Dilatation Of Middle Cerebral Artery Research Articles

Role of the endothelial reverse mode sodium-calcium exchanger in the dilation of the rat middle cerebral artery during hypoosmotic hyponatremia

A decrease in serum sodium ion concentration below 135 mmol L−1 is usually accompanied by a decrease in plasma osmolality (hypoosmotic hyponatremia) and leads to the disorder of intracranial homeostasis mainly due to cellular swelling. Recently, using an in vitro model of hypoosmotic hyponatremia, we have found that a decrease in sodium ion concentration in the perfusate to 121 mmol L−1 relaxes the isolated rat middle cerebral artery (MCA). The aim of the present study was to explore the mechanism responsible for this relaxation. Isolated, pressurized, and perfused MCAs placed in a vessel chamber were subjected to a decrease in sodium ion concentration to 121 mmol L−1. Changes in the diameter of the vessels were monitored with a video camera. The removal of the endothelium and inhibition of nitric oxide-dependent signaling or the reverse mode sodium-calcium exchanger (NCX) were used to study the mechanism of the dilation of the vessel during hyponatremia. The dilation of the MCA (19 ± 5%, p < 0.005) in a low-sodium buffer was absent after removal of the endothelium or administration of the inhibitor of the reverse mode of sodium-calcium exchange and was reversed to constriction after the inhibition of nitric oxide (NO)/cGMP signaling. The dilation of the middle cerebral artery of the rat in a 121 mmol L−1 Na+ buffer depends on NO signaling and reverse mode of sodium-calcium exchange. These results suggest that constriction of large cerebral arteries with impaired NO-dependent signaling may be observed in response to hypoosmotic hyponatremia.

Can Myogenic Tone Protect Endothelial Function? Integrating Myogenic Activation and Dilator Reactivity for Cerebral Resistance Arteries in Metabolic Disease

The obese Zucker rat (OZR) manifests multiple risk factors for impaired cerebrovascular function, including hypertension and insulin resistance although how they combine to produce integrated vascular function is unclear. As studies have suggested that myogenic activation (MA) severity for middle cerebral arteries (MCAs) may be proportional to hypertension severity, we hypothesized that MA will negatively correlate with dilator reactivity in OZR. MA of MCA from OZR was divided into low, medium, and high based on the slope of MA, while MCA reactivity and vascular metabolite bioavailability were assessed in all groups. Endothelium-dependent dilation of MCA in OZR was attenuated and correlated with the MA slope. Treatment of OZR MCA with TEMPOL (antioxidant) improved dilation in low or medium MA groups, but had less impact on high MA. Alternatively, treatment with gadolinium to normalize MA in OZR had reduced impact on dilator reactivity in MCA from low and medium MA groups, but improved responses in the high group. Treatment with both agents resulted in dilator responses that were comparable across all groups. These results suggest that, under conditions with stronger MA, endothelial function may receive some protection despite the environment, potentially from the ability of MCA to reduce wall tension despite increased pressure.

Endothelium-dependent impairments to cerebral vascular reactivity with type 2 diabetes mellitus in the Goto-Kakizaki rat.

Type 2 diabetes mellitus (T2DM) is a prevalent pathology associated with elevated cerebrovascular disease risk. We determined wall mechanics and vascular reactivity in ex vivo middle cerebral arteries (MCA) from male Goto-Kakizaki rats (GK; ~17 wk old) versus control Wistar Kyoto rats (WKY) to test the hypothesis that the diabetic environment in GK, in the absence of obesity and other comorbidities, leads to endothelial dysfunction and impaired vascular tone regulation. Dilation of MCA following challenge with acetylcholine and hypoxia was blunted in MCA from GK versus WKY, due to lower nitric oxide bioavailability and altered arachidonic acid metabolism, whereas myogenic activation and constrictor responses to serotonin were unchanged. MCA wall distensibility and cross-sectional area were not different between GK and WKY, suggesting that wall mechanics were unchanged at this age, supported by the determination that MCA dilation to sodium nitroprusside was also intact. With the use of ex vivo aortic rings as a bioassay, altered vascular reactivity determined in MCA was paralleled by relaxation responses in artery segments from GK, whereas measurements of vasoactive metabolite production indicated a loss of nitric oxide and prostacyclin bioavailability and an increased thromboxane A2 production with both methacholine challenge and hypoxia. These results suggest that endothelium-dependent dilator reactivity of MCA in GK is impaired with T2DM, and that this impairment is associated with the genesis of a prooxidant/pro-inflammatory condition with diabetes mellitus. The restriction of vascular impairments to endothelial function only, at this age and development, provide insight into the severity of multimorbid conditions of which T2DM is only one constituent.

Mas1 Receptor Knockout Rats as a Novel Model to Study Vascular Function in Salt‐Sensitive Hypertension

Hypertension is a critical risk factor for coronary and peripheral arterial disease, stroke and heart failure. It has been shown that activation of the Mas1 receptor (Mas1R) for angiotensin (1–7) [Ang (1–7)] has potent beneficial effects to offset the impaired vascular relaxation caused by increased oxidative stress, reduced nitric oxide (NO) availability, and down regulation of antioxidant defense mechanisms that occur during salt‐induced angiotensin II (ANG II) suppression. The recent development of a Mas 1R‐knockout rat (Mas 1R KO) in the Dahl salt sensitive (SS) genetic background is a crucial development, because this genetic model will allow for more detailed studies of Mas 1R function at the whole animal, molecular, and cellular level in salt‐sensitive rats. The aim of this study was to provide initial phenotyping of vascular responses in middle cerebral arteries (MCA) of wild type (WT) and Mas1R KO rats. Mas 1R KO− and WT rats were maintained on a low salt (LS; 0.4 % NaCl) diet to evaluate endothelial function without elevated blood pressure. MCA were isolated to assess vascular function ex vivo using the endothelium‐dependent vasodilator acetylcholine (ACh), exogenously added Ang (1–7), the non‐peptide Ang‐(1–7) mimic AVE 0991, and the NO donor sodium nitroprusside (SNP). ACh induced a concentration‐dependent dilation in isolated arteries from Mas 1R WT rats but not in Mas 1R KO arteries (p&lt;0.05). Arteries stimulated with Ang (1–7) and AVE 0991 exhibited a concentration‐dependent vasodilation in Mas 1R WT but not in Mas 1R KO rats. However, endothelium‐independent vessel relaxation by SNP was unaltered in KO vessels compared to WT controls. The vasodilator effect of Ang (1–7) and AVE 0991 were eliminated by the Ang (1–7) receptor antagonist A779 and by inhibition of NO synthase with L‐NAME. Dilation of MCA in response to the AT2 receptor agonist cGP42112A was unaltered in Mas 1R KO rats. Our results indicate that Mas 1R activation has an important role in maintaining endothelial cell function in WT rats. Use of the novel Mas 1R KO genetic rat model provides a powerful tool to investigate Mas 1R functions at the molecular and cellular level. Further study of the mechanisms by which Mas1 receptors induce protective effects in the endothelium will be important since Mas 1R receptor analogs such as AVE 0991 and Ang (1–7) may offer a potentially novel therapeutic strategy for the management of hypertension.Support or Funding InformationThis work was supported in part by grants: R21‐OD024781‐01, R01‐HL128242 and T32‐GM089586 from the National Institutes of Health, Bethesda, MDThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vascular Protection of Hydrogen Sulfide on Cerebral Ischemia/Reperfusion Injury in Rats.

This study was undertaken to demonstrate the vascular protection of exogenous and endogenous hydrogen sulfide (H2S) on cerebral ischemia/reperfusion (I/R) injury. The effect of H2S on cerebrovascular dysfunction in middle cerebral artery (MCA) and neuronal damage were measured after cerebral I/R induced by transient middle cerebral artery occlusion (MCAO) in cystathionine c-lyase (CSE) knockdown and wild-type rats. The effect of sodium hydrosulfide (NaHS, donor of exogenous H2S), L-cysteine (L-Cys, substrate of endogenous H2S), and endothelium cells on the responses of isolated MCA derived from non-ischemic rats was also evaluated to assess the underlying mechanism of H2S-mediate cerebral vasodilation. The results revealed that the contraction and dilation of MCA profoundly decreased after cerebral I/R. The vascular dysfunction became more grievous in CSE knockdown rats than in wild-type rats. Interestingly, this vascular dysfunction was significantly alleviated by NaHS supplementation. Moreover, both NaHS and L-cysteine could induce remarkable relaxation in the isolated MCA, which was eliminated by co-application of potassium channel blockers ChTx and Apamin, or endothelial removal. By contrast, adding endothelium cells cultured in vitro together with ACh into the luminal perfusate could mimic non-NO and non-PGI2 relaxation in endothelium-denuded MCA, once CSE was knocked down from endothelium cells, and its effect on vasorelaxation was abolished. Furthermore, the indexes of neuronal injury were measured after cerebral I/R to confirm the neuroprotection of H2S, and we found that the neurological scores, cerebral infarction volume, brain water content, malondialdehyde content, and serum lactate dehydrogenase activity (a marker of cellular membrane integrity) were significantly higher in CSE knockdown rats than in normal control rats. It is not surprising that NaHS could alleviate the cerebral injury. These findings revealed that H2S has a protective effect on cerebral I/R injury via its upregulation of the endothelium-dependent contraction and dilation function of cerebral vessels, which may be related to activating potassium channel.

High salt intake shifts the mechanisms of flow-induced dilation in the middle cerebral arteries of Sprague-Dawley rats.

The goal of the present study was to examine the effect of 1 wk of high salt (HS) intake and the role of oxidative stress in changing the mechanisms of flow-induced dilation (FID) in isolated pressurized middle cerebral arteries of male Sprague-Dawley rats ( n = 15-16 rats/group). Reduced FID in the HS group was restored by intake of the superoxide scavenger tempol (HS + tempol in vivo group). The nitric oxide (NO) synthase inhibitor Nω-nitro-l-arginine methyl ester, cyclooxygenase inhibitor indomethacin, and selective inhibitor of microsomal cytochrome P-450 epoxidase activity N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide significantly reduced FID in the low salt diet-fed group, whereas FID in the HS group was mediated by NO only. Cyclooxygenase-2 mRNA (but not protein) expression was decreased in the HS and HS + tempol in vivo groups. Hypoxia-inducible factor-1α and VEGF protein levels were increased in the HS group but decreased in the HS + tempol in vivo group. Assessment by direct fluorescence of middle cerebral arteries under flow revealed significantly reduced vascular NO levels and increased superoxide/reactive oxygen species levels in the HS group. These results suggest that HS intake impairs FID and changes FID mechanisms to entirely NO dependent, in contrast to the low-salt diet-fed group, where FID is NO, prostanoid, and epoxyeicosatrienoic acid dependent. These changes were accompanied by increased lipid peroxidation products in the plasma of HS diet-fed rats, increased vascular superoxide/reactive oxygen species levels, and decreased NO levels, together with increased expression of hypoxia-inducible factor-1α and VEGF. NEW & NOTEWORTHY High-salt (HS) diet changes the mechanisms of flow-induced dilation in rat middle cerebral arteries from a combination of nitric oxide-, prostanoid-, and epoxyeicosatrienoic acid-dependent mechanisms to, albeit reduced, a solely nitric oxide-dependent dilation. In vivo reactive oxygen species scavenging restores flow-induced dilation in HS diet-fed rats and ameliorates HS-induced increases in the transcription factor hypoxia-inducible factor-1α and expression of its downstream target genes.

Traumatic brain injury impairs myogenic constriction of cerebral arteries: role of mitochondria‐derived H2O2, TRPV4 and calcium‐activated potassium channels

Traumatic brain injury (TBI) impairs pressure‐induced myogenic constriction of cerebral arteries, which contributes to TBI‐related autoregulatory dysfunction and the development of secondary brain injury. TBI has been shown to lead to mitochondrial oxidative stress in cerebral vessels, which likely contributes to secondary brain injury, as well. We tested the hypothesis that TBI‐induced mitochondrial oxidative stress contributes to the impaired myogenic response of cerebral arteries after TBI and aimed to establish the underlying mechanisms. We induced traumatic brain injury in WKY rats using the weight‐drop technique, and 24 hours after severe TBI we found that myogenic responses of isolated middle cerebral arteries (MCAs) of TBI rats were blunted compared to control. The impaired myogenic responses of MCAs were restored after inhibiting mitochondrial oxidative stress (mitoTEMPO), eliminating H2O2 (PEG catalase) and blocking large‐conductance calcium‐activated potassium (BKCa) channels and transient receptor activated vanilloid channel 4 (TRPV4). We also found that H2O2‐induced dilation of MCAs involves the activation of BKCa and TRPV4 channels, and that H2O2‐induced BK currents on vascular smooth muscle cells depend on the activation of TRPV4 channels. Our results suggest that after TBI excessive mitochondria‐derived H2O2 activates BKCa channels via TRPV4 channel activation in the cerebrovascular wall, which diminishes pressure‐induced constriction of cerebral vessels. Future studies should elucidate the potential of inhibiting these vascular pathways to restore autoregulatory function after TBI in order to prevent TBI‐related secondary brain damage in patients suffered traumatic brain injury.Support or Funding InformationThis work was supported by grants from the Marie Curie Actions SMARTER 7th Framework Program of the European Union 606998 (to NSz and AK), the Hungarian Academy of Sciences (the Bolyai Research Scholarship BO/00634/15 to PT), the Hungarian Brain Research Program (Grant No. KTIA_13_NAP‐A‐II/8 to PT, ECz and AB), National Center for Complementary and Alternative Medicine (R01‐AT006526 to ZU) and the Hungarian Scientific Research Fund (K108444 to AK).

Rebuttal from Ryan L. Hoiland and Philip N. Ainslie.

Brothers & Zhang (2016) provide a relevant CrossTalk discussion on the measurement of middle cerebral artery (MCA) diameter during alterations in arterial blood pressure (ABP) and gases. While in support of a constant MCA diameter, they nonetheless judiciously acknowledge that several previous studies indicating a constant MCA diameter, specifically during alterations in arterial blood gases, are confounded by subject co-morbidities, anesthesia, and/or suffer from poor resolution (1.5 T MRI) (Schreiber et al. 2000; Serrador et al. 2000). They speculate that elevations in ABP and the associated autoregulatory response concurrent to hypercapnia may explain the increases in diameter reported by the more recent and higher resolution MRI studies (3 and 7 T) assessing MCA diameter (Verbree et al. 2014; Coverdale et al. 2014). The rationale for this hypothesis is unclear as the available data in humans indicate an increase in ABP will increase cerebral vascular resistance in large cerebral arteries (Liu et al. 2013; Warnert et al. 2016). Collectively, these findings indicate that any engagement of autoregulatory mechanisms would more likely lead to an underestimation of vasodilatation, not overestimation. In their discussion of arterial blood gases, Brothers & Zhang fail to discuss the potential for hypoxia-induced vasomotion of the MCA. Previous study has indicated MCA dilatation in hypoxia (Wilson et al. 2011), in addition to more recent evidence that continues to highlight a tendency for increased MCA diameter (Sagoo et al. 2016). Overall there is a strong body of data supporting hypoxia-induced dilatation at the level of the MCA. It is noted by Brothers & Zhang that the study by Serrador et al. (2000) provides insight into MCA diameter during mild hypotension; however, a statistical change in BP did not occur during their simulated orthostasis trial (see Table 2 in Serrador et al. 2000). This renders the study by Giller et al. (1993) the only one to date that has directly imaged MCA diameter during alterations in ABP. Thus, while it remains difficult to definitively conclude the effect of ABP on MCA diameter, a large body of evidence now supports the notion that MCA diameter does change during alterations in arterial blood gases. Although we acknowledge that much utility still exists in the employment of transcranial Doppler ultrasound, we encourage the complimentary addition of multi-modal imaging to provide important new insight into cerebrovascular regulation in humans. Readers are invited to give their views on this and the accompanying CrossTalk articles in this issue by submitting a brief (250 word) comment. Comments may be submitted up to 6 weeks after publication of the article, at which point the discussion will close and the CrossTalk authors will be invited to submit a ‘Last Word’. Please email your comment, including a title and a declaration of interest, to jphysiol@physoc.org. Comments will be moderated and accepted comments will be published online only as ‘supporting information’ to the original debate articles once discussion has closed. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. The authors declare no conflict of interest, financial or otherwise. Both authors have approved the final version of the manuscript and agree to be accountable for all aspects of the work. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed.

Salt‐Induced Oxidant Stress in Sprague‐Dawley (S‐D) Rats with a Deletion Mutation of the Nrf2 Gene

This study assessed the role of the master antioxidant and cell protective transcription factor nuclear factor (erythroid-derived 2)-like-2 (NRF2) in mutant rats having a 41 base pair deletion in the first exon of the Nrf2 gene including the start codon for NRF2. The deletion was produced using TALEN technology and verified by PCR and immunohistochemistry. Expression of mRNA for the NRF2-regulated indicator enzymes catalase, heme oxygenase-1 (HO-1), manganese superoxide dismutase (SOD2), and glutathione reductase (GSR) was significantly lower in livers of Nrf2 mutant rats fed high salt (HS; 4% NaCl) diet for 2 weeks vs. wild type controls. Acetylcholine (ACh)-induced dilation of middle cerebral arteries (MCA) was similar in Nrf2 mutant rats and wild type controls fed low salt (0.4% NaCl) diet and eliminated by short term (3 days) HS diet in both strains. Low dose angiotensin II (ANG II) infusion (100 ng/kg/min, s.c.) restored ACh-induced dilation in MCA of HS-fed wild type rats but not in MCA of HS-fed Nrf2 mutantrats. In S-D rats fed HS diet, ANG II infusion increased NRF2/KEAP1 ratio and prevented the down regulation of mRNA for catalase, SOD2, HO-1, and GSR. These results indicate that downregulation of the NRF2 system by salt-induced ANG II suppression plays an important role in the vascular dysfunction associated with HS diet. [NIH #2R1R21OD018309-01 and #2R56HL065289-13].

The cytokines TNF, MCP‐1 and CINC‐1 mediate diminished dilation of middle cerebral artery after ischemic stroke in rats (1068.2)

The level of inflammatory cytokines TNF, Monocyte Chemoattractant Protein (MCP‐1) and Cytokine‐Induced Neutrophil Chemoattractant (CINC‐1) is elevated after ischemic stroke (IS). The vasomotor effects of TNF, MCP‐1 and CINC‐1 on cerebral arteries have not yet been fully elucidated after IS. We aimed to evaluate the direct effect of these cytokines on MCA diameter under normal conditions and also after IS. In isolated, pressurized middle cerebral arteries (MCA) of normal Wistar rats, TNF, CINC‐1 (10‐14 ‐ 10‐11 M) and MCP‐1 (10‐16 ‐ 10‐13 M) elicited vasodilation (max: 26±3%, 21±4% and 28±7%, respectively), which was enhanced after endothelial denudation. In rats with transient MCA occlusion, a well‐known model of IS (90 min occlusion and 48 reperfusion) we observed a significantly reduced dilation to TNF, MCP‐1 and CINC‐1 in the ipsilateral MCA, whereas constriction of contralateral MCA was seen in response to TNF and CINC‐1. We also found reduced dilations of both ipsilateral and contralateral MCA in response to bradykinin and serotonin, but not to the NO‐donor, sodium nitroprusside in IS rats. Thus, TNF, MCP‐1 and CINC‐1 elicit endothelium‐independent vasodilation in MCA, which is significantly reduced after IS. Our data suggest reduced dilator or even enhanced constrictor signaling from damaged endothelium and indicate important role for these cytokines in regulating cerebral perfusion after IS.Grant Funding Source: Supported by NIH HL104126

Remodeling and impaired dilation in middle cerebral arteries from Deoxycorticosterone acetate (DOCA)‐salt rats

Genetic hypertension causes inward remodeling and impaired dilation in the middle cerebral artery (MCA). DOCA‐salt rats are widely used model of hypertension, yet few studies have been performed on their cerebral arteries. We hypothesized that MCAs from DOCA‐salt hypertensive rats will have a reduced lumen diameter and impaired endothelium dependent dilation. Male Sprague‐Dawley rats had uninephrectomy, and received either DOCA (150mg/kg) and salt water (1% NaCl and 0.2% KCl) or tap water. MCAs were studied by pressure myography. Data are mean±SEM, SHAM vs DOCA. DOCA showed impaired dilation to 10 μM ADP (change from baseline: 41.2±5.2 vs 24.7±4.7%, p&lt; 0.05, ANOVA). Lumen diameter was reduced (295±18 vs 343±13 μm at 80 mmHg, p &lt;0.05, ANOVA) in the DOCA rats. Interestingly the wall/lumen ratio (0.06±0.02 vs 0.07±0.01 at 80 mmHg, p&gt;;0.05, ANOVA) did not change. These data suggest the MCAs from DOCA rats may exhibit inward hypotrophic remodeling. These data are contrary to the inward hypertrophic remodeling observed in MCAs from genetically hypertensive rats and imply that the mechanism of remodeling in DOCA‐salt rats may be different.

Introgression of Brown Norway CYP4A genes on to the Dahl salt-sensitive background restores vascular function in SS-5BN consomic rats

The present study tested the hypothesis that the Dahl SS (salt-sensitive) rat has vascular dysfunction due, in part, to the up-regulation of the CYP4A/20-HETE (cytochrome P450 ω-hydroxylase 4A)/20-hydroxyeicosatetraenoic acid) system. To assess the role of vascular 20-HETE, SS rats were compared with SS-5(BN) consomic rats, carrying CYP4A alleles on chromosome 5 from the normotensive BN (Brown Norway) introgressed on to the SS genetic background. Cerebral arteries from SS-5(BN) rats had less CYP4A protein than arteries from SS rats fed either NS (normal-salt, 0.4% NaCl) or HS (high-salt, 4.0% NaCl) diet. ACh (acetylcholine)-induced dilation of MCAs (middle cerebral arteries) from SS and SS-5(BN) rats was present in SS-5(BN) rats fed on either an NS or HS diet, but absent in SS rats. In SS rats fed on either diet, ACh-induced dilation was restored by acute treatment with the CYP4A inhibitor DDMS (N-methyl-sulfonyl-12,12-dibromododec-11-enamide) or the 20-HETE antagonist 20-HEDE [20-hydroxyeicosa-6(Z),15(Z)-dienoic acid]. The restored response to ACh in DDMS-treated SS rats was inhibited by L-NAME (N(G)nitro-L-arginine methyl ester) and unaffected by indomethacin or MS-PPOH [N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide]. Vascular relaxation responses to the NO donor C(5)FeN(6)Na(2)O were intact in both SS and SS-5(BN) rats and unaffected by the acute addition of DDMS, indicating that the vascular dysfunction of the SS rat is due to a reduced bioavailability of NO instead of failure of the VSMCs (vascular smooth muscle cells) to respond to the vasodilator. Superoxide levels in cerebral arteries of SS-5(BN) rats [evaluated semi-quantitatively by DHE (dihydroethidium) fluorescence] were lower than those in the arteries of SS rats. These findings indicate that SS rats have an up-regulation of the CYP4A/20-HETE pathway resulting in elevated ROS (reactive oxygen species) and reduced NO bioavailability causing vascular dysfunction.

Abstract 661: Genetic Interference with Peroxisome Proliferator-Activated Receptor Gamma in Vascular Muscle Impairs Cerebrovascular Responses to Nitric Oxide and Enhances Myogenic Tone Via a Rho Kinase-Dependent Mechanism

Cerebral arteries are important resistance vessels in brain and play a crucial role in regulating cerebral blood flow. Nitric oxide (NO) plays a major role in the cerebral circulation influencing vascular structure and blood flow, mediating endothelium-dependent vasodilation, and contributing to neurovascular coupling. Peroxisome proliferator-activated receptor-gamma (PPARγ) is a transcription factor that may play a protective role in the vasculature by enhancing NO signaling and inhibiting increases in vascular tone. We tested whether cell-specific interference with PPARγ in smooth muscle would alter responses to NO and increase myogenic tone in cerebral arteries. We studied mice expressing either a dominant negative mutation of human PPARγ (P467L) or increased expression of WT PPARγ (S-WT) in smooth muscle (S-P467L). In basilar arteries, vasodilation to nitroprusside (NO donor) was markedly impaired in S-P467L compared with S-WT or non-transgenic mice (NT) (e.g. 1 μM nitroprusside: NT, 60±6% vs. S-WT, 63±2% vs. S-P467L, 16±3%, n=6-11). As PPARγ may suppress rho kinase signaling, we examined its role in regulating responses to NO. Impaired vasodilation to nitroprusside in S-P467L mice were restored to normal by an inhibitor of rho kinase (Y27632, 3 μM). Angiotensin II (Ang II) activates rho kinase via AT1 receptors. As AT1-mediated effects may also be suppressed by PPARγ, we examined effects of an AT1 receptor antagonist (losartan). Losartan (1 μM) completely inhibited vasoconstriction to Ang II and increased responses to nitroprusside to ∼70% of normal in S-P467L mice. In response to intraluminal pressure (75 mmHg), middle cerebral arteries (MCA) from S-P467L mice constricted 31±4% compared with 9±2% for NT (n=7-8). Dilation of MCA from S-P467L mice to acetylcholine was significantly impaired compared with controls, whereas dilation to papaverine was similar between genotypes. Treatment of the MCA from S-P467L mice with Y27632 abolished the augmentation of myogenic tone (control, 34±5% vs. Y27632, 9±4%, n=7). These findings suggest that PPARγ in vascular muscle normally inhibits rho kinase, influencing responses to NO and myogenic tone in small resistance arteries.

Differential vasoactive effects of sildenafil and tadalafil on cerebral arteries

Phosphodiesterase 5 (PDE5) is associated with migraine pathophysiology, stroke recovery and vasospasm treatment. The potential vascular interplay of PDE5 inhibitors sildenafil, tadalafil and UK-114,542 was studied by intra- versus extra-luminal administration in rat middle cerebral arteries in vitro and on middle meningeal arteries in vivo. By Western blot PDE5 was detected in both cerebral and meningeal arteries, though with minor variations in band intensity between vascular beds. Rat middle cerebral artery diameter was investigated using pressurised arteriography, applying UK-114,542, sildenafil, and tadalafil intra- or extra-luminally. Effects on the dural middle meningeal artery were studied in the in vivo closed cranial window model. At high concentrations, abluminal sildenafil and UK-114,542, but not tadalafil, induced dilatation of the middle cerebral artery. Luminal application elicited a contraction of 4% (sildenafil, P=0.03) and 10% (tadalafil, P=0.02). In vivo, sildenafil, but not tadalafil, dose-dependently dilated middle meningeal artery concomitant to blood pressure reduction (1–3mg/kg);1mg/kg sildenafil inducing 60±14% (P=0.04) and vehicle (DMSO) 13±6% dilatation. In conclusion, PDE5 inhibitors applied luminally had minor contractile effect, whereas abluminal sildenafil induced middle cerebral artery dilatation above therapeutic levels. In vivo, sildenafil dilated middle meningeal artery concomitant with a reduction in blood pressure. Tadalafil had no dilatory effects. PDE5 inhibitors show differential vascular activity in cerebral arteries from healthy animals; arterial dilatation is seen primarily above therapeutic levels. Such findings support clinical studies showing no vasodilator effects of sildenafil on cerebral arteries in healthy subjects.

Dilation by CGRP of middle meningeal artery and reversal by sumatriptan in normal volunteers

Calcitonin gene-related peptide (CGRP) plays a fundamental role in the pathophysiology of neurovascular headaches. CGRP infusion causes headache and dilation of cranial vessels. However, it is unknown to what extent CGRP-induced vasodilation contributes to immediate head pain and whether the migraine-specific abortive drug sumatriptan, a 5-hydroxytryptamine 1B/1D agonist, inhibits CGRP-induced immediate vasodilation and headache. We performed a double-blind, randomized, placebo-controlled, crossover study in 18 healthy volunteers. We recorded circumference changes of the middle meningeal artery (MMA) and middle cerebral artery (MCA) using magnetic resonance angiography before and after infusion (20 minutes) of 1.5 μg/min human αCGRP or placebo (isotonic saline) as well as after a 6-mg sumatriptan subcutaneous injection. Compared with placebo, CGRP caused significant dilation of MMA (p = 0.006) and no dilation of MCA (p = 0.69). Sumatriptan caused a marked contraction of MMA (15%-25.2%) and marginal contraction of MCA (3.9% to 5.3%). Explorative analysis revealed that sumatriptan had a more selective action on MMA compared with MCA on the CGRP day (p < 0.0001) and on the placebo day (p = 0.007). These data suggest that exogenous CGRP dilates extracranial vessels and not intracranial, and that sumatriptan exerts part of its antinociceptive action by constricting MMA and not MCA. This study provides Class I evidence that IV GCRP causes dilation of the MMA but not the MCA in healthy volunteers, and that sumatriptan reverses the dilation of the MMA caused by CGRP.

Angiotensin-(1-7) and low-dose angiotensin II infusion reverse salt-induced endothelial dysfunction via different mechanisms in rat middle cerebral arteries

The goals of this study were to 1) determine the acute effect of ANG-(1-7) on vascular tone in isolated middle cerebral arteries (MCAs) from Sprague-Dawley rats fed a normal salt (NS; 0.4% NaCl) diet, 2) evaluate the ability of chronic intravenous infusion of ANG-(1-7) (4 ng·kg(-1)·min(-1)) for 3 days to restore endothelium-dependent dilation to acetylcholine (ACh) in rats fed a high-salt (HS; 4% NaCl) diet, and 3) determine whether the amelioration of endothelial dysfunction by ANG-(1-7) infusion in rats fed a HS diet is different from the protective effect of low-dose ANG II infusion in salt-fed rats. MCAs from rats fed a NS diet dilated in response to exogenous ANG-(1-7) (10(-10)-10(-5) M). Chronic ANG-(1-7) infusion significantly reduced vascular superoxide levels and restored the nitric oxide-dependent dilation to ACh (10(-10)-10(-5) M) that was lost in MCAs of rats fed a HS diet. Acute vasodilation to ANG-(1-7) and the restoration of ACh-induced dilation by chronic ANG-(1-7) infusion in rats fed a HS diet were blocked by the Mas receptor antagonist [D-ALA(7)]-ANG-(1-7) or the ANG II type 2 receptor antagonist PD-123319 and unaffected by ANG II type 1 receptor blockade with losartan. The restoration of ACh-induced dilation in MCAs of HS-fed rats by chronic intravenous infusion of ANG II (5 ng·kg(-1)·min(-1)) was blocked by losartan and unaffected by d-ALA. These findings demonstrate that circulating ANG-(1-7), working via the Mas receptor, restores endothelium-dependent vasodilation in cerebral resistance arteries of animals fed a HS diet via mechanisms distinct from those activated by low-dose ANG II infusion.

COMPLETE ISOLATED THIRD NERVE PARESIS ASSOSICATED WITH FUSIFORM DILATATION OF MIDDLE CEREBRAL ARTERY

A 28 year-old-male sufferred left third nerve paresis. A pattern of complete and isolated paresis was observed. Neuroimaginings and conventional cerebral angiography revealed abnormally enlarged middle cerebral artery. Because of its fusiform nature, the abnormality was left untreated surgically. The third nerve palsy began to resolve within a week from onset after prednisolone administration. The present case was interesting because of resulting from fusiform dilatation of middle cerebral artery which was the only finding related to the third nevre palsy and early recovering of pupil.

Intracranial hemodynamics during intravenous infusion of glyceryl trinitrate

The mechanisms of glyceryl trinitrate (GTN)-induced headache are not fully elucidated. In this study we administered GTN 0.5 μg/kg/min i.v. for 20 min in six healthy volunteers. Before, during and 60 min after the infusion, we investigated regional cerebral blood flow (rCBF), cerebral blood volume (CBV), both estimated with SPECT, and blood flow velocity (BFV) in the middle cerebral artery (MCA), measured with transcranial Doppler. Headache was scored on a numerical verbal rating (0–10) scale. rCBF was unchanged, CBV was slightly increased (13%) during GTN infusion, whereas BFV decreased both during (20%) and 60 min (15%) after GTN. Headache was short-lived and maximal during infusion. This discrepancy of time-effect curves for the effect of GTN on headache and dilatation of MCA indicates that MCA is most likely not the primary source of pain in GTN-induced headache. The time-effect curves for the effect of GTN on headache and on dilation of MCA differed markedly. This indicates that MCA is most likely not the primary source of pain in GTN-induced headache.

Hypoxia-induced vascular smooth muscle relaxation: increased ATP-sensitive K+ efflux or decreased voltage-sensitive Ca2+ influx?

controversy continues regarding the cellular mechanisms of hypoxic vasodilation. The vascular endothelium may contribute to hypoxic dilations by releasing relaxing factors that act on the smooth muscle ([4][1], [6][2]–[8][3]). In contrast, numerous studies have suggested a role of the vascular

Chronic At1 Receptor Blockade Alters the Mechanisms Mediating Hypoxic Dilation in Middle Cerebral Arteries

The purpose of this study was to determine whether chronic blockade of the angiotensin II (ANG II) AT1 receptor under normal physiological conditions impairs vascular relaxation mechanisms in isolated middle cerebral arteries (MCA). Male Sprague-Dawley rats on a standard diet were given losartan (1 mg/mL) in the drinking water or normal water ad libitum for 7 days. Vessel diameters were measured by television microscopy before and during exposure to various vasodilator agonists and reductions in PO2 from 140 mm Hg to 35-45 mm Hg. Dilations to acetylcholine (1 microM), the stable prostacyclin analogue iloprost (10 pg/mL), and the Gs protein activator cholera toxin (1 ng/mL) were completely eliminated in vessels from losartan-treated animals. However, middle cerebral arteries from control and losartan-treated rats still demonstrated significant dilations in response to reduced PO2. Hypoxic dilation of middle cerebral arteries from control rats was eliminated by indomethacin (1 microM) and unaffected by the NOS inhibitor L-NAME (100 microM) whereas dilation in response to reduced PO2 in middle cerebral arteries from losartan-treated rats was eliminated by L-NAME and unaffected by indomethacin. Middle cerebral arteries from control and losartan-treated animals exhibited similar dilations in response to the NO-donor sodium nitroprusside (1 microM). These data suggest that AT1 receptor activation is important in maintaining normal vascular relaxation mechanisms in cerebral resistance arteries during normal physiological conditions, and that AT1 receptor blockade causes a shift in the mechanisms of hypoxic dilation of middle cerebral arteries from cyclooxygenase metabolites to NO.