarate reduced perfusion pressure and elicited a peak reduction at the highest dose. Per­fusing the kidney with PMA caused a paradoxical increase in perfusion pressure (70%, p<0.05), compared to baseline. Bolus doses of fumarate reduced blood pressure (-29.3±6.2 mmHg, p<0.05), cortical blood flow (CBF) and increased medullary blood flow (MBF). L-NAME did not abolish the vasodilatory effect of fumarate, but reduced the magnitude of response (50%, p<0.05). PMA did not significantly affect the vasodilatory effect of fumarate (p>0.05).
 Conclusion: These data suggest that fumarate exerts a vasodilatory effect on renal and systemic hemodynamics that may partly involve the nitric oxide signaling.
 Grapgical abstract:

Abstract P169: Effects Of Saccharina Japonica Intake On Blood Pressure In Normotensive Rats Fed A High-salt Diet

Objectives: One of foods used for Japanese cuisine “Washoku” is brown algae, including Saccharina japonica (SJ). The intake of SJ is reported to decrease blood pressure (BP) in spontaneously hypertensive rats in some studies, and in 2-kidney, 1-clip hypertensive (2K1C) rats in our studies. Several studies indicated that dietary fibers contained in SJ, such as alginate and fucoidan, may play an important role in reducing BP. We previously demonstrated that SJ intake did not decrease BP in normotensive rats fed a normal-salt (NS) diet. We also observed that the suppression of BP rise by SJ intake was stronger in 2K1C rats fed a high-salt (HS) diet than in 2K1C rats fed an NS diet. An HS diet may lead to the development of hypertension in both humans and rats. However, to our knowledge, it has not been reported that the effect of SJ intake on BP in normotensive rats fed an HS diet. In this study, we compared the effects of SJ intake on BP between in normotensive and hypertensive rats when fed an HS diet. Methods: Male Sprague Dawley rats (6 wks) were treated with sham operation (SHAM) or clipping the left renal artery (2K1C). After surgery, rats were received a control diet (CTL) or a diet contained 5.0% (5 of 100, w/w) SJ, with an NS (0.7% NaCl) or HS (6.0% NaCl) in diets for 6 weeks. Systolic BP (SBP) was measured by a tail-cuff method every week. At the end of the protocol, mean arterial pressure (MAP) was measured in each rat under anesthesia. Results and Discussion: Analysis of variance showed that SBP was significantly higher in 2K1C-HS-CTL than in SHAM-HS-CTL (P<0.001, 156±4 vs 131±2 mmHg at the 6th week), and that SBP was lower in 2K1C-HS-SJ (146±3 mmHg) than in 2K1C-HS-CTL (P<0.05). On the other hand, there were no significant differences in SBP among SHAM groups. MAP in 2K1C-HS-CTL rats was significantly higher than that in SHAM-HS-CTL rats (153±2 vs 132±4 mmHg, P<0.005). MAP in 2K1C-HS-SJ (140±5 mmHg) rats was significantly lower than that in 2K1C-HS-CTL rats (P<0.05). There were no significant differences in MAP among SHAM groups. These findings suggested that SJ intake has an antihypertensive effect in a hypertensive model of rats, but no effect of lowering BP in a normotensive model of rats, unlike antihypertensive drugs, which reduce BP in both hypertensive and normotensive model.

Phytochemical analysis and hypotensive activity of Ipomoea pes-caprae on blood pressure of normotensive rats

Abstract Ipomoea pes-caprae (Convolvulaceae), popularly known as “salsa-da-praia”, is used in folk medicine for the treatment of several diseases, including hypertension. The aim of this research was to evaluate hypotensive activity attributed to this species and identify the bioactive compounds responsible for this effect. Hydroalcoholic extract of aerial parts of Ipomoea pes-caprae (PIEA) was fractionated by column chromatography with Amberlite XAD-2, thus achieving a methanolic fraction (PIEA-M). The chemical profile investigation of PIEA-M was conducted by Ultra Performance Liquid Chromatography coupled to Mass Spectrometry (UPLC-MS) and compound isolation through High Performance Countercurrent Chromatography (HPCCC). Hemodynamic evaluations of PIEA, PIEA-M and isolated compounds were carried out on normotensive rats. The locomotor activity of PIEA and PIEA-M were performed by Rota Rod test using Swiss mice. UPLC-MS analysis of PIEA-M led to the identification of 11 compounds corresponding to seven phenolic acids and four flavonoids. By means of HPCCC, quercetin 6”-O-acetyl-3-O- glucoside (1), a mixture of quercetin-3-O-galactoside and quercetin-3-O- glucoside (2) and quercetin 3-O-glucoside (3) were isolated. PIEA, PIEA-M and the obtained compounds (1 and 2) significantly reduced blood pressure. Also, PIEA and PIEA-M caused significant impairment on mice locomotor activity. These results indicate the potential of Ipomoea pes-caprae as a source of hypotensive agents suggesting that phenolic compounds present in the species are responsible for its hypotensive activity.

In renovascular hypertension, TNF-α type-1 receptors in the area postrema mediate increases in cardiac and renal sympathetic nerve activity and blood pressure.

Neuroinflammation is a common feature in renovascular, obesity-related, and angiotensin II mediated hypertension. There is evidence that increased release of the pro-inflammatory cytokine tumour necrosis factor-α (TNF-α) contributes to the development of the hypertension, but the underlying neural mechanisms are unclear. Here, we investigated whether TNF-α stimulates neurons in the area postrema (AP), a circumventricular organ, to elicit sympathetic excitation, and increases in blood pressure (BP). In rats with renovascular hypertension, AP neurons that expressed TNF-α type-1 receptor (TNFR1) remained constantly activated (expressed c-Fos) and injection of TNFR1 neutralizing antibody into the AP returned BP (systolic: ∼151 mmHg) to normotensive levels (systolic: ∼108 mmHg). Nanoinjection of TNF-α (100 pg/50 nL) into the AP of anaesthetized normotensive rats increased BP (∼16 mmHg) and sympathetic nerve activity, predominantly to the heart (∼53%), but also to the kidneys (∼35%). These responses were abolished by prior injection of a TNFR1 neutralizing antibody (1 ng/50 nL) within the same site. TNFR1 were expressed in the somata of neurons activated by TNF-α that were retrogradely labelled from the rostral ventrolateral medulla (RVLM). These findings indicate that in renovascular hypertension, blocking TNFR1 receptors in the AP significantly reduces BP, while activation of TNFR1 expressing neurons in the AP by TNF-α increases BP in normotensive rats. This is mediated, in part, by projections to the RVLM and an increase in both cardiac and renal sympathetic nerve activity. These findings support the notion that proinflammatory cytokines and neuroinflammation are important pathological mechanisms in the development and maintenance of hypertension.

Early urinary biomarkers of renal tubular damage by a high-salt intake independent of blood pressure in normotensive rats.

Dietary sodium intake has been associated with progression to chronic kidney disease (CKD) as well as hypertension. A high-salt intake causes renal damage independent of hypertension. Because traditional renal biomarkers are insensitive, it is difficult to detect renal injury induced by a high-salt intake, especially in normotensive patients. Here, we investigated whether newly developed renal biomarkers could be detected earlier than traditional biomarkers under a high-salt intake, in normotensive rats. Male Wistar Kyoto rats (WKY) received a regular (0.8% NaCl) or salt-loaded (2, 4, and 8% NaCl) diet from 9 to 17weeks of age. A urine sample was obtained once a week and urinary vanin-1, neutrophil gelatinase-associated lipocalin (NGAL), and kidney injury molecule-1 (Kim-1) were measured. At 17weeks of age, 8% salt-loaded WKY showed histopathological renal tubular damage and elevated Rac1 activity in renal tissues. Although there was no significant increase in serum creatinine, urinary albumin, N-acetyl-β-D-glucosaminidase (NAG), or Kim-1 during the study period among the groups, urinary vanin-1 and NGAL significantly increased in 8% salt-loaded WKY from 10 to 17weeks of age. These results suggest that urinary vanin-1 and NGAL, which might be induced by salt per se, are potentially earlier biomarkers for renal tubular damage in normotensive rats under a high-salt intake.

Cerebral Aβ40 and systemic hypertension

Mid-life hypertension and cerebral hypoperfusion may be preclinical abnormalities in people who later develop Alzheimer’s disease. Although accumulation of amyloid-beta (Aβ) is characteristic of Alzheimer’s disease and is associated with upregulation of the vasoconstrictor peptide endothelin-1 within the brain, it is unclear how this affects systemic arterial pressure. We have investigated whether infusion of Aβ40 into ventricular cerebrospinal fluid modulates blood pressure in the Dahl salt-sensitive rat. The Dahl salt-sensitive rat develops hypertension if given a high-salt diet. Intracerebroventricular infusion of Aβ induced a progressive rise in blood pressure in rats with pre-existing hypertension produced by a high-salt diet (p < 0.0001), but no change in blood pressure in normotensive rats. The elevation in arterial pressure in high-salt rats was associated with an increase in low frequency spectral density in systolic blood pressure, suggesting autonomic imbalance, and reduced cardiac baroreflex gain. Our results demonstrate the potential for intracerebral Aβ to exacerbate hypertension, through modulation of autonomic activity. Present findings raise the possibility that mid-life hypertension in people who subsequently develop Alzheimer’s disease may in some cases be a physiological response to reduced cerebral perfusion complicating the accumulation of Aβ within the brain.

Chemical Composition and Hypotensive Effect of Campomanesia xanthocarpa.

Campomanesia xanthocarpa is known in Brazil as Guabiroba and is popularly used for various diseases, such as inflammatory, renal, and digestive diseases and dyslipidemia. The aim of the study was to analyze the chemical composition and investigate the effects of aqueous extract of C. xanthocarpa on the blood pressure of normotensive rats, analyzing the possible action mechanism using experimental and in silico procedures. The extract was evaluated for total phenolic compounds and total flavonoid content. The chemical components were determined by HPLC analyses. Systolic and diastolic blood pressure and heart rate were measured with extract and drugs administration. The leaves of C. xanthocarpa presented the relevant content of phenolics and flavonoids, and we suggested the presence of chlorogenic acid, gallic acid, quercetin, and theobromine. The acute administration of aqueous extract of C. xanthocarpa has a dose-dependent hypotensive effect in normotensive rats, suggesting that the action mechanism may be mediated through the renin-angiotensin system by AT1 receptor blockade and sympathetic autonomic response. Docking studies showed models that indicated an interaction between chlorogenic acid and quercetin with the AT1 receptor (AT1R) active site. The findings of these docking studies suggest the potential of C. xanthocarpa constituents for use as preventive agents for blood pressure.

PP.35.02] EFFECT OF ANGIOTENSIN RECEPTOR STIMULATION IN THE ROSTRAL VENTROLATERAL MEDULLA ON BLOOD PRESSURE IN NORMOTENSIVE RATS

Objective: There is increasing evidence that glutamate and gamma-aminobutyric acid (GABA) interact within the rostral ventrolateral medulla (RVLM) modulating the central regulation of blood pressure and sympathetic tone. Angiotensin II (Ang II) is the most important effector in the renin-angiotensin-aldosterone system (RAAS) mediating its actions through the angiotensin II type 1 receptor (AT1R) and angiotensin II type 2 receptor (AT2R). The AT2R is part of the protective arm of the RAAS and mediates opposing effects counterbalancing the AT1R mediated actions. The selective and specific AT2R agonist Compound 21 (C21) is a useful research tool to investigate the AT2R mediated effects. Design and method: In the present study we assess through local stimulation and blockade of AT1R and AT2R the possible role of the brain RAAS at the level of the RVLM on the regulation of blood pressure. In vivo microdialysis, for measurement of extracellular glutamate and GABA levels, was carried out in the RVLM of conscious normotensive Wistar rats while locally infusing C21, Ang II, and PD123319. Glutamate and GABA levels were quantified by HPLC. Subsequently, the effect of central administration of C21, Ang II, and PD123319 on mean arterial pressure was assessed with a pressure transducer for continuous monitoring. Results: Infusion of Ang II into the RVLM significantly increased glutamate levels (P < 0.05) and significantly decreased GABA levels (P < 0.01). Infusion of the AT2R agonist C21 (0.05 μg/μl/h) tended to decrease glutamate and increase GABA levels, while absolutely no change was seen when co-infusing C21 together with the AT2 receptor antagonist PD123319. C21 infusion (0.05 μg/μl/h) significantly lowered blood pressure (P < 0.01). These responses were abolished by co-administration of C21 and PD123319. No changes in neurotransmitter levels or effects on blood pressure were seen with PD123319 infusion alone. Conclusions: These data demonstrate that acute specific stimulation of AT2R in the RVLM by local C21 infusion reduces blood pressure in normotensive rats, and suggests that decreases in local glutamate and increases in GABA levels may be involved in the sympatho-inhibitory action underlying this hypotensive response.

Chemically Homogenous Compounds with Antagonistic Properties at All α1-Adrenoceptor Subtypes but not β1-Adrenoceptor Attenuate Adrenaline-Induced Arrhythmia in Rats

Studies proved that among all α1-adrenoceptors, cardiac myocytes functionally express only α1A- and α1B-subtype. Scientists indicated that α1A-subtype blockade might be beneficial in restoring normal heart rhythm. Therefore, we aimed to determine the role of α1-adrenoceptors subtypes (i.e., α1A and α1B) in antiarrhythmic effect of six structurally similar derivatives of 2-methoxyphenylpiperazine. We compared the activity of studied compounds with carvedilol, which is β1- and α1-adrenoceptors blocker with antioxidant properties. To evaluate the affinity for adrenergic receptors, we used radioligand methods. We investigated selectivity at α1-adrenoceptors subtypes using functional bioassays. We tested antiarrhythmic activity in adrenaline-induced (20 μg/kg i.v.), calcium chloride-induced (140 and 25 mg/kg i.v.) and barium chloride-induced (32 and 10 mg/kg i.v.) arrhythmia models in rats. We also evaluated the influence of studied compounds on blood pressure in rats, as well as lipid peroxidation. All studied compounds showed high affinity toward α1-adrenoceptors but no affinity for β1 receptors. Biofunctional studies revealed that the tested compounds blocked α1A-stronger than α1B-adrenoceptors, but except for HBK-19 they antagonized α1A-adrenoceptor weaker than α1D-subtype. HBK-19 showed the greatest difference in pA2 values—it blocked α1A-adrenoceptors around seven-fold stronger than α1B subtype. All compounds showed prophylactic antiarrhythmic properties in adrenaline-induced arrhythmia, but only the activity of HBK-16, HBK-17, HBK-18, and HBK-19 (ED50 = 0.18–0.21) was comparable to that of carvedilol (ED50 = 0.36). All compounds reduced mortality in adrenaline-induced arrhythmia. HBK-16, HBK-17, HBK-18, and HBK-19 showed therapeutic antiarrhythmic properties in adrenaline-induced arrhythmia. None of the compounds showed activity in calcium chloride- or barium chloride-induced arrhythmias. HBK-16, HBK-17, HBK-18, and HBK-19 decreased heart rhythm at ED84. All compounds significantly lowered blood pressure in normotensive rats. HBK-18 showed the strongest hypotensive properties (the lowest active dose: 0.01 mg/kg). HBK-19 was the only compound in the group, which did not show hypotensive effect at antiarrhythmic doses. HBK-16, HBK-17, HBK-18, HBK-19 showed weak antioxidant properties. Our results indicate that the studied 2-methoxyphenylpiperazine derivatives that possessed stronger α1A-adrenolytic properties (i.e., HBK-16, HBK-17, HBK-18, and HBK-19) were the most active compounds in adrenaline-induced arrhythmia. Thus, we suggest that the potent blockade of α1A-receptor subtype is essential to attenuate adrenaline-induced arrhythmia.

Design, synthesis, anticonvulsant, and antiarrhythmic properties of novel N-Mannich base and amide derivatives of β-tetralinohydantoin.

5,5-Diphenylhydantoin (Phenytoin) is a well-known anticonvulsant and antiarrhythmic drug which may cause unwanted side effects. In order to avoid the adverse effects of phenytoin, especially on the central nervous and cardiovascular systems, two small series of amine derivatives (Mannich bases) and amide ones were designed containing β-tetralinohydantoin system. In preliminary studies, some of arylpiperazinylmethyl derivatives with a β-tetralinohydantoin moiety were effective in screening anticonvulsant tests in mice. These new amine and amide derivatives of β-tetralinohydantoin were evaluated in standard anticonvulsant screens (maximal electroshock (MES) or pentylenetetrazole (scPTZ) seizure tests) and their neurotoxicity was assessed in standardized rotarod tests. Additionally, due to structural features (a hydantoin ring), influence on antiarrhythmic activity, electrocardiogram components and blood pressure was tested in rats. The new N-Mannich bases were effective in maximal electroshock or pentylenetetrazole seizures screens; and the most interesting compound 4 (1-{[4-(1-phenyethyl)-piperazin-1-yl]methyl}-3',4'-dihydro-1'H,2H,5H-spiro[imidazolidine-4,2'-naphthalene]-2,5-dione) displayed anticonvulsant activity in both the aforementioned tests. Furthermore, compound 6, an amide derivative of β-tetralinohydantoin, displayed significant antiarrhythmic activity in a barium chloride-induced arrhythmia model (ED50 16.3mg/kg), but it was devoid of anticonvulsant protection. None of the tested compounds affected the electrocardiogram components or blood pressure in normotensive rats. All new N-Mannich bases containing the β-tetralinohydantoin system and 1-phenylalkylpiperazine were classified to Anticonvulsant Screening Program 1st class. In contrast, our results suggested that the introduction of an amide bond in the alkyl side chain of the β-tetralinohydantoin system abolished the anticonvulsant activity, but not the antiarrhythmic one. However, further studies are required for a definitive conclusion.

Orchidectomy reduces blood pressure, but testosterone increases it in intact and orchidectomized normotensive rats

Background: The cardioprotective effect of estrogen has been well documented, and the effect of testosterone on blood pressure (BP) is controversial and remains inconclusive. Aim: The present study is aimed at investigating the effect of testosterone on BP in normotensive rats. Materials and Methods: In a blind study, 30 male albino rats (200-250 g) were divided into 5 oral treatment groups (n = 6 rats each) as follows: Groups I and II were intact rats that received 1 ml/kg normal saline (vehicle) and 25 mg/kg testosterone subcutaneously for 24 days. Group III was sham-operated and received normal saline for 24 days. Groups IV and V were bilaterally orchidectomized and received normal saline and 25 mg/kg testosterone subcutaneously for 24 days. Results: The systolic BP (SBP), diastolic BP (DBP), pulse pressure (PP), and mean arterial pressure (MAP) of the sham-operated rats that received normal saline were not significantly different from the intact (control) rats that received normal saline (P > 0.05). Testosterone treatment in control rats caused a sustainably higher SBP (P 0.05) was significantly reduced in orchidectomized rats that received normal saline when compared to control. However, administration of testosterone in orchidectomized rats abolished orchidectomy-induced reduction in SBP, DBP, MAP, but not PP and further increased them above the control level (P Conclusion: This study shows that testosterone is prohypertensive in normotensive rats.

Purification and characterization of angiotensin converting enzyme-inhibitory peptides derived from Stichopus horrens: Stability study against the ACE and inhibition kinetics

Stichopus horrens is the most popular species of sea cucumber due to strong beliefs of its numerous medicinal properties. In this study, ACE-inhibitory peptides of S. horrens generated through enzymatic hydrolysis using Alcalase were isolated. Three peptides EVSQGRP, CRQNTLGHNTQTSIAQ and VSRHFASYAN were found to exhibit high inhibition potency with IC50 values of 0.05, 0.08 and 0.21 mM, respectively. It was found that the EVSQGRP, VSRHFASYAN and SAAVGSP exhibiting mixed inhibition patterns were susceptible to degradation by ACE as well, suggesting that the mixed-mode inhibition could be a result of new generated peptide fragments while CRQNTLGHNTQTSIAQ inhibited ACE in a non-competitive manner. In-vivo ACE inhibition studies showed that 400 mg/kg of Alcalase-generated proteolysate stabilized the blood pressure in normotensive rats. These results suggest that the hydrolysed protein components of S. horrens possess bioactive peptides that can be exploited as functional food ingredients against hypertension.

Involvement of the median preoptic nucleus in blood pressure control

Studies have demonstrated that median preoptic nucleus (MnPO) neurons play a role in organizing the cardiovascular responses induced by changes in the circulating blood volume. The present study examined whether the MnPO controls cardiovascular function. Male Wistar normotensive (NT) rats and spontaneously hypertensive rats (SHRs; 250–300g) were anesthetized with urethane (1.2gkg−1, i.v.) and instrumented for recordings of mean arterial blood pressure (MAP) and renal blood flow (RBF). The renal vascular conductance (RVC) was calculated as the RBF:MAP ratio and was expressed as a percentage of the baseline value. In the NT rats (n=6), MnPO inhibition produced a MAP reduction (−8.1±1.1mmHg, p<0.05). In the SHRs (n=6), the MAP response to MnPO inhibition was significantly greater (−22.3±4mmHg, p<0.05) than in the NT rats. Furthermore, the increase in the RVC was higher in the SHRs (10.9±3.3%, p<0.05). Histological analyses confirmed that the injection sites were confined to the MnPO. We conclude that the MnPO is involved in the tonic regulation of blood pressure in NT rats. Moreover, the greater cardiovascular response to MnPO inhibition observed in the SHRs strongly suggests that the MnPO may contribute to the pathophysiology of essential hypertension.

Abstract 524: Vinegar Enhanced the Anti-hypertensive Effect of Saccharina Japonica Intake in Rats With 2-kidney, 1-clip Renovascular Hypertension

Objective: Saccharina japonica (SJ) is one of brown algae and is cultivated or grows wild in Japan and neighbor countries. SJ is rich in alginate, the intake of which was reported to decrease blood pressure (BP) in spontaneously hypertensive rats. It is also rich in fucoidan, which was reported to improve the renal blood flow in rats with acute renal failure. We recently observed that intake of SJ decreased BP in 2-kidney, 1-clip renovascular hypertensive (2K1C) rats, probably through nitric oxide, and did not change BP in normotensive rats. In Japan, there are many traditional processed foods made of SJ with vinegar, which is originally used for softening SJ and raising its preserving property. Vinegar is also suggested to suppress angiotensin-converting enzyme activity. In this study, we investigated the interactive effects of SJ and vinegar on BP in 2K1C rats. Methods: Male Sprague-Dawley rats (6 wks) were treated with sham operation (SHAM) or clipping the left renal artery (2K1C). After surgery, SHAM or 2K1C rats started receiving a control diet (CTL) or a diet containing 5.0% (w/w) freeze-dried SJ powder (SJ) for 6 weeks, and a tap water (Veh) or a water containing 5.0% (v/v) of 4.3% acidity rice vinegar (VG). The systolic BP (SBP) was measured by a tail-cuff method every week. At the end of the protocol, mean arterial BP (MAP) was measured in each rat under anesthesia. Then, thoracic aorta was removed and the section of aorta was stained with hematoxylin and eosin. Results: Analysis of variance revealed significant effects in time, animal model (SHAM vs 2K1C), diet (CTL vs SJ) and model x diet ( P &lt; 0.001, each), but not in water (Veh vs VG) or model x water. At the end of the protocol, in CTL-Veh, 2K1C was higher in SBP than SHAM (179 ± 33 vs 130 ± 20 mmHg, P &lt; 0.001). In 2K1C-Veh, the SJ diet decreased SBP (156 ± 6 mmHg) compared with CTL ( P &lt; 0.05). Vinegar did not significantly change SBP (184 ± 19 mmHg) in 2K1C-CTL, but decreased SBP (142 ± 11 mmHg) in 2K1C-SJ ( P &lt; 0.05) as low as in SHAM-SJ-VG (139 ± 3 mmHg, P = NS). The observations in MAP were similar to in the SBP. Moreover, compared to SHAM, 2K1C-CTL-Veh showed the aortic media thickening, which was reduced in 2K1C-SJ-Veh/VG. Conclusion: A certain daily intake of vinegar did not lower BP by itself, but enhanced the BP reduction by a SJ diet, in 2K1C rats.

Discovery of 2,8-diazaspiro[4.5]decane-based trisubstituted urea derivatives as highly potent soluble epoxide hydrolase inhibitors and orally active drug candidates for treating hypertension

We identified 2,8-diazaspiro[4.5]decane-based trisubstituted urea derivatives as highly potent soluble epoxide hydrolase (sEH) inhibitors and orally active agents for treating hypertension. Docking studies using human and murine sEH X-ray crystal structures revealed steric hindrance around the side chain of Phe406 of murine sEH. The trifluoromethyl moiety (11) was replaced with a trifluoromethoxy moiety (12) to prevent steric clash, and improved murine sEH inhibitory activity was observed. The oral administration of 12, 20, and 37 at a dose of 30mg/kg reduced blood pressure in spontaneously hypertensive rat, but had little effect on blood pressure in normotensive rat.

Relaxant effect of all-trans-retinoic acid via NO-sGC-cGMP pathway and calcium-activated potassium channels in rat mesenteric artery

Intraperitoneal injection of all-trans-retinoic acid (ATRA) results in a reduction of blood pressure in spontaneously hypertensive rats. However, the mechanisms involved in this effect are not clear. We hypothesized that ATRA may relax resistance arteries. In this study, we found that ATRA relaxed phenylephrine-preconstricted mesenteric arterial rings, which were abrogated by the removal of the endothelium. Pretreatment of endothelium-intact arterial rings with an inhibitor of endothelial nitric oxide (NO) synthase, N(G)-nitro-l-arginine methyl ester (l-NAME), or soluble guanylyl cyclase, 1H-[1,2,4]-oxadiazole-[4,3-α]-quinoxaline-1-one, reduced the vasorelaxant effect of ATRA. Incubation of mesenteric arterial rings with ATRA increased the production of NO and cGMP, which were blocked by N(G)-nitro-l-arginine methyl ester. The vasorelaxant effect of ATRA was markedly attenuated in the presence of an inhibitor of big conductance calcium-activated potassium channels (charybdotoxin), but not with an inhibitor of voltage-dependent potassium channel (4-aminopyridine) or ATP-sensitive potassium channel (glibenclamide). Activation of retinoic acid receptors (RARs) with CH55 or retinoic X receptors (RXRs) with LGD1069 induced the vasorelaxation of phenylephrine-preconstricted mesenteric arterial rings. The RAR (BMS493) and RXR (UVI3003) antagonists blocked the ATRA-induced vasorelaxation. The vasorelaxant effect ATRA is physiologically relevant because the intravenous infusion of ATRA decreased blood pressure in normotensive rats. We conclude that ATRA relaxes resistance vessels via both RARs and RXRs receptors that are mediated by the endothelium-dependent NO-cGMP pathway, which may participate in the control of blood pressure.

Effect of the flavonoid fraction of Lithocarpus polystachyus Rehd. on spontaneously hypertensive and normotensive rats

Ethnopharmacological relevanceLilhocarpus polystachys Rehd. (Sweet Tea, ST) is a folk herbal medicine that has been traditionally used as a natural remedy for hypertension in China, whose mechanism remains unveiled. Flavonoid fraction is considered as the major active components in ST. This study aimed to provide experimental evidence for the anti-hypertension activity of flavonoid fraction of ST (ST-F) and investigate the underlying mechanism. The effect of ST-F on the blood pressure of normotensive rats was also to be determined. Materials and methodsSpontaneously hypertensive rats (SHRs) were treated with ST-F daily for 10 weeks. Blood pressure of SHRs was measured before and biweekly during ST-F treatment. Subsequently, animals were sacrificed either immediately at the end of treatment or 2 weeks after ST-F treatment discontinuance. The activities of plasma rennin (PRA), angiotensin II (Ang-I), endothelin (ET), nitric oxide (NO), superoxide dismutase (SOD) and malondialdehyde (MDA) were measured as well as skin microcirculatory flux. In normotensive rats, blood pressure was determined after six months' treatment of ST-F. ResultsST-F treatment significantly reduced the blood pressure of SHRs along with decreasing plasma levels of PRA and Ang II. ST-F did not show obvious effects on plasma levels of ET, NO or SOD, but it significantly decreased the plasma level of MDA and improved skin microcirculatory flux. Compared to the anti-hypertensive drug enalapril, ST-F showed a modest effect on lowering blood pressure of SHRs without obvious withdrawal reactions. But long-term intake of ST-F did not change the blood pressure in normotensive rats. ConclusionST-F had an antihypertensive effect on SHRs. The underlying mechanism could be related to modulation on the rennin–angiotensin–aldosterone system (RAAS) and antioxidation system, as well as regulation of skin microcirculation. Compared to its anti-hypertensive effect on SHRs, ST-F did not cause hypotension in normotensive rats. The results indicated that ST-F could potentially be used as natural drugs or functional foods for preventing hypertension.

Involvement of the Median Preoptic Nucleus in the arterial blood pressure regulation

Studies have been shown that Median Preoptic Nucleus (MnPO) neurons have a great influence in the cardiovascular responses induced by changes in circulating volume. The present study sought to determine the participation of MnPO in the cardiovascular control. Male Wistar normotensive (NT) and spontaneously hypertensive (SH) rats (280–320g) were anesthetized with urethane (1.2 g/kg, i.v.) and instrumented for mean arterial blood pressure (MAP) and renal blood flow (RBF) recordings. Renal vascular conductance (RVC) was calculated as the ratio RBF/MAP and expressed as percentage of baseline. In NT rats (n=7), inhibition of MnPO nucleus produced a significant hypotension (−7 ± 1.5 mmHg) and renal vasodilation (5.3 ± 1.2% above baseline). In SH rats (n=8), hypotension response was significantly greater (−15 ± 2.7 mmHg, p&lt;0.05) than NT rats. We also observed an increase of RVC (8.4 ± 2.4% above baseline) in HT rats. Analysis of the spread of dye nanoinjected at the end of the experiment showed that the drug injection sites were confined to the MnPO. We conclude that the MnPO nucleus is involved in the tonic regulation of blood pressure in NT rats. Moreover, the increase of neuronal activity in the MnPO may contribute to sympathoexcitation and maintenance of hypertension in SH rats. Supported by CNPq (477832/2010‐5; GRP).