Conscious Normotensive Rats Research Articles

The Dual Cardiovascular Effect of Centrally Administered Clonidine: A Comparative Study between Pentobarbital- and Ketamine/Xylazine-Anesthetized Rats

The administration of the α2-adrenergic receptor agonist clonidine via intracerebroventricular route produces hypotension in pentobarbital-anesthetized rats and pressor responses in conscious normotensive rats. We explored the impact of different anesthetics on the central nervous system-dependent cardiovascular effects of clonidine. Normotensive male Wistar rats with guide cannulas previously implanted in the cerebroventricular system were anesthetized with pentobarbital or ketamine/xylazine and prepared for blood pressure measurement. The animals received intracerebroventricular injections of 10 μg clonidine or 0.6 μg dexmedetomidine, and the effects on the systolic, diastolic, mean arterial pressure, and heart rate were evaluated. The influence of 5 μg yohimbine, a selective α2-adrenergic receptor antagonist, was also assessed. The i.c.v. microinjection of clonidine decreased all three components of systemic arterial pressure and the heart rate of pentobarbital-anesthetized rats. On the other hand, clonidine increased the blood pressure and generated a less intense reduction in the heart rate of ketamine/xylazine-anesthetized rats. The pressor and bradycardic effects of clonidine in ketamine/xylazine-anesthetized animals were reproduced by dexmedetomidine, a more selective α2-adrenergic receptor agonist. Notably, the previous intracerebroventricular injection of yohimbine significantly inhibited the hypertensive effect of clonidine and dexmedetomidine. This study discloses that while normotensive rats anesthetized with pentobarbital show hypotensive responses, the stimulation of α2-adrenergic receptors increases the blood pressure in rats under ketamine/xylazine-induced anesthesia, reproducing the effects seen in conscious normotensive animals. Recognizing the mechanisms involved in these differences may allow us to understand better the final effects of clonidine and other α2-adrenergic receptor agonists in the central nervous system, contributing to the repurposing of these drugs.

The Effect of Unilateral Nephrectomy on Arterial Blood Pressure Variability in Spontaneously Hypertensive Rats


 
 
 The aim of the current study was to investigate the effects of unilateral nephrectomy (ULN) on fast oscillation of arterial blood pressure in spontaneously hypertensive rats (SHR). Experiments were carried out on conscious normotensive Wistar rats and SHR divided in groups with intact kidneys: W, n = 10; SHR, n = 9 and with unilateral nephrectomy: WN, n = 10; SHRN, n = 10. ULN was performed under general anaesthesia (Nembutal 35 mg/kg b.w. i.p.), eight days before the experiments. Blood pressure variability was investigated by means of spectral analysis of systolic (SAP) diastolic (DAP) and mean (MAP) arterial blood pressure, estimated in directly registered arterial blood pressure wave. In SAP, DAP and MAP spectrograms, derived by Lab View software equipment, the spectral power (P) in low (LF, 20–195 mHz), mid (MF, 195–605 mHz) and high frequency (HF, 605—3000 mHz) bands was calculated. PLF in SAP spectrograms increased after ULN both in Wistar rats and SHR. ULN led to decrease of PMF in SAP, DAP and MAP spectrograms only in SHR. The ULN provokes changes in blood pressure variability in different manner in the normotensive and the spontaneously hypertensive rats. In addition to humorally-mediated low-frequency oscillations, ULN in SHR also af- fected the spectral characteristics of the arterial pressure in which sympathetic nervous activity operates.
 
 

LIT01-196, a Metabolically Stable Apelin-17 Analog, Normalizes Blood Pressure in Hypertensive DOCA-Salt Rats via a NO Synthase-dependent Mechanism.

Apelin is a neuro-vasoactive peptide that plays a major role in the control of cardiovascular functions and water balance, but has an in-vivo half-life in the minute range, limiting its therapeutic use. We previously developed LIT01-196, a systemically active metabolically stable apelin-17 analog, produced by chemical addition of a fluorocarbon chain to the N-terminal part of apelin-17. LIT01-196 behaves as a potent full agonist for the apelin receptor and has an in vivo half-life in the bloodstream of 28 min after intravenous (i.v.) and 156 min after subcutaneous (s.c.) administrations in conscious normotensive rats. We aimed to investigate the effects of LIT01-196 following systemic administrations on arterial blood pressure, heart rate, fluid balance and electrolytes in conscious normotensive and hypertensive deoxycorticosterone acetate (DOCA)-salt rats. Acute i.v. LIT01-196 administration, in increasing doses, dose-dependently decreases arterial blood pressure with ED50 values of 9.8 and 3.1 nmol/kg in normotensive and hypertensive rats, respectively. This effect occurs for both via a nitric oxide-dependent mechanism. Moreover, acute s.c. LIT01-196 administration (90 nmol/kg) normalizes arterial blood pressure in conscious hypertensive DOCA-salt rats for more than 7 h. The LIT01-196-induced blood pressure decrease remains unchanged after 4 consecutive daily s.c. administrations of 90 nmol/kg, and does not induce any alteration of plasma sodium and potassium levels and kidney function as shown by the lack of change in plasma creatinine and urea nitrogen levels. Activating the apelin receptor with LIT01-196 may constitute a novel approach for the treatment of hypertension.

The intermediary role of the central cyclooxygenase / lipoxygenase enzymes in intracerebroventricular injected nesfatin-1-evoked cardiovascular effects in rats

That nesfatin-1 is a neuromodulatory peptide for the cardiovascular system is well documented. Several central receptors have been shown to mediate the cardiovascular effects of nesfatin-1. Immunohistochemistry and Western blot studies showed that nesfatin-1 activated the expression of the central cyclooxygenase (COX) -1, -2 and lipoxygenase (LOX). In addition, microdialysis study showed that nesfatin-1 increased the release of total prostaglandins and leukotrienes from the hypothalamus. The present study investigated whether the central COX and LOX enzymes have a direct mediating role in the MAP and HR responses of nesfatin-1.Intracerebroventricularly administered nesfatin-1 produced dose-dependent pressor and phasic HR responses in normotensive conscious rats Sprague Dawley. Central pretreatment with a COX1/2 inhibitor, ibuprofen, completely blocked the nesfatin-1-induced responses. However, central pretreatment with a nonselective LOX inhibitor, nordihydroguaiaretic acid, partially attenuated the cardiovascular responses induced by nesfatin-1.The results suggest that centrally administered nesfatin-1 activates the central enzymes COX and LOX, which may be involved in the cardiovascular responses as a novel central mechanism for nesfatin-1.

The Influence of Anesthesia on the Cardiovascular Effects of Centrally Administered Clonidine

The α2 adrenergic receptor (α2AR) agonists are known to induce hypotensive responses when administered via intracerebroventricular (icv) route in normotensive rats anesthetized with either pentobarbital or urethane. However, the icv injection of α2AR agonists such as clonidine (CLO) produces hypertensive responses in normotensive conscious rats. To date, the effects icv administration of CLO in normotensive rats under ketamine/xylazine anesthesia, a commonly used anesthetic combination in experimental studies, is still unknown. We hypothesized that anesthetic drugs differentially modulate cardiovascular responses to centrally administered CLO. To evaluate this hypothesis, we assessed blood pressure (BP) and heart rate (HR) of normotensive male rats anesthetized with pentobarbital or ketamine/xylazine, both under mechanical ventilation. These animals received CLO (10 μg/5 μL) or dexmedetomidine (DEX; 0.6 μg/5 μL) by icv route. In additional experiments, yohimbine (5 μg/5 μL), a selective α2AR antagonist, was given by icv route 15 min before a second injection of CLO or DEX in ketamine/xylazine anesthetized rats. As widely described, the icv microinjection of CLO decreased the mean arterial pressure (MAP) and HR by 40.73 ± 6.3 mmHg and 134 ± 15 bpm in pentobarbital anesthetized rats (n = 5). On the other hand, in ketamine/xylazine anesthetized rats (n = 6) CLO increased MAP by 29.4 ± 5.1 mmHg and decreased HR by 34 ± 5 bpm, a less pronounced effect when compared with the pentobarbital group (p < 0.0001). Similarly, the icv microinjection of DEX in ketamine/xylazine anesthetized rats (n = 6) increased MAP by 20.8 ± 3.2 mmHg and decreased HR by 51 ± 16 bpm. Notably, yohimbine generated a pattern of hypotensive responses comparable to CLO and DEX. Additionally, after yohimbine administration, both CLO- and DEX-increased MAP were reduced to 9.9 ± 2.3 mmHg and 6.7 ± 1.1 mmHg, respectively (n = 6, p < 0.05), despite the lack of influence of yohimbine in the bradycardia induced by these α2AR agonists in ketamine/xylazine anesthetized rats. This study discloses that in normotensive rats under ketamine/xylazine anesthesia, central administration of CLO produces a hypertensive effect, opposing the findings obtained in pentobarbital-anesthetized rats and resembling the vascular responses described in conscious animals. This data was reproduced by DEX and reduced by yohimbine, suggesting that stimulation of central α2AR takes a preponderant role in this effect. Our results reinforce the relevance regarding the influence of anesthetic choice for studies involving cardiovascular parameters.

Firibastat: An Oral First-in-Class Brain Aminopeptidase A Inhibitor for Systemic Hypertension.

Systemic hypertension is the leading cause of death and disability worldwide. The management of hypertension is challenging in the high-risk patient population with high salt-sensitivity and low serum renin levels. The renin-angiotensin system (RAS) plays a central role in blood pressure (BP) regulation. While we have effective medications to act on peripheral RAS, our understanding of brain RAS and its effect on BP regulation is still in an evolving stage. Brain RAS hyperactivity is associated with the development and maintenance of hypertension. In comparison to peripheral RAS, where angiotensin II is the most crucial component responsible for BP regulation, angiotensin III is likely the main active peptide in the brain RAS. Angiotensin II is metabolized by aminopeptidase A into angiotensin III in the brain. EC33 is a potent inhibitor of brain aminopeptidase A tested in animal models. The use of EC33 in conscious spontaneously hypertensive rats, hypertensive deoxycorticosterone acetate-salt rats, and conscious normotensive rat models leads to a reduction in BP. In order to facilitate the passage of EC33 through the blood-brain barrier, the 2 molecules of EC33 were linked by a disulfide bridge to form a prodrug called RB150. RB150, later renamed as QGC001 or firibastat, was found to be effective in animal models and well-tolerated when used in healthy participants. Firibastat was found to be safe and effective in phase 2 trials, and is now planned to undergo a phase 3 trial. Firibastat has the potential to be groundbreaking in the management of resistant hypertension.

Peripheral Latanoprost Administration Lowers Intraocular Pressure in the Wistar Rat.

PurposeInstillation of latanoprost eye drops into the conjunctival sac to lower intraocular pressure (IOP) is the most frequently used treatment for primary open-angle glaucoma. The aim of this study was to evaluate the influence of latanoprost on IOP in the rat when applied peripherally.MethodsA rodent-dedicated tonometer was used to measure IOP in conscious adult male normotensive Wistar rats habituated to the measurement procedure. Commercially available 0.005% latanoprost solutions were continuously delivered to the periphery of the eye over 7 days using mini-pumps inserted subcutaneously in the animal’s back, and IOP was measured daily. For comparison, a solution containing an equimolar concentration of latanoprost acid, an active compound of latanoprost, was similarly infused into the eyes of different Wistar rats.ResultsContinuous subcutaneous infusion of latanoprost gradually decreased the IOP; the stable nadir of IOP, which was 20% lower than that prior to the start of infusion, was reached on day 3. The effect was statistically significant and fully reversed 2 days after cessation of drug delivery. Continuous subcutaneous application of the solution containing an equimolar amount of latanoprost acid did not appreciably influence the IOP.ConclusionSubcutaneous continuous delivery of latanoprost decreased the IOP in the conscious normotensive Wistar rats in this study. If this effect is confirmed in humans, it may open the possibility of using peripheral systems of drug delivery, which could significantly improve patient compliance.

AT1 Receptor Mediated Hypertensive Response to Ang II in the Nucleus Tractus Solitarii of Normotensive Rats Involves NO Dependent Local GABA Release.

AimIt is well-established that angiotensin II exerts a dampening effect on the baroreflex within the nucleus tractus solitarii (NTS), the principal brainstem site for termination of baroreceptor afferents and which is densely populated with gamma-aminobutyric acid (GABA)ergic neurons and nerve terminals. The present study was designed to investigate whether local release of GABA is involved in the effects mediated by local angiotensin II within the NTS.MethodsIn vivo microdialysis was used for measurement of extracellular glutamate and GABA levels and for infusion of angiotensin II within the NTS of conscious normotensive Wistar rats. The mean arterial pressure (MAP) and heart rate response to local infusion of angiotensin II were subsequently monitored with a pressure transducer under anesthesia. The angiotensin II type 1 receptor (AT1R) antagonist, candesartan, was used to assess whether responses were AT1R dependent and the nitric oxide (NO) synthase inhibitor, N(ω)-nitro-L-arginine methyl ester (L-NAME), was used to assess the involvement of NO in the evoked responses by infusion of angiotensin II. The MAP and heart rate responses were monitored with a pressure transducer.ResultsLocal infusion into the NTS of angiotensin II induced a significant to ninefold significantly increase in extracellular GABA levels; as well as MAP was increased by 15 mmHg. These responses were both abolished by co-infusion of either, the angiotensin II type 1 receptor antagonist, candesartan, or the NO synthase inhibitor, L-NAME, demonstrating that the effect is not only AT1R dependent but also NO dependent. The pressor response to angiotensin II was reversed by co-infusion with the GABAA receptor antagonist, bicuculline. Local blockade of NO synthase decreased both, GABA and glutamate concentrations.ConclusionOur results suggest that the AT1R mediated hypertensive response to angiotensin II within the NTS in normotensive rats is GABA and NO dependent. Nitric oxide produced within the NTS tonically potentiates local GABA and glutamate release.

Hypotensive Response to Angiotensin II Type 2 Receptor Stimulation in the Rostral Ventrolateral Medulla Requires Functional GABA-A Receptors.

Objectives: Angiotensin II, glutamate and gamma-aminobutyric acid (GABA) interact within the rostral ventrolateral medulla (RVLM) and the paraventricular nucleus (PVN) modulating the central regulation of blood pressure and sympathetic tone. Our aim was to assess the effects of local angiotensin II type 2 receptor stimulation within the RVLM and the PVN on neurotransmitter concentrations and mean arterial pressure (MAP).Methods: In vivo microdialysis was used for measurement of extracellular glutamate and GABA levels and for local infusion of the angiotensin II type 2 receptor agonist Compound 21 in the RVLM and the PVN of conscious normotensive Wistar rats. The MAP response to local Compound 21 was monitored with a pressure transducer under anaesthesia. Angiotensin II type 2 receptor selectivity was assessed using the angiotensin II type 2 receptor antagonist PD123319; the GABA-A receptor antagonist bicuculline was used to assess the involvement of GABA-A receptors.Results: Infusion of Compound 21 (0.05 μg/μl/h) in the RVLM significantly increased GABA levels and lowered blood pressure. These effects were abolished by co-infusion with PD123319. No changes in neurotransmitter levels or effects on blood pressure were seen with PD123319 infusion alone. Co-infusion of bicuculline abolished the Compound 21 evoked decrease in MAP. Infusion of Compound 21 within the PVN did not change extracellular neurotransmitter levels nor MAP.Conclusion: Selective stimulation of angiotensin II type 2 receptor within the RVLM by local Compound 21 infusion reduces blood pressure and increases local GABA levels in normotensive rats. This hypotensive response requires functional GABA-A receptors, suggesting that GABAergic neurons are involved in the sympatho-inhibitory action underlying this hypotensive response.

HYPOTENSIVE RESPONSE TO ANGIOTENSIN II TYPE 2 RECEPTOR STIMULATION IN THE ROSTRAL VENTROLATERAL MEDULLA: INTERACTION WITH GLUTAMATE AND GAMMA-AMINOBUTYRIC ACID

Event Abstract Back to Event HYPOTENSIVE RESPONSE TO ANGIOTENSIN II TYPE 2 RECEPTOR STIMULATION IN THE ROSTRAL VENTROLATERAL MEDULLA: INTERACTION WITH GLUTAMATE AND GAMMA-AMINOBUTYRIC ACID Laura LEGAT1*, Sofie Brouwers2, Ilse Smolders1 and Alain Dupont1, 2, 3 1 Vrije Universiteit Brussel, Department of Pharmaceutical Chemistry, Drug Analysis and Drug Information (FASC), Belgium 2 UZ Brussel, Department of Pharmacology and Cardiovascular Center, Belgium 3 UZ Brussel, Department of Clinical Pharmacology and Clinical Pharmacy (KFAR), Belgium Objectives Angiotensin II, glutamate and gamma-aminobutyric acid (GABA) interact within the rostral ventrolateral medulla and the paraventricular nucleus modulating the central regulation of blood pressure and sympathetic tone. Our aim was to assess the effects of local angiotensin II type 2 receptor stimulation within the rostral ventrolateral medulla and the paraventricular nucleus on neurotransmitter concentrations and mean arterial pressure. Methods In vivo microdialysis was used for measurement of extracellular glutamate and GABA levels and for local infusion of the angiotensin II type 2 receptor agonist Compound 21 in the rostral ventrolateral medulla and the paraventricular nucleus of conscious normotensive Wistar rats. The mean arterial pressure response to local Compound 21 was monitored with a pressure transducer under anaesthesia. Angiotensin II type 2 receptor selectivity was assessed using the angiotensin II type 2 receptor antagonist PD123319; the GABA(A) receptor antagonist bicuculline was used to assess the involvement of GABA(A) receptors. Results Infusion of C21 (0.05µg/µl/h) in the rostral ventrolateral medulla significantly increased GABA levels and lowered blood pressure. These effects were abolished by co-infusion with PD123319. No changes in neurotransmitter levels or effects on blood pressure were seen with PD123319 infusion alone. Co-infusion of bicuculline abolished the Compound 21 evoked decrease in mean arterial pressure. Infusion of Compound 21 within the paraventricular nucleus did not change extracellular neurotransmitter levels nor mean arterial pressure. Conclusion Selective stimulation of angiotensin II type 2 receptor within the rostral ventrolateral medulla by local Compound 21 infusion reduces blood pressure and increases local GABA levels in normotensive rats. This hypotensive response requires functional GABA(A) receptors, suggesting that GABAergic neurons are involved in the sympatho-inhibitory action underlying this hypotensive response. Keywords: Renin-angiotensin-system, angiotensin II type 2 receptors, compound 21, mean arterial pressure, rostral ventrolateral medualla, gamma-Aminobutyric Acid Conference: 12th National Congress of the Belgian Society for Neuroscience, Gent, Belgium, 22 May - 22 May, 2017. Presentation Type: Oral Presentation Topic: Sensory and Motor Systems Citation: LEGAT L, Brouwers S, Smolders I and Dupont A (2019). HYPOTENSIVE RESPONSE TO ANGIOTENSIN II TYPE 2 RECEPTOR STIMULATION IN THE ROSTRAL VENTROLATERAL MEDULLA: INTERACTION WITH GLUTAMATE AND GAMMA-AMINOBUTYRIC ACID. Front. Neurosci. Conference Abstract: 12th National Congress of the Belgian Society for Neuroscience. doi: 10.3389/conf.fnins.2017.94.00063 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 24 Apr 2017; Published Online: 25 Jan 2019. * Correspondence: Mrs. Laura LEGAT, Vrije Universiteit Brussel, Department of Pharmaceutical Chemistry, Drug Analysis and Drug Information (FASC), Jette, 1090, Belgium, laura_legat@hotmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Laura LEGAT Sofie Brouwers Ilse Smolders Alain Dupont Google Laura LEGAT Sofie Brouwers Ilse Smolders Alain Dupont Google Scholar Laura LEGAT Sofie Brouwers Ilse Smolders Alain Dupont PubMed Laura LEGAT Sofie Brouwers Ilse Smolders Alain Dupont Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Exploratory studies of some Mexican medicinal plants: Cardiovascular effects in rats with and without hypertension.

Papaveraceae Argemone mexicana L., Burseraceae Bursera simaruba (L.) Sarg., Acanthaceae Justicia spicigera Schltdl. and Selaginellaceae Selaginella lepidophylla (Hook. & Grev.) Spring., have been used in Mexican traditional medicine to treat hypertension. The objective of this study was to further characterize the cardiovascular effects of the methanol extracts of such plants. The medicinal plants were collected and taxonomically identified; the methanol extract of each explored plant were administrated to conscious and unconscious male Wistar rats with and without glucose-induced hypertension. The blood pressure (BP) and heart rate (HR) were evaluated before and after the extract administration. Vascular reactivity experiments were conducted in rat aortic rings obtained from rats with and without sugar-induced hypertension, a model widely used to study such effects with cardiovascular agents. After oral administration in normotensive conscious rats all tested extracts decreased the HR, such effect was only observed in hypertensive conscious rats after the administration of B. simaruba; only A. mexicana and B. simaruba decreased the BP after oral administration. All extracts administrated by intravenous injection diminished the mean arterial pressure. Dose-response curves to cumulative concentrations of all the extracts promote vascular relaxation in precontracted aortas from rats with and without sugar-induced hypertension. The present study indicated that B. simaruba is worthy of further investigation as a potential phytotherapeutic agent for treating hypertension.

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.

Abstract P617: Actions on the Splanchnic Venous System Contribute to 5-HT-induced Hypotension

Infusion of serotonin (5-hydroxytryptamine, 5-HT) into conscious normotensive and hypertensive rats causes a sustained reduction in systemic blood pressure. Imaging studies reveal that the blood pressure fall is closely associated with dilation of the large splanchnic veins (mesenteric, portal and abdominal vena cava), suggesting that active venodilation contributes to the fall in blood pressure. In fact, isolated splanchnic veins dilate directly to 5-HT via activation of the 5-HT 7 receptor, and a 5-HT 7 receptor antagonist prevents the 5-HT induced fall in blood pressure. To determine if the splanchnic venodilation caused by 5-HT is active or passive, anesthetized male Sprague Dawley rats were instrumented with arterial and venous lines for pressure measurements and 5-HT administration, respectively, while splanchnic veins were imaged using the Vevo® 2100 Ultrasound system. Measures were made relative to baselines measures. Within 5 minutes of infusion, 5-HT (25 ug/kg/min) caused an initial fall in portal vein pressure (~8-10% reduction) accompanied by dilation of the portal vein (~40% increase). No changes were seen in the dimensions or pressure of the abdominal vena cava at this time. Mean arterial blood pressure was reduced (&gt;40% reduction). All of these changes were prevented by pretreatment with the 5-HT 7 receptor antagonist SB269970. SB269970 during 5-HT infusion also caused an immediate reversal of changes in blood pressure and venous dimensions. Thus, active dilation of the pre-hepatic splanchnic venous system may be an early cause of 5-HT-induced hypotension. A more chronic experiment was performed in rats that were instrumented with a new dual channel radiotelemeter for concomitant measure of systemic and portal pressure in the conscious state. Within one hour after initiation of 5-HT infusion, portal venous pressure was elevated 38±0.2% above baseline (n=3) versus vehicle infused animals (4±0.3% above baseline; n=3), suggesting an action of 5-HT on intrahepatic venous resistance. Within 24 hours, portal pressure elevation resolved but blood pressure remained reduced. Collectively these data highlight the portal venous circulation as an important site of action for 5-HT in causing acute and chronic falls in systemic blood pressure.

Swimming Training Modulates Nitric Oxide-Glutamate Interaction in the Rostral Ventrolateral Medulla in Normotensive Conscious Rats.

We evaluated the effects of swimming training on nitric oxide (NO) modulation to glutamate microinjection within the rostral ventrolateral medulla (RVLM) in conscious freely moving rats. Male Wistar rats were submitted to exercise training (Tr) by swimming or kept sedentary (Sed) for 4 weeks. After the last training session, RVLM guide cannulas and arterial/venous catheters were chronically implanted. Arterial pressure (AP), heart rate (HR), and baroreflex control of HR (loading/unloading of baroreceptors) were recorded in conscious rats at rest. Pressor response to L-glutamate in the RVLM was compared before and after blockade of local nitric oxide (NO) production. In other Tr and Sed groups, brain was harvested for gene (qRT-PCR) and protein (immunohistochemistry) expression of NO synthase (NOS) isoforms and measurement of NO content (nitrite assay) within the RVLM. Trained rats exhibited resting bradycardia (average reduction of 9%), increased baroreflex gain (Tr: −4.41 ± 0.5 vs. Sed: −2.42 ± 0.31 b/min/mmHg), and unchanged resting MAP. The pressor response to glutamate was smaller in the Tr group (32 ± 4 vs. 53 ± 2 mmHg, p < 0.05); this difference disappeared after RVLM pretreatment with carboxy-PTIO (NO scavenger), Nw-Propyl-L-Arginine and L-NAME (NOS inhibitors). eNOS immunoreactivity observed mainly in RVLM capillaries was higher in Tr, but eNOS gene expression was reduced. nNOS gene and protein expression was slightly reduced (−29 and −9%, respectively, P > 0.05). Also, RVLM NO levels were significantly reduced in Tr (−63% vs. Sed). After microinjection of a NO-donor, the attenuated pressor response of L-glutamate in Tr group was restored. Data indicate that swimming training by decreasing RVLM NO availability and glutamatergic neurotransmission to locally administered glutamate may contribute to decreased sympathetic activity in trained subjects.

Cardiovascular effects induced by northeastern Brazilian red wine: Role of nitric oxide and redox sensitive pathways

Red wines have been shown to protect the vascular system by increasing the endothelial formation of nitric oxide (NO). This study investigated the vasoactive properties of an alcohol-free Cabernet-Sauvignon northeastern Brazilian red wine – RIOSOL (RSCS) extract. The polyphenolic-rich RSCS contained 4.2 mg GAE/L of polyphenols, and its major compounds included quercetin, myricetin and kaempferol. In normotensive conscious rats, RSCS produced hypotension and tachycardia, which were attenuated by the endothelial NO synthase inhibitor (eNOS), L-NAME. In addition, after 2 weeks of oral treatment, RSCS reduced arterial pressure in L-NAME-treated hypertensive rats. RSCS caused NO-mediated relaxations in phenylephrine contracted mesenteric artery rings, and induced the formation of NO and superoxide anions and a redox-sensitive phosphorylation of Akt and eNOS in cultured endothelial cells. In conclusion, the findings indicate that an alcohol-free lyophilized RSCS induced hypotension and endothelium-dependent vasorelaxation as a consequence of the activation of the Akt-eNOS-NO pathway in a redox-sensitive manner.

Anti-hypertensive Effects of Diminazene Aceturate: An Angiotensin- Converting Enzyme 2 Activator in Rats.

Previous studies have shown that activation of endogenous angiotensin-converting enzyme 2 (ACE2) results in various beneficial effects in the cardiovascular system. Recently, a new ACE2 activator, named diminazene aceturate (DIZE), was described. Here, we evaluated the actions of this compound in blood pressure (BP) and heart rate (HR) of conscious normotensive and hypertensive rats, as well as explored its mechanism of actions using isolated vessels. The renovascular model of hypertension was utilized. The participation of the Angiotensin-(1-7) receptor Mas and nitric oxide (NO) in the effects of DIZE was evaluated using A-779 and L-NAME, respectively. It was observed that DIZE caused a marked decrease in BP with a compensatory increase in HR in nornotensive rats. Accordingly, a significant reduction in the blood flow of the mesenteric bed was evidenced using intravital microscopy. Moreover, in rats with renovascular hypertension, DIZE caused a decrease in BP similar to the hypotensive effect induced by captopril. Importantly, this compound also prevented the development of cardiac hypertrophy induced by hypertension. The isolated vessels technique revealed that the vasodilator effects of DIZE were dependent on Mas activation and NO release. Thus, our findings demonstrated that DIZE reduces the BP of normotensinve and hypertensive rats possibly by a mechanism involving Mas and NO.

Butylidenephthalide antagonizes cromakalim-induced systolic pressure reduction in conscious normotensive rats.

BackgroundButylidenephthalide (Bdph), a main constituent of Ligusticum chuanxiong Hort., was reported to have selective antianginal effect without changing blood pressure in conscious rat. Recently, we have observed that Bdph antagonized cromakalim, an ATP-dependent K+ channel opener, in guinea-pig trachea. Thus, we were interested in investigating whether Bdph at the dose without changing blood pressure antagonized cromakalim-induced systolic pressure reduction in conscious rats.MethodsSystolic arterial pressures of conscious rats were determined by using the indirect tail-cuff method.ResultsBdph (30 mg/kg, i.p.) did not affect baseline systolic pressure in conscious normotensive and spontaneous hypertensive rats. Bdph (30 mg/kg, i.p.) also did not affect log dose–response curves of prazosin, clonidine and Bay K 8644, a Ca2+ channel activator, in normotensive rats. However, Bdph (30 mg/kg, i.p.) similar to 4-aminopyridine (4-AP, 0.4 mg/kg, i.p.), a K+ channel blocker, non-parallelly but surmountably, and partially similar to glibenclamide (GBC, 10 mg/kg, i.v.), an ATP-sensitive K+ channel blocker, surmountably but not parallelly rightward shifted the log dose-systolic pressure reduction curve of cromakalim, an ATP-sensitive K+ channel opener, in normotensive rats, respectively.DiscussionThe antagonistic effect of Bdph against cromakalim was similar to that of 4-AP, a K+ channel blocker of Kv1 family, and partially similar to that of GBC, an ATP-sensitive K+ channel blocker. Thus, Bdph may be a kind of K+ channel blockers, which have been reviewed to have a potential clinical use for Alzheimer disease. Indeed, Bdph has also been reported to reverse the deficits of inhibitory avoidance performance and improve memory in rats. Recently, 4-AP was reported to treat Episodic ataxia type 2 (EA2) which is a form of hereditary neurological disorder. Consistently, Bdph was recently reported to have antihyperglycemic activity in mice, since GBC is a powerful oral hypoglycemic drug.ConclusionsBdph similar to 4-AP and partially similar to GBC may block Kv1 family and ATP-sensitive K+ channels in conscious normotensive rats.

Acute and chronic role of nitric oxide, renin-angiotensin system and sympathetic nervous system in the modulation of calcium sensitization in Wistar rats.

Principal vasoactive systems - renin-angiotensin system (RAS), sympathetic nervous system (SNS), nitric oxide (NO) and prostanoids - exert their vascular effects through the changes in calcium levels and/or calcium sensitization. To estimate a possible modulation of calcium sensitization by the above vasoactive systems, we studied the influence of acute and chronic blockade of particular vasoactive systems on blood pressure (BP) changes elicited in conscious normotensive rats by acute dose-dependent administration of Rho-kinase inhibitor fasudil. Adult male chronically cannulated Wistar rats were used throughout this study. The acute inhibition of NO synthase (NOS) by L-NAME enhanced BP response to fasudil, the effect being considerably augmented in rats deprived of endogenous SNS. The acute inhibition of prostanoid synthesis by indomethacin modified BP response to fasudil less than the acute NOS inhibition. The chronic NOS inhibition caused moderate BP elevation and a more pronounced augmentation of fasudil-induced BP changes compared to the effect of acute NOS inhibition. This indicates both short-term and long-term NO-dependent attenuation of calcium sensitization. Long-term inhibition of RAS by captopril caused a significant attenuation of BP changes elicited by fasudil. In contrast, a long-term attenuation of SNS by chronic guanethidine treatment (in youth or adulthood) had no effect on BP response to fasudil, suggesting the absence of SNS does not affect calcium sensitization in vascular smooth muscle of normotensive rats. In conclusion, renin-angiotensin system contributes to the long-term increase of calcium sensitization and its effect is counterbalanced by nitric oxide which decreases calcium sensitization in Wistar rats.

Hypotensive and antihypertensive potential of 4-[(1-phenyl-1H-pyrazol-4-yl) methyl]1-piperazine carboxylic acid ethyl ester: A piperazine derivative

AimsClinical complaints on the first-line of cardiovascular medications make continuous search for new drugs a necessity. This study evaluated the cardiovascular effects and mechanism of 4-[(1-phenyl-1H-pyrazol-4-yl)methyl]1-piperazine carboxylic acid ethyl ester (LQFM008). Main methodsNormotensive male Wistar or spontaneously hypertensive rats (anesthetized or conscious) were used to evaluate the effect of LQFM008 on the mean arterial pressure (MAP), heart rate (HR), arterial blood flow (ABF), arterial vascular conductance (AVC), baroreflex effectiveness index (BI), systolic blood pressure (SBP), diastolic blood pressure (DBP) and vascular function. Key findingsIn anesthetized normotensive rats, LQFM008 (7.3, 14.3 or 28.6μmol/kg, iv) reduced MAP (−21.1±2.7; −23.9±4.7 or −32.4±8.3mmHg, respectively) and AVC (22%, 32% or 38%) in a dose-dependent manner. LQFM008 elicited a temporal reduction in the SBP and DBP without changes to the BI of conscious normotensive rats. In hypertensive rats, LQFM008 (7.3, 14.3 or 28.6μmol/kg, iv) reduced MAP (−2.3±2.6; −29.3±2.7 or −38.4±2.8mmHg, respectively) and increased HR (1.6±3.7; 15.4±4.9 or 25.5±6.2 bmp, respectively) in a dose-dependent manner. A week of oral administration of LQFM008 47.7μmol/kg elicited a temporal reduction in SBP of hypertensive rats. Pretreatments with atropine, WAY-100635 or L-NAME blocked the effect of LQFM008. In addition, LQFM008-induced endothelium-dependent vascular relaxation was inhibited by L-NAME. SignificanceOur findings showed hypotensive, antihypertensive and vasorelaxant effects of LQFM008 and suggest the participation of nitric oxide, 5-HT1A and muscarinic receptors.

Ser/thr phosphatases tonically attenuate the ERK-dependent pressor effect of ethanol in the rostral ventrolateral medulla in normotensive rats

We recently reported that microinjection of ethanol into the rostral ventrolateral medulla (RVLM) elicits modest increases in local extracellular signal-regulated kinase (ERK) and blood pressure (BP) in conscious normotensive rats. In this study, we tested the hypothesis that RVLM ser/thr phosphatases dampen the ERK-dependent pressor effect of ethanol in normotensive rats. We show that the pressor response elicited by intra-RVLM ethanol (10μg) was (i) abolished following local ERK inhibition with PD98059 (1μg) and (ii) associated with significant reduction in local phosphatase activity. Inhibition of the RVLM ser/thr phosphatase activity by okadaic acid (OKA, 0.4μg) or fostriecin (15pg) caused significant increases in blood pressure (BP) and potentiated the magnitude and duration of the pressor response as well as the phosphatase inhibition elicited by subsequent intra-RVLM administration of ethanol. Intra-RVLM acetaldehyde (2μg), the main metabolic product of ethanol, caused no changes in BP or RVLM phosphatase activity but it produced significant increases in BP and inhibition of local phosphatase activity in rats treated with OKA or fostriecin. Together, the RVLM phosphatase activity acts tonically to attenuate the ERK-dependent pressor effect of ethanol or acetaldehyde in normotensive rats.