Nitro L-arginine Research Articles

An investigation of the anti-hypertensive effect of mad honey and Rhododendron luteum sweet extract induced by N- ω -Nitro L-Arginine Methyl Ester (L-NAME) in rats

An investigation of the anti-hypertensive effect of mad honey and Rhododendron luteum sweet extract induced by N- ω -Nitro L-Arginine Methyl Ester (L-NAME) in rats

Black Seed (<i>Nigella sativa</i>) oil restores smoke or nicotine-induced vascular impairment via improvement in endothelium-dependent relaxation: role of nitric oxide synthase and voltage-sensitive potassium channels

Background: Despite the overwhelming evidence linking smoking and nicotine intake with vascular function impairments, the mechanisms involved and the possible ameliorative effect of black seed (Nigella sativa (NS)) oil administration are not clearly understood. This study sought to determine the involvement of nitric oxide synthase and voltage-sensitive potassium channels in the modulation of vascular reactivity in cigarette or nicotine-exposed rats treated with NS oil.
 Methods: Thirty male Sprague-Dawley rats were divided into 6 groups comprising vehicle control (Control), NS oil only (NS), Smoke only (SMK), Smoke + NS oil (SMKNS), Nicotine only (NCT) and Nicotine + NS oil (NCTNS). Animals were either passively exposed to cigarette smoke or nicotine vapour for 12 weeks, however, NS oil treatment commenced from 9th-12th week orally. At the end of the 12-week experimental period, vascular reactivity to norepinephrine (NE), acetylcholine (ACh) and sodium nitroprusside (SNP) were assessed with or without the presence of L-nitro-arginine (LNA) or 4-Amino-pyridine (4AP).
 Results: Percent contractile response to NE was higher (p < 0.01) while relaxation response to ACh was lower in the SMK and NCT (p < 0.05) groups. LNA-induced inhibition to ACh was significantly reduced in both SMK and NCT groups. 4AP-induced inhibition to ACh was significantly increased only in the NCT group. 4AP-induced inhibition to SNP was increased in SMK group. NS oil reduced only contractile response to NE in NCT group. It also significantly improved relaxation response to ACh as well as restored LNA-induced inhibition to ACh in the SMK and NCT groups. Interestingly, while NS oil reduced 4AP-induced inhibition in the NCT group, it reduced 4AP-induced inhibition to SNP in the SMK group.
 Conclusion: NS oil ameliorates vascular dysfunction by reducing contractile response in rats exposed to nicotine vapour while increasing endothelium-dependent relaxation as well as restoring differentially both LNA- and 4AP-induced inhibition in rats exposed to cigarette smoke and nicotine vapour.

Neural targets of the enteric dopaminergic system in regulating motility of rat proximal colon.

In isolated segments of the rat proximal colon, the dopamine reuptake inhibitor GBR 12909 (GBR) causes a dilatation, while the D1-like receptor antagonist SCH 23390 (SCH) induces a tonic constriction, suggesting that neurally released dopamine tonically stimulates enteric inhibitory efferent neurons. Here, the targets of the enteric dopaminergic neurons were investigated. Cannulated segments of rat proximal colon were bathed in physiological salt solution and luminally perfused with 0.9% saline, while all drugs were applied to the bath. Spatio-temporal maps of colonic motility were constructed from video recordings of peristaltic contractions, and the maximum diameter was measured as an index of colonic contractility. GBR (1μM)-induced dilatations of colonic segments were prevented by SCH (5μM), L-nitro arginine (L-NA; 100μM), a nitric oxide synthase inhibitor, or tetrodotoxin (0.6μM). In contrast, constrictions induced by a higher concentration of SCH (20μM) were unaffected by either L-NA or tetrodotoxin. The vasoactive intestinal peptide (VIP) receptor antagonist VIP10-28 (3μM) or P2Y1 receptor antagonist MRS 2500 (1μM) had no effect on either the GBR-induced dilatation or the SCH-induced constriction. In colonic segments that had been pretreated with 6-hydroxydopamine (100μM, 3h) to deplete enteric dopamine, GBR failed to increase the colonic diameter, while SCH was still capable of constricting colonic segments. Enteric dopaminergic neurons appear to project to nitrergic neurons to dilate the proximal colon by activating neuronal D1-like receptors. In addition, constitutively activated D1-like receptors expressed in cells yet to be determined may provide a tonic inhibition on colonic constrictions.

The role of feedback and modulation in determining temperature resiliency in the lobster cardiac nervous system.

Changes in ambient temperature affect all biological processes. However, these effects are process specific and often vary non-linearly. It is thus a non-trivial problem for neuronal circuits to maintain coordinated, functional output across a range of temperatures. The cardiac nervous systems in two species of decapod crustaceans, Homarus americanus and Cancer borealis, can maintain function across a wide but physiologically relevant temperature range. However, the processes that underlie temperature resilience in neuronal circuits and muscle systems are not fully understood. Here, we demonstrate that the non-isolated cardiac nervous system (i.e., the whole heart: neurons, effector organs, intrinsic feedback systems) in the American lobster, H. americanus, is more sensitive to warm temperatures than the isolated cardiac ganglion (CG) that controls the heartbeat. This was surprising as modulatory processes known to stabilize the output from the CG are absent when the ganglion is isolated. One source of inhibitory feedback in the intact cardiac neuromuscular system is nitric oxide (NO), which is released in response to heart contractions. We hypothesized that the greater temperature tolerance observed in the isolated CG is due to the absence of NO feedback. Here, we demonstrate that applying an NO donor to the isolated CG reduces its temperature tolerance. Similarly, we show that the NO synthase inhibitor L-nitroarginine (LNA) increases the temperature tolerance of the non-isolated nervous system. This is sufficient to explain differences in temperature tolerance between the isolated CG and the whole heart. However, in an intact lobster, the heart and CG are modulated by an array of endogenous peptides and hormones, many of which are positive regulators of the heartbeat. Many studies have demonstrated that excitatory modulators increase temperature resilience. However, this neuromuscular system is regulated by both excitatory and inhibitory peptide modulators. Perfusing SGRNFLRFamide, a FLRFamide-like peptide, through the heart increases the non-isolated nervous system's tolerance to high temperatures. In contrast, perfusing myosuppressin, a peptide that negatively regulates the heartbeat frequency, decreases the temperature tolerance. Our data suggest that, in this nervous system, positive regulators of neural output increase temperature tolerance of the neuromuscular system, while modulators that decrease neural output decrease temperature tolerance.

Exploring the possible mechanism involved in the anti-nociceptive effect of β-sitosterol: modulation of oxidative stress, nitric oxide and IL-6.

Β-sitosterol is a phytosterol, documented to possess various activities including protection againstinflammation, diabetes and Alzheimer's disease. The current investigation was designed to explore the analgesic potential of β-sitosterol and the possible molecular mechanism involved in the observed effect. β-sitosterol was administered at varying doses of 10, 20, and 40mg/kg before subjecting the mice to acetic acid and formalin challenges. The number of writhings in acetic acid and the number of flinchings and foot tappings were quantified in the formalin test. For mechanistic studies, substance P (cyclooxygenase-2 (COX-2) stimulator) and L-Nitro arginine methyl ester (L-NAME) (nitric oxide synthetases (NOS) inhibitor) and L-arginine (nitric oxide precursor) were administered before β-sitosterol treatment. β-sitosterol (10, 20, 40mg/kg) treatment significantly reduced acetic acid-induced writhings and ameliorated the formalin-induced inflammatory phase dose-dependently. Whereas, 40mg/kg dose of β-sitosterol abrogated the formalin-induced neurogenic phase. Substance-P abrogated the effect of β-sitosterol in both neurogenic and inflammatory phases. Whereas, L-arginine only abrogated the inflammatory phase. In biochemical analysis, β-sitosterol treatment reduced the level of interleukin-6 (IL-6), thiobarbituric acid reactive substances (TBARS) and increased the level of reduced glutathione (GSH). Furthermore, L-arginine and substance-P abrogated the GSH increasing and TBARS lowering effect of β-sitosterol (40mg/kg). Overall, the current study delineated that β-sitosterol may induce an anti-nociceptive effect via inhibiting the IL-6, oxidative stress, cyclo-oxygenase and nitric oxide.

Prophylactic Treatment with Hydrogen Sulphide Can Prevent Renal Ischemia-Reperfusion Injury in L-NAME Induced Hypertensive Rats with Cisplatin-Induced Acute Renal Failure.

(Background and Objectives): Renal ischemia perfusion injury is one of the major issues in kidney transplant. The aim of the study was to investigate the hypothesis that prophylactic treatment-with a hydrogen sulphide donor to an acute renal failure case of hypertensive rats-can minimize the ischemia reperfusion injury of the kidney which is beneficial for kidney transplant. To check this hypothesis, the present study was designed to investigate the effect of chronic administration of a hydrogen sulphide (H2S) donor and sodium hydrosulfide (NaHS) on nuclear factor kappa B (NF-kB) and inter cellular adhesion molecule-1 (ICAM-1) concentration in non-renal failure (NRF) and acute renal failure (ARF) rats in the ischemia-reperfusion injury (IRI) model of the kidney in both normotensive WKY and hypertensive rats (L-nitro arginine methyl ester (L-NAME-induced); (Materials and Methods): A total number of 48 Sprague-Dawley rats were recruited into eight groups each consisting of six animals. Each of these eight groups was used to measure systemic and renal parameters, H2S, antioxidant parameters in plasma, plasma concentration of NF-kB and ICAM-1 and renal cortical blood pressure. ARF was induced by single intraperitoneal (i.p.) cisplatin injection (5 mg/kg). Hypertension was induced by oral administration of L-NAME in drinking water for four weeks at 40 mg/kg/day. NaHS was administered (i.p) at 56 µmol/kg for five weeks while dL-propargylglycine (PAG), a H2S generation inhibitor, was administered as a single intra-peritoneal injection (50 mg/kg). An acute surgical experiment was performed for the induction of renal ischemia for 30 min by renal artery clamping followed by reperfusion for three hours; (Results): Chronic administration of NaHS attenuated the severity of ARF in both normotensive and hypertensive animals (L-NAME) along with lowering the blood pressure in hypertensive groups. NaHS improved the oxidative stress parameters such as total superoxide dismutase (T-SOD), glutathione (GSH) and reduced the malondialdehyde (MDA) concentration along with reduction of NF-kB and ICAM-1 following renal IRI; Conclusions: These findings demonstrate that H2S not only reduced the severity of cisplatin induced ARF but also reduced the severity of renal IRI by upregulating antioxidants along with decreased concentrations of NF-kB and ICAM-1 in normotensive and L-NAME induced hypertensive rats.

Ajuga bracteosa Exerts Antihypertensive Activity in l-NAME-Induced Hypertension Possibly through Modulation of Oxidative Stress, Proinflammatory Cytokines, and the Nitric Oxide/Cyclic Guanosine Monophosphate Pathway

Ajuga bracteosa has been used in traditional medicine to treat hypertension and other ailments. The present study has been designed to investigate the beneficial effects of A. bracteosa in l-nitro arginine methyl ester (l-NAME)-induced hypertensive rats. Hypertension was induced by intraperitoneal injection of l-NAME (185 μmol kg–1 i.p.). The aqueous methanol extract of A. bracteosa (AMEAB, 250 and 500 mg kg–1) and coumarin (30 and 70 mg kg–1) were administered orally from day 8 to day 35 of the study. In vivo antihypertensive activity was assessed by measuring the blood pressure using a PowerLab data system. The effects of the AMEAB and coumarin on nitric oxide (NO), cyclic guanosine monophosphate (cGMP), interleukin-6 (IL-6), the tumor necrosis factor (TNF-α), and oxidative stress markers were also assessed using kit methods. Phytochemical profiling of the AMEAB was carried out through high-performance liquid chromatography (HPLC) where quercetin, gallic acid, caffeic acid, vanillic acid, benzoic acid, syringic acid, p-coumaric acid, and ferulic acid were labeled as plant constituents including coumarin. The AMEAB and coumarin significantly reduced blood pressure at the tested doses of 500 and 70 mg kg–1, respectively. Serum levels of NO and cGMP were found to be significantly increased in AMEAB- and coumarin-treated groups when compared with only l-NAME-challenged rats. In addition, a marked decrease was noticed in the serum concentrations of proinflammatory cytokines (IL-6 and TNF-α) in AMEAB- and coumarin-treated rats. Moreover, in AMEAB- and coumarin-treated animals, a noticeable improvement was observed in the levels of antioxidant enzymes including catalase, superoxide dismutase, and malonaldehyde, and the total oxidant status when compared with those of only l-NAME-challenged rats. The data of real-time polymerase chain reaction (RT-PCR) experiments supported that the antihypertensive and anti-inflammatory activities of the AMEAB and coumarin are possibly mediated through modulation of endothelial nitric oxide synthase (eNOS), angiotensin-converting enzyme (ACE), nuclear factor (NF)-kB, and COX-2 gene expressions. This study concludes that A. bracteosa possesses an antihypertensive effect mediated through the modulation of the antioxidant, anti-inflammatory, and NO/cGMP pathways, thus providing a rationale to the antihypertensive use of A. bracteosa in traditional medicine.

Anti-cancer effect of in vivo inhibition of nitric oxide synthase in a rat model of breast cancer.

Increased expression of nitric oxide synthase (NOS) is associated with different cancers such as cervical, breast, lung, brain, and spinal cord. Inhibition of NOS activity has been suggested as potential tool to prevent breast cancer. The anti-tumor therapeutic effect of L-nitro arginine methyl ester (L-NAME), NOS inhibitor, using in vivo models is currently under investigation. We hypothesized that L-NAME will show an anti-tumor effect by delaying a progression of breast cancer via a modulation of cell death and proliferation, and angiogenesis. We used a novel model of anti-cancer treatment by the administration of L-NAME (30mg/kg in a day, intraperitoneal) injected every third day for five weeks to rat model of 7,12-dimethylbenz[a]anthracene (DMBA)-induced breast tumor. Concentrations of nitrite anions, polyamines, malondialdehyde, NH4+ levels, and arginase activity in the blood were decreased in DMBA + L-NAME-treated rats compared with DMBA rats. The mortality rates, tumor number, weight, and volume, as well as the histopathological grade of breast cancer were also significantly reduced. In addition, L-NAME treatment showed a delay in tumor formation, and in body weight compared with rats administrated only with DMBA. In conclusion, our data show that L-NAME is a promising anti-cancer agent to treat breast cancer, which can lead to development of anti-tumor therapeutic tools in future.

Prenatal Exposure to Methamphetamine Causes Vascular Dysfunction in Adult Male Rat Offspring.

Methamphetamine use during pregnancy can have negative consequences on the offspring. However, most studies investigating the impact of prenatal exposure to methamphetamine have focused on behavioral and neurological outcomes. Relatively little is known regarding the impact of prenatal methamphetamine on the adult cardiovascular system. This study investigated the impact of chronic fetal exposure to methamphetamine on vascular function in adult offspring. Pregnant female rats received daily saline or methamphetamine (5 mg/kg) injections starting on gestational day 1 and continuing until the pups were born. Vascular function was assessed in 5 month old offspring. Prenatal methamphetamine significantly decreased both the efficacy and potency of acetylcholine-induced relaxation in isolated male (but not female) aortas when perivascular adipose tissue (PVAT) remained intact. However, prenatal methamphetamine had no impact on acetylcholine-induced relaxation when PVAT was removed. Nitroprusside-induced relaxation of the aorta was unaffected by prenatal methamphetamine. Angiotensin II-induced contractile responses were significantly potentiated in male (but not female) aortas regardless of the presence of PVAT. This effect was reversed by L-nitro arginine methyl ester (L-NAME). Serotonin- and phenylephrine-induced contraction were unaffected by prenatal methamphetamine. Prenatal methamphetamine had no impact on acetylcholine-induced relaxation of third order mesenteric arteries and no effect on basal blood pressure. These data provide evidence that prenatal exposure to methamphetamine sex-dependently alters vasomotor function in the vasculature and may increase the risk of developing vascular disorders later in adult life.

Systemic administration of choline acetyltransferase decreases blood pressure in murine hypertension

Acetylcholine (ACh) decreases blood pressure by stimulating endothelium nitric oxide-dependent vasodilation in resistance arterioles. Normal plasma contains choline acetyltransferase (ChAT) and its biosynthetic product ACh at appreciable concentrations to potentially act upon the endothelium to affect blood pressure. Recently we discovered a T-cell subset expressing ChAT (TChAT), whereby genetic ablation of ChAT in these cells produces hypertension, indicating that production of ACh by TChAT regulates blood pressure. Accordingly, we reasoned that increasing systemic ChAT concentrations might induce vasodilation and reduce blood pressure. To evaluate this possibility, recombinant ChAT was administered intraperitoneally to mice having angiotensin II-induced hypertension. This intervention significantly and dose-dependently decreased mean arterial pressure. ChAT-mediated attenuation of blood pressure was reversed by administration of the nitric oxide synthesis blocker l-nitro arginine methyl ester, indicating ChAT administration decreases blood pressure by stimulating nitic oxide dependent vasodilation, consistent with an effect of ACh on the endothelium. To prolong the half life of circulating ChAT, the molecule was modified by covalently attaching repeating units of polyethylene glycol (PEG), resulting in enzymatically active PEG-ChAT. Administration of PEG-ChAT to hypertensive mice decreased mean arterial pressure with a longer response duration when compared to ChAT. Together these findings suggest further studies are warranted on the role of ChAT in hypertension.

Neural regulation of the contractility of nutrient artery in the guinea pig tibia.

Nutrient arteries provide the endosteal blood supply to maintain bone remodelling and energy metabolism. Here, we investigated the distribution and function of perivascular nerves in regulating the contractility of the tibial nutrient artery. Changes in artery diameter were measured using a video tracking system, while the perivascular innervation was investigated using fluorescence immunohistochemistry. Nerve-evoked phasic constrictions of nutrient arteries were suppressed by phentolamine (1μM), an α-adrenoceptor antagonist, guanethidine (10μM), a blocker of sympathetic transmission, or fluoxetine (10μM), a serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor. In arteries pretreated with guanethidine, residual nerve-evoked constrictions were abolished by a high concentration of propranolol (10μM) that is known to inhibit 5-HT receptors, or ketanserin (100nM), a 5-HT2 receptor antagonist, but not SB207216 (1μM), an antagonist of 5-HT3 and 5-HT4 receptors. Bath-applied 5-HT (100nM) induced arterial constriction that was suppressed by propranolol (10μM) or ketanserin (100nM). Nerve-evoked arterial constrictions were enhanced by spantide (1μM), a substance P (SP) receptor antagonist, or L-nitro arginine (L-NA; 100μM), an inhibitor of nitric oxide synthase (NOS). Immunohistochemistry revealed 5-HT-positive nerves running along the arteries that are distinct from perivascular sympathetic or substance P-positive primary afferent nerves. For the first time, functional serotonergic nerves are identified in the tibial nutrient artery of the guinea pig. Thus, it appears that tibial nutrient arterial calibre is regulated by the balance between sympathetic and serotonergic vasoconstrictor nerves and vasodilator afferent nerves that release substance P-stimulating endothelial nitric oxide (NO) release.

Renoprotective effects of the hydroethanolic extract of Senecio serratuloides against Nw-nitro L-arginine methyl ester-induced oxidative stress in wistar rats

Background: Oxidative stress is implicated in the pathogenesis of many diseases. Proper management of oxidative stress requires antioxidants from external sources to supplement that of the body. Plants are considered as a major source of antioxidants because of their natural origin and therapeutic benefits. Objectives: This study was aimed at investigating the renoprotective and antioxidant capacity of hydroethanolic extract of Senecio serratuloides (HESS). Materials and Methods: In vitro and ex vivo antioxidant capacity of the extract was investigated. Female Wistar rats were treated with Nw-nitro L-arginine methyl ester (L-NAME) (40 mg/kg) for 4 weeks and then cotreating with L-NAME (20 mg/kg) and extract (HESS150 or HESS300 mg/kg) for 2 weeks and finally with plant extract or normal saline only for 2 weeks making a total of 8 weeks. Twenty-four-hour urine samples were collected during the study, and at the end of the study; blood and kidneys were harvested for biochemical and histological assays. Results: HESS exhibited high antiradical activity against 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) radicals with IC50values of 0.1 and 0.4 mg/ml, respectively. HESS significantly (P

2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced aryl hydrocarbon receptor activation enhanced the suppressive function of mesenchymal stem cells against splenocyte proliferation

The immunosuppressive function of mesenchymal stem cells (MSCs) is well known. Aryl hydrocarbon receptor (AhR), a transcription factor of the bHLH/PAS family, is widely expressed in several cells and is involved in various physiological and pathological processes. Previously, we found that the expression of AhR was downregulated in MSCs isolated from mice with neutrophilic asthma and that the activation of AhR enhanced the function of MSCs to alleviate neutrophilic asthma. We hypothesized that AhR activation enhanced MSCs for their immunosuppressive function. We aimed to investigate whether AhR activation can augment the suppressive function of MSCs against splenocyte proliferation. We co-cultured MSCs or AhR-activated MSCs with splenocytes at different ratios. The results showed that AhR activation in MSCs upregulated the expression of inducible nitric oxide (iNOS), which promoted the production of nitric oxide (NO), thus enhancing the inhibitory effect on splenocyte proliferation. The NO donor S-nitroso-N-acetylpenicillamine also inhibited the proliferation of splenocytes, and the iNOS inhibitor N(G)-nitro L-arginine methyl ester and NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide partially reversed the immunosuppressive function. Our study indicates that the AhR activation of MSCs might have an important role in the regulation of splenocyte proliferation and might serve as a potential strategy for treating immune-related diseases.

Glutaminergic tonic action potentiate MPP+-induced hydroxyl radical production in rat striatum

The effect of glycine on 1-methyl-4-phenylpyridinium ion (MPP+)-induced hydroxyl radical (OH) formation in the extracellular fluid of rat striatum were investigated. Rats were anesthetized and sodium salicylate in Ringer's solution (0.5 nmol/μl/min) was infused through a microdialysis probe to detect the generation of OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) in rat striatum. MPP+ (5 mmol/L) produced an increase in OH formation. When glycine (1 mmol/L) was infused into the rat striatum through a microdialysis probe after MPP+ treatment, the marked in the level of 2,3-DHBA was observed in the brain dialysate. However, in the presence of MK-801 (100 μmol/L), a non competitive antagonist of N-methyl-D-aspartate (NMDA), glycine failed to increase the 2,3-DHBA formation by MPP+. When corresponding experiments were performed with nitro-L arginine (L-NNA) (1 mmol/L), a nitric oxide synthase (NOS) inhibitor, same result was obtained. These results suggest that MPP+-induced OH generation may modulated by glycine via NMDA receptor in rat striatum. This increase might be explained because of the presence of a glutaminergic tonic action

Exercise-induced sympathetic dilatation in arterioles of the guinea pig tibial periosteum.

Strength training induces not only muscle growth but also increased bone strength, a change that is expected to be associated with increased bone blood flow. However, the effects of exercise on contractile properties of bone microvascultaure have not been investigated. Once-a-week strength training with electrical muscle stimulation was applied unilaterally to tibialis anterior muscle of guinea pigs, while muscle force was measured from both legs to compare their muscle strength and endurance. After 10 weeks of training, changes in the arteriolar diameters of isolated periosteum taken from both trained and non-trained legs were measured using a video tracking system. Electrical field stimulation evoked a phasic constriction followed by a sustained dilatation in periosteal arterioles of trained legs, while triggering only vasoconstriction in the arterioles of non-trained legs. In trained leg arterioles, phentolamine, an α-adrenoceptor antagonist, inhibited both the constriction and dilatation. Prazosin, an α1-adrenoceptor antagonist, inhibited only the constriction, while yohimbine, α2-adrenoceptor antagonist, or l-nitro arginine (L-NA), a nitric oxide (NO) synthase inhibitor, inhibited the dilatation. In non-trained leg arterioles, phentolamine or prazosin largely suppressed the constriction, but failed to unmask any dilatation. Consistently, noradrenaline (NAd)-induced arteriolar constriction was enhanced and prolonged by L-NA in trained but not non-trained side arterioles. Thus, NAd released from sympathetic nerves appears to activate endothelial α2-adrenoceptors to release NO resulting in the sustained dilatation of periosteum arterioles from trained leg. The altered sympathetic vasomotor function would facilitate the blood supply to the bone and may contribute to the exercise-induced bone strength gain.

Activation of Large Conductance, Calcium-Activated Potassium Channels by Nitric Oxide Mediates Apelin-Induced Relaxation of Isolated Rat Coronary Arteries.

Apelin increases coronary blood flow, cardiac contractility, and cardiac output. Based on these favorable hemodynamic effects, apelin and apelin-like analogs are being developed for treating heart failure and related disorders; however, the molecular mechanisms underlying apelin-induced coronary vasodilation are unknown. This study aimed to elucidate the signaling pathways by which apelin causes smooth muscle relaxation in coronary arteries. Receptors for apelin (APJ receptors) were expressed in coronary arteries, as determined by Western blot and polymerase chain reaction analyses. Immunofluorescence imaging studies identified APJ receptors on endothelial and smooth muscle cells. In isolated endothelial cells, apelin caused an increase in 4,5-diaminofluorescein fluorescence that was abolished by nitro-l-arginine (NLA) and F13A (H-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Ala-OH), an APJ receptor antagonist, consistent with increased nitric oxide (NO) production. In arterial rings, apelin caused endothelium-dependent relaxations that were abolished by NLA, F13A, and iberiotoxin. Neither oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) nor DT-2, a protein kinase G inhibitor, had any effect on apelin-induced relaxations, and apelin itself had no effect on intracellular cGMP accumulation in coronary arteries. Patch-clamp studies in isolated smooth muscle cells demonstrated that the NO donors, diethyl amine NONOate and sodium nitroprusside, caused increases in large conductance, calcium-activated potassium channel (BKCa) currents, which were inhibited by iberiotoxin but not ODQ. Thus, apelin causes endothelium-dependent relaxation of coronary arteries by stimulating endothelial APJ receptors and releasing NO, which acts in a cGMP-independent manner and increases BKCa activity in the underlying smooth muscle cells. These results provide a mechanistic basis for apelin-induced coronary vasodilation and may provide guidance for the future development of novel apelin-like therapeutic agents.

Exercise (In)Tolerance in Sickle Cell Disease: Potential Disruptive Role of Free Hemoglobin on Skeletal Muscle Oxygen Delivery/Utilization Matching and Functional Capacity

Sickle cell disease (SCD) reduces exercise tolerance likely due to vascular and skeletal muscle abnormalities stemming from increased free hemoglobin (Hb, a known scavenger of nitric oxide). However, there has been little advancement in our understanding of the precise mechanisms responsible for the reduction in physical functionality. Therefore, the purpose of this investigation was 1) determine the degree by which exercise tolerance is impaired in a mouse model of SCD (BERK) and 2) examine the impact of free Hb on the skeletal muscle microvascular PO2 (PO2mv, the principal driving force that facilitates blood-muscle O2 flux) at rest and during muscle contractions in rats exposed to acutely elevated free [Hb]. We hypothesized that exercise capacity, as measured by the running speed/exercise duration relationship (critical speed, CS), would be lower in BERK relative to wild-type mice (WT) with a lower PO2mv observed during muscle contractions following Hb infusion. Twenty female mice (WT, n=10 and BERK, n=10) performed 4 constant-speed treadmill tests that resulted in fatigue within 1.5 to 20 min. Time to fatigue vs. treadmill speed were fit to a hyperbolic model to determine CS. PO2mv was measured (phosphorescence quenching) at rest and during 180 s of electrically induced (1-Hz) spinotrapezius muscle contractions during control, following free Hb infusion (Hb, 50 mg), and L-nitro arginine methyl ester superfusion (L-NAME, 1.5 mM) conditions in 9 rats. Speed and time to exhaustion for WT and BERK conformed to a hyperbolic relationship (WT: r2 = 0.93 ± 0.02, BERK: r2 = 0.97 ± 0.01, p>0.05). CS was significantly lower in BERK when compared to WT (WT: 33.1 ± 1.5, BERK: 25.2 ± 0.7 m/min, p<0.05). Following the onset of muscle contractions, Hb and L-NAME significantly increased the amplitude of the fall in PO2mv when compared to control, with no significant differences between Hb and L-NAME conditions (Δ1PO2mv: control: 9.5±0.7, Hb: 11.7±1, L-NAME 10.4±0.8 mmHg, p<0.05). The increased Δ1PO2mv resulted in a significantly lower PO2mv during the steady-state of muscle contractions in both Hb and L-NAME conditions, with no differences between Hb and L-NAME (PO2mv(steady-state): control: 24.1±0.9, Hb: 21.3±0.7, L-NAME: 19.6±1 mmHg, p<0.05). To summarize, exercise tolerance, as measured via CS, was significantly lower in BERK mice relative to WT. Furthermore, the lower PO2mv(steady-state) in Hb and L-NAME represents a compromised blood-myocyte O2 driving force during muscle contractions. Collectively, these data suggest that SCD impacts physical capacity via a disruption in the tight matching between oxygen delivery and utilization within the skeletal muscle and that this dysfunction could be mediated by a reduced nitric oxide bioavailability consequent of elevated free [Hb]. Support or Funding Information Funded by NIH (R01HL125642) to DCI and Colorado Nutrition and Obesity Research Center (P30DK048520) award to SKF. Mean percent PO2mv for the spinotrapezius muscle for control, Hb, and L-NAME conditions. Time “zero” represents the onset of electrically stimulated 1-hz twitch muscle contractions. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Potential effects of aliskiren on myocardial infarction on top of hypertension and heart failure in rats

Background Myocardial infarction (MI) is defined as an irreversible injury or subsequent necrosis of myocardial cells due to interruption of blood supply to a part of the heart. Heart failure (HF) occurs when the heart is unable to pump sufficiently to maintain blood flow to meet the body’s needs. Hypertension is a chronic medical condition in which the blood pressure in the arteries is elevated; it is said to be present when blood pressure values are at or above 140/90 mmHg. Aliskiren is a direct renin inhibitor indicated for the treatment of hypertension. Aim The present study was designed to evaluate the effects of aliskiren (50 mg/kg, intraperitoneally) on experimentally induced MI in hypertensive rats with HF. Materials and methods Model of MI: animals were classified into the following groups: normal control group, MI with no medication group (MI was induced by coronary artery ligation), MI l-nitro arginine methyl ester hydrochloride (l-NAME) group (hypertensive infarcted group), and aliskiren-treated MI l-NAME group. Model of HF: animals were classified into the following groups: normal control group, HF group (isoprenaline-induced HF), and aliskiren-treated HF group. Results Model of MI: aliskiren reduced blood pressure significantly when compared with the MI l-NAME group. It also improved cardiac enzymes (troponin and creatine phosphokinase-MB), ECG changes (heart rate and T-wave voltage), and infarction size when compared with the MI with no medication group and the MI l-NAME group (infarcted groups). Model of HF: it was found that aliskiren significantly reduced blood pressure when compared with the control group. It also significantly reduced heart rate and improved ejection fraction and histopathological changes of the heart compared with the HF group. Conclusion In this study, aliskiren had antihypertensive effects. It also could have a protective effect against MI and improve HF.

Antinociception induced by a novel α2A adrenergic receptor agonist in rodents acute and chronic pain models

The mechanisms and antinociceptive effects of a novel α2A adrenoceptor agonist, 3-(2-chloro-6-fluorobenzil)-imidazolinide-2,4-dione (PT-31) were investigated using animal models of acute and chronic pain. The effects of PT-31 on pain responses were examined using hot plate and formalin tests in mice and spinal nerve ligation (SNL)-induced hyperalgesia in rats. The effects of antagonists acting on α adrenoceptor were assessed to investigate the interaction of these pathways upon PT-31 induced antinociception. PT-31 effects on motor activity/skills and on hemodynamic parameters were also evaluated. PT-31 had dose-dependent antinociception effects on hot-plate and formalin-injection induced pain responses. Thermal hyperalgesia and mechanical allodynia were reduced following a 7 d treatment with PT-31 (1, 5, and 10mg/kg/d, p.o.), and those effects were attenuated by yohimbine (5mg/kg), atropine (2mg/kg), L-nitro arginine methyl ester (L-NAME; 30mg/kg), or naloxone (2mg/kg). In contrast to clonidine, PT-31 did not have locomotor or hemodynamic effects in rats. The present results suggest that PT-31 represents a candidate for pain treatment with advantages over clonidine, namely no locomotor or hemodynamic impairments.

Antihypertensive and antioxidant activity of Cassytha filiformis L.: A correlative study

ObjectiveTo study the blood pressure lowering effect of Cassytha filiformis extract in animal models of hypertension and its correlation with the antioxidant activity. MethodsMale Sprague–Dawley rats were divided into two groups: endocrine hypertension (HTN group) that received a combination of prednisone and salt for two weeks and oxidative stress-associated hypertension (HTN-OS group) that received additional induction of l-Nitro Arginine Methyl Esther (l-NAME) for two days. Each group was subdivided into 4 and treated intravenously with the extract 5; 10; and 20 mg/kg, and vehicle control. The systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) were recorded. The blood was taken before and at the end of recording for the measurement of serum concentration of nitric oxide (NO). The changes of blood pressure were analyzed by two-way ANOVA while its correlation with NO concentration was analyzed by Pearson's Correlation. ResultsThe study showed a significant antihypertensive effect of the extract as compared with control group (P < 0.05) in both hypertensive models. Extract in the dose of 5 mg/kg showed the best blood pressure lowering effect. However, the correlation analysis did not show an association between NO increase and blood pressure lowering effect (P > 0.05). ConclusionsThe study concludes that C. filiformis extract in the dose of 5 mg/kg exhibits the best blood pressure lowering effect in both animal models. Antihypertensive activity of the extract is not correlated with its antioxidant effect.