Cooperative effect of angiotensin AT1 and endothelin ETA receptor antagonism limits the brain damage after ischemic stroke in rat

The Role of Sartans in the Treatment of Stroke and Subarachnoid Hemorrhage: A Narrative Review of Preclinical and Clinical Studies

Background: Delayed cerebral vasospasm (DCVS) due to aneurysmal subarachnoid hemorrhage (aSAH) and its sequela, delayed cerebral ischemia (DCI), are associated with poor functional outcome. Endothelin-1 (ET-1) is known to play a major role in mediating cerebral vasoconstriction. Angiotensin-II-type-1-receptor antagonists such as Sartans may have a beneficial effect after aSAH by reducing DCVS due to crosstalk with the endothelin system. In this review, we discuss the role of Sartans in the treatment of stroke and their potential impact in aSAH. Methods: We conducted a literature research of the MEDLINE PubMed database in accordance with PRISMA criteria on articles published between 1980 to 2019 reviewing: "Sartans AND ischemic stroke". Of 227 studies, 64 preclinical and 19 clinical trials fulfilled the eligibility criteria. Results: There was a positive effect of Sartans on ischemic stroke in both preclinical and clinical settings (attenuating ischemic brain damage, reducing cerebral inflammation and infarct size, increasing cerebral blood flow). In addition, Sartans reduced DCVS after aSAH in animal models by diminishing the effect of ET-1 mediated vasoconstriction (including cerebral inflammation and cerebral epileptogenic activity reduction, cerebral blood flow autoregulation restoration as well as pressure-dependent cerebral vasoconstriction). Conclusion: Thus, Sartans might play a key role in the treatment of patients with aSAH.

Brain Vasculature and Cognition

There is a complex interaction between the brain and the cerebral vasculature to meet the metabolic demands of the brain for proper function. Preservation of cerebrovascular function and integrity has a central role in this sophisticated communication within the brain, and any derangements can have deleterious acute and chronic consequences. In almost all forms of cognitive impairment, from mild to Alzheimer disease, there are changes in cerebrovascular function and structure leading to decreased cerebral blood flow, which may initiate or worsen cognitive impairment. In this focused review, we discuss the contribution of 2 major vasoactive pathways to cerebrovascular dysfunction and cognitive impairment in an effort to identify early intervention strategies.

CaMKII inhibition with KN93 attenuates endothelin and serotonin receptor-mediated vasoconstriction and prevents subarachnoid hemorrhage-induced deficits in sensorimotor function

Background

It has been suggested that transcriptional upregulation of cerebral artery contractile endothelin (ET_B) and 5-hydroxytryptamine (5-HT_1B) receptors play an important role in the development of late cerebral ischemia and increased vasoconstriction after subarachnoid hemorrhage (SAH). We tested the hypothesis that inhibition of calcium calmodulin-dependent protein kinase II (CaMKII) may reduce cerebral vasoconstriction mediated by endothelin and serotonin receptors and improve neurological outcome after experimental SAH.

Methods

SAH was induced in adult rats by injection of 250 μL autologous blood into the basal cisterns. The CaMKII activity in cerebral vessels was studied by Western blot and immunohistochemistry. The vasomotor responses of middle cerebral and basilar arteries were measured in a sensitive myograph system. The functional outcome was examined by the rotating pole test 2 and 3 days after SAH.

Results

SAH induced a rapid early increase in phosphorylated CaMKII protein at 1 h that was attenuated by cisternal administration of the CaMKII inhibitor KN93 (0.501 μg/kg) 45 min prior and immediately after SAH as evaluated by Western blot. Application of KN93 at 1 h and every 12 h post-SAH significantly reduced vascular CaMKII immunoreactivity at 72 h. In addition, contractile responses of cerebral arteries to endothelin-1 (ET-1) and 5-hydroxycarboxamide (5-CT) were increased at this time-point. KN93 treatment significantly attenuated the contraction induced by ET-1 and 5-CT. Importantly, treatment with the CaMKII inhibitor prevented SAH-induced deficits in neurological function, as evaluated by the rotating pole test, and similar sensorimotor scores were seen in sham-operated animals.

Conclusions

The present study has shown that SAH is associated with increased contractile responses to ET-1 and 5-CT in cerebral arteries and enhanced early activation of CaMKII. Treatment with the CaMKII inhibitor KN93 attenuated the contractile responses and prevented impaired sensorimotor function after SAH.

Smooth muscle cell phenotypic switching in stroke

Disruption of cerebral blood flow after stroke induces cerebral tissue injury through multiple mechanisms that are not yet fully understood. Smooth muscle cells (SMCs) in blood vessel walls play a key role in cerebral blood flow control. Cerebral ischemia triggers these cells to switch to a phenotype that will be either detrimental or beneficial to brain repair. Moreover, SMC can be primarily affected genetically or by toxic metabolic molecules. After stroke, this pathological phenotype has an impact on the incidence, pattern, severity, and outcome of the cerebral ischemic disease. Although little research has been conducted on the pathological role and molecular mechanisms of SMC in cerebrovascular ischemic diseases, some therapeutic targets have already been identified and could be considered for further pharmacological development. We examine these different aspects in this review.

Blockade of endothelin receptors with bosentan limits ischaemia/reperfusion-induced injury in rat ovaries

OBJECTIVE

To investigate the role of endothelin receptors in ovarian ischaemia/reperfusion (I/R) injury in rats using the endothelin receptor antagonist bosentan.

STUDY DESIGN

Group 1: sham operation; Group 2: sham operation and bosentan 60 mg/kg; Group 3: bilateral ovarian ischaemia; Group 4: 3-h period of ischaemia followed by 3h of reperfusion; Groups 5 and 6: bosentan 30 and 60 mg/kg, respectively, with bilateral ovarian ischaemia applied 30 min later; the bilateral ovaries were removed after 3h of ischaemia; Groups 7 and 8: 3h of bilateral ovarian ischaemia was applied, with bosentan 30 and 60 mg/kg, respectively, administered 2.5h after the induction of ischaemia; following the 3-h period of ischaemia, 3h of reperfusion was applied, after which the ovaries were removed.

RESULTS

Ischaemia and I/R decreased superoxide dismutase (SOD) activity and the level of glutathione (GSH) in ovarian tissue, but increased the level of malondialdehyde (MDA) significantly compared with the sham operation group. Bosentan 30 and 60 mg/kg before ischaemia and I/R decreased the MDA level and increased SOD activity and the GSH level in the experimental groups. The serum levels of the inflammatory cytokines interleukin (IL)-1β, IL-6 and tumour necrosis factor-α were also measured in the I/R injury model in rat ovaries. The levels of these cytokines were significantly higher in the ischaemia and I/R groups compared with the sham operation and sham operation plus bosentan groups. The histopathological findings also demonstrated the protective role of bosentan against I/R-induced injury in rat ovaries.

CONCLUSION

Administration of bosentan protects the ovaries against oxidative damage and I/R-induced injury.

A Comparative Study of Neuroprotective Effect of Single and Combined Blockade of AT1 Receptor and PARP-1 in Focal Cerebral Ischaemia in Rat

Background

Cerebral ischaemia results in enhanced expression of type 1 angiotensin receptor and oxidative stress. Free radicals due to oxidative stress lead to excessive DNA damage causing overactivation of poly (ADP-ribose) polymerase-1 resulting in neuronal death. Activation of both type 1 angiotensin receptors and poly (ADP-ribose) polymerase-1 following cerebral ischaemia takes place simultaneously, but until now, no study has explored the effect of combined blockade of both angiotensin type 1 angiotensin receptor and poly (ADP-ribose) polymerase-1 in cerebral ischaemia.

Aim

Our purpose was to compare the effect of single and combined treatment with angiotensin type 1 angiotensin receptor blocker, candesartan, and the poly (ADP-ribose) polymerase-1 inhibitor, 1, 5 isoquinolinediol, on brain damage and oxidative stress in transient focal cerebral ischaemia in rats.

Method

Transient focal cerebral ischaemia was induced in Sprague-Dawley rats by an intraluminal technique for two-hours following 48 h of reperfusion. Candesartan (0·05 mg/kg) was administered just after initiation of ischaemia followed by a repeat administration at 24 h while 1, 5 isoquinolinediol (0·1 mg/kg) was given one-hour after of ischaemia. After 24 h of reperfusion, neurological deficit was evaluated in the different treatment groups. After 48 h of reperfusion, the rats were sacrificed and the brain was isolated. Ischaemic brain damage by 2,3,5 triphenyl tetrazolium chloride staining, oxidative stress markers, and levels of reactive oxygen species were determined biochemically.

Result

Single treatment with candesartan and 1, 5 isoquinolinediol significantly reduced neurological deficit, infarct, and oedema volume as compared to ischaemic control and different vehicle groups for each of the drugs. However, treatment with candesartan + 1, 5 isoquinolinediol offered greater reduction in neurological deficit, cerebral infarct volume, and oedema as compared to single-drug treatments. Furthermore, treatment with candesartan + 1, 5 isoquinolinediol significantly decreased oxidative stress as compared to single treatments with each drug.

Conclusion

The study suggests that blockade of either type 1 angiotensin receptor or poly (ADP-ribose) polymerase-1 alone provides neuroprotection, but the better result was achieved when both type 1 angiotensin receptor and poly (ADP-ribose) polymerase-1 were blocked together by the combined use of their pharmacological inhibitor in transient cerebral ischaemia in rat.

Cytokines and growth factors modify the upregulation of contractile endothelin ET(A) and ET(B) receptors in rat cerebral arteries after organ culture

AIM

Experimental cerebral ischaemia and organ culture of cerebral arteries induce an increased endothelin ET(B) receptor-mediated contraction. The aim of this study was to examine whether cytokines and growth factors, known to be activated in ischaemia, can influence the expression and function of endothelin receptors after organ culture.

METHODS

Rat middle cerebral arteries were cultured for 24 h at 37 °C in humidified 5% CO(2) and air in culture medium alone, or with tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β), platelet-derived growth factor (PDGF), epidermal growth factor (EGF) or basic fibroblast growth factor (bFGF). Concentration-response curves were obtained for sarafotoxin 6c (ET(B) receptor agonist) and endothelin-1 (here ET(A) receptor agonist, because of ET(B) receptor desensitization). The receptor mRNA expression was examined by real-time PCR and the protein expression by immunohistochemistry and Western blot.

RESULTS

Tumour necrosis factor-α (100 ng mL(-1) ) and EGF (20 ng mL(-1) ) potentiated the ET(B) receptor-mediated contraction (increase in pEC(50) without change in E(max) ). bFGF (10 ng mL(-1) ) and IL-1β (10 ng mL(-1) ) induced an enhanced ET(A) receptor-mediated contraction. bFGF (10 ng mL(-1) ) significantly increased the ET(B) mRNA level, and EGF (20 ng mL(-1) ) increased the ET(A) receptor protein. Increased ET(B) receptor mRNA and protein level also were observed after treatment with IL-1β (10 ng mL(-1) ).

CONCLUSION

This study shows that TNF-α, IL-1β, EGF and bFGF can modify the expression and function of endothelin receptors during organ culture. Because there is similar receptor upregulation in experimental stroke, the effect of cytokines and growth factors on endothelin receptor upregulation is an interesting aspect to study in vivo.

Therapeutic effects of postischemic treatment with hypotensive doses of an angiotensin II receptor blocker on transient focal cerebral ischemia

BACKGROUND

Neurovascular protection against cerebral ischemia is not consistently observed with a postischemia hypotensive dose of candesartan. The aim of this study was to determine the levels of brain angiotensin II after reperfusion and the efficacy and therapeutic time window of postischemic treatments with hypotensive doses of candesartan for the treatment of cerebral ischemia.

METHOD

Occlusions of the right middle cerebral artery (60 min) followed by reperfusion were performed using the thread method under halothane anesthesia in Sprague-Dawley (SD) rats. Protein levels of brain angiotensin II and mRNA levels of renin-angiotensin system components were evaluated following reperfusion (n=184 in total). Low-dose or high-dose treatments with candesartan cilexetil (1 or 10 mg/kg per day, respectively) were administered orally immediately following reperfusion once daily for 4 or 7 days (n = 119 in total). An additional group was treated with low-dose candesartan cilexetil after a 12-h delay based on the brain angiotensin II levels (n = 14).

RESULTS

Levels of brain angiotensin II transiently increased 4-12 h after reperfusion, which followed an increase in angiotensinogen mRNA. Candesartan cilexetil treatments significantly reduced blood pressure (BP) in rats administered the high dose and moderately in rats receiving the low dose. A low dose of candesartan cilexetil reduced the infarct size, cerebral edema, and neurological deficits, whereas the high-dose treatments showed limited reductions. Furthermore, oxidative stress following reperfusion was reduced with the low-dose treatments. The therapeutic time window was open for at least 12 h after reperfusion when brain angiotensin II levels had peaked.

CONCLUSION

Postischemic treatments using low hypotensive doses of candesartan cilexetil provided protection against cerebral ischemic injury and may have a clinically relevant therapeutic time window.

Role of angiotensin and endothelin in testicular ischemia reperfusion injury

OBJECTIVES

To determine whether angiotensin and endothelin have any role in testicular ischemia reperfusion injury by investigating the effects of the angiotensin converting enzyme inhibitor enalapril, selective non-peptide angiotensin-II type I blocker losartan and dual endothelin receptor blocker bosentan.

METHODS

Rats were anesthetized with thiopental sodium (50 mg/kg i.p.) before the operation. The left testicular artery and vein of rats were occluded for 1 h; before the bilateral orchiectomy, the organ was allowed to reperfuse for 3 h or 24 h. Enalapril (20 mg/kg i.p.), losartan (30 mg/kg i.p.), bosentan (10 mg/kg i.p.) or vehicle (saline) were given 30 min before reperfusion. Malondialdehyde level was measured in testicular tissue after 3 h of reperfusion. Histological examination was carried out after 24 h of reperfusion.

RESULTS

Ischemia reperfusion caused a significant increase in malondialdehyde level of ipsilateral testis, and histopathological injury in both ipsilateral and contralateral testes. Enalapril, losartan and bosentan treatments prevented the ischemia reperfusion-induced augmentation in malondialdehyde levels. Only bosentan treatment ameloriated ischemia reperfusion-induced histopathological alterations.

CONCLUSIONS

Endothelin might play a more important role in pathogenesis of testicular ischemia reperfusion injury when compared with angiotensin.

Vascular plasticity in cerebrovascular disorders

Cerebral ischemia remains a major cause of morbidity and mortality with little advancement in subacute treatment options. This review aims to cover and discuss novel insight obtained during the last decade into plastic changes in the vasoconstrictor receptor profiles of cerebral arteries and microvessels that takes place after different types of stroke. Receptors like the endothelin type B, angiotensin type 1, and 5-hydroxytryptamine type 1B/1D receptors are upregulated in the smooth muscle layer of cerebral arteries after different types of ischemic stroke as well as after subarachnoid hemorrhage, yielding rather dramatic changes in the contractility of the vessels. Some of the signal transduction processes mediating this receptor upregulation have been elucidated. In particular the extracellular regulated kinase 1/2 pathway, which is activated early in the process, has proven to be a promising therapeutic target for prevention of vasoconstrictor receptor upregulation after stroke. Together, those findings provide new perspectives on the pathophysiology of ischemic stroke and point toward a novel way of reducing vasoconstriction, neuronal cell death, and thus neurologic deficits after stroke.

Cerebral ischemia induces microvascular pro-inflammatory cytokine expression via the MEK/ERK pathway

BACKGROUND

Cerebral ischemia from middle cerebral artery wall (MCA) occlusion results in increased expression of cerebrovascular endothelin and angiotensin receptors and activation of the mitogen-activated protein kinase (MAPK) pathway, as well as reduced local cerebral blood flow and increased levels of pro-inflammatory mediators in the infarct region. In this study, we hypothesised that inhibition of the cerebrovascular inflammatory reaction with a specific MEK1/2 inhibitor (U0126) to block transcription or a combined receptor blockade would reduce infarct size and improve neurological score.

METHODS

Rats were subjected to a 2-hours middle cerebral artery occlusion (MCAO) followed by reperfusion for 48 hours. Two groups of treated animals were studied; (i) one group received intraperitoneal administration of a specific MEK1/2 inhibitor (U0126) starting at 0, 6, or 12 hours after the occlusion, and (ii) a second group received two specific receptor antagonists (a combination of the angiotensin AT1 receptor inhibitor Candesartan and the endothelin ETA receptor antagonist ZD1611), given immediately after occlusion. The middle cerebral arteries, microvessels and brain tissue were harvested; and the expressions of tumor necrosis factor-alpha (TNF-alpha), interleukin-1ss (IL-1ss), interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS) and phosphorylated ERK1/2, p38 and JNK were analysed using immunohistochemistry.

RESULTS

We observed an infarct volume of 25 +/- 2% of total brain volume, and reduced neurological function 2 days after MCAO followed by 48 hours of recirculation. Immunohistochemistry revealed enhanced expression of TNF-alpha, IL-1ss, IL-6 and iNOS, as well as elevated levels of phosphorylated ERK1/2 in smooth muscle cells of ischemic MCA and in associated intracerebral microvessels. U0126, given intraperitoneal at zero or 6 hours after the ischemic event, but not at 12 hours, reduced the infarct volume (11.7 +/- 2% and 15 +/- 3%, respectively), normalized pERK1/2, and prevented elevation of the expressions of TNF-alpha IL-1ss, IL-6 and iNOS. Combined inhibition of angiotensin AT1 and endothelin ETA receptors decreased the volume of brain damaged (12.3 +/- 3; P < 0.05) but only slightly reduced MCAO-induced enhanced expression of iNOS and cytokines

CONCLUSION

The present study shows elevated microvascular expression of TNF-alpha, IL-1ss, IL-6 and iNOS following focal ischemia, and shows that this expression is transcriptionally regulated via the MEK/ERK pathway.

Protective effect of quercetin against intracerebral streptozotocin induced reduction in cerebral blood flow and impairment of memory in mice

The aim of the present study is to investigate the effect of quercetin, a naturally occurring flavonoid, on cerebral blood flow (CBF), brain energy metabolism, memory impairment, oxidative stress and cholinergic dysfunction in brain following intracerebral (i.c.) streptozotocin (STZ) administration in mice. STZ (0.5mg/kg, i.c.) was administered twice at an interval of 48h. We found a significant reduction in CBF as measured by Laser Doppler Flowmetry (LDF). The brain energy metabolism was also altered as evidenced by significant reduction in brain ATP content. Daily treatment with quercetin (2.5, 5 and 10mg/kg, p.o.) starting from the first dose of STZ showed a dose-dependent restoration of CBF and ATP content. Further, quercetin prevented STZ induced memory impairment as assessed by Morris water maze and passive avoidance tests. Biochemical analysis revealed that STZ significantly increased malondialdehyde (MDA), nitrite and depleted glutathione (GSH) levels in the mice brain. Quercetin decreased oxidative and nitrosative stress as evidenced by a significant decrease in MDA, nitrite and increase in GSH levels. Quercetin also attenuated elevated acetylcholinesterase activity in the STZ-treated mice. Neither STZ (i.c.) nor quercetin showed any change in locomotor activity and blood glucose level. The present study demonstrates the beneficial effects of quercetin in improving CBF along with preventing memory impairment, oxidative stress, altered brain energy metabolism and cholinergic dysfunction caused by STZ in mice. Therefore, consumption of dietary stuff rich in quercetin should be encouraged to ward off dementia associated with vascular and neurodegenerative disorders.

Role of angiotensin II in the response to endothelin-1 of goat cerebral arteries after ischemia-reperfusion

As angiotensin II may underlie the deleterious effects of some vascular diseases, we have examined the role of this peptide on the cerbrovascular endothelin-1 action after ischemia-reperfusion. In anesthetized goats, 1 hour-occlusion followed by 1 hour-reperfusion of the left middle cerebral artery (MCA) was induced, and then segments 3-mm in length from branches of the right MCA (control) and the left MCA (ischemic) were obtained for isometric tension recording. Endothelin-1 (10(-11)-10(-7) M) produced a contraction that was higher in ischemic than in control arteries, and in control but not in ischemic arteries this contraction was potentiated by angiotensin II (10(-7) M). Losartan (3 x 10(-6) M), antagonist of AT1 receptors, did not affect the response to endothelin-1 in control arteries, but reduced it both in ischemic arteries and angiotensin II-treated control arteries. PD123,319 (3 x 10(-6) M), antagonist of AT2 receptors, or the inhibitor of nitric oxide synthesis L-NAME (10(-4) M) did not alter the arterial effects of endothelin-1. Therefore, angiotensin II may potentiate the constriction to endothelin-1 in normal cerebral arteries by activating AT1 receptors. The observed cerebrovascular increased response to endothelin-1 after ischemia-reperfusion might be related in part to activation of AT1 receptors under this condition.

Hibernation-like state induced by an opioid peptide protects against experimental stroke

BACKGROUND

Delta opioid peptide [D-ala2,D-leU5]enkephalin (DADLE) induces hibernation in summer ground squirrels, and enhances preservation and survival of isolated or transplanted lungs and hearts. In the present study, we investigated the protective effect of DADLE in the central nervous system.

RESULTS

Adult Sprague-Dawley rats were pretreated with DADLE (4 mg/kg every 2 h x 4 injections, i.p.) or saline prior to unilateral occlusion of the middle cerebral artery (MCA). Daily behavioral tests revealed that ischemic animals treated with DADLE did not show any significant behavioral dysfunctions compared with saline-treated ischemic animals. Opioid antagonists only transiently inhibited the protective effect of DADLE, indicating the participation of non-opioid mechanisms in DADLE neuroprotection. Histological examination using triphenyltetrazolium chloride (TTC) revealed that brains from ischemic animals treated with DADLE, either alone or with adjuvant opioid blockers, exhibited almost completely intact striata. In contrast, brains from ischemic animals that received saline showed significant infarction in the lateral striatum. Analyses of apoptotic cell death revealed a significant increase in the p-53 mRNA expression in the striatum of ischemic animals that received saline, while those that received DADLE exhibited near normal striatal p-53 expression. This protective effect was accompanied by significant increments in protein levels of glial cell line-derived neurotrophic factor in the striatum of DADLE-treated ischemic animals.

CONCLUSION

These results indicate that DADLE protected against necrotic and apoptotic cell death processes associated with ischemia-reperfusion injury. The present study demonstrates that delta opioids are crucially involved in stroke, suggesting that the opioid system is important in the study of brain injury and protection.

Enhanced cerebrovascular expression of matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 via the MEK/ERK pathway during cerebral ischemia in the rat

Background

Cerebral ischemia is usually characterized by a reduction in local blood flow and metabolism and by disruption of the blood-brain barrier in the infarct region. The formation of oedema and opening of the blood-brain barrier in stroke is associated with enhanced expression of metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1).

Results

Here, we found an infarct volume of 24.8 ± 2% and a reduced neurological function after two hours of middle cerebral artery occlusion (MCAO), followed by 48 hours of recirculation in rat. Immunocytochemistry and confocal microscopy revealed enhanced expression of MMP-9, TIMP-1, and phosphorylated ERK1/2 in the smooth muscle cells of the ischemic MCA and associated intracerebral microvessels. The specific MEK1/2 inhibitor U0126, given intraperitoneal zero or 6 hours after the ischemic event, reduced the infarct volume significantly (11.8 ± 2% and 14.6 ± 3%, respectively; P < 0.05), improved neurological function, normalized expression of phosphorylated ERK1/2, and reduced expression of MMP-9 and TIMP-1 in the vessel walls. Administration of U0126 12 hours after MCAO did not alter the expression of MMP-9. Immunocytochemistry showed no overlap in expression between MMP-9/TIMP-1 and the astrocyte/glial cell marker GFAP in the vessel walls.

Conclusion

These data are the first to show that the elevated vascular expression of MMP-9 and TIMP-1, associated with breakdown of the blood-brain barrier following focal ischemia, are transcriptionally regulated via the MEK/ERK pathway.

Enhanced expressions of microvascular smooth muscle receptors after focal cerebral ischemia occur via the MAPK MEK/ERK pathway

BACKGROUND

MEK1/2 is a serine/threonine protein that phosphorylates extracellular signal-regulated kinase (ERK1/2). Cerebral ischemia results in enhanced expression of cerebrovascular contractile receptors in the middle cerebral artery (MCA) leading to the ischemic region. Here we explored the role of the MEK/ERK pathway in receptor expression following ischemic brain injury using the specific MEK1 inhibitor U0126.

METHODS AND RESULT

Rats were subjected to a 2-h middle cerebral artery occlusion (MCAO) followed by reperfusion for 48-h and the ischemic area was calculated. The expression of phosphorylated ERK1/2 and Elk-1, and of endothelin ETA and ETB, angiotensin AT1, and 5-hydroxytryptamine 5-HT1B receptors were analyzed with immunohistochemistry using confocal microscopy in cerebral arteries, microvessels and in brain tissue. The expression of endothelin ETB receptor was analyzed by quantitative Western blot. We demonstrate that there is an increase in the number of contractile smooth muscle receptors in the MCA and in micro- vessels within the ischemic region. The enhanced expression occurs in the smooth muscle cells as verified by co-localization studies. This receptor upregulation is furthermore associated with enhanced expression of pERK1/2 and of transcription factor pElk-1 in the vascular smooth muscle cells. Blockade of transcription with the MEK1 inhibitor U0126, given at the onset of reperfusion or as late as 6 hours after the insult, reduced transcription (pERK1/2 and pElk-1), the enhanced vascular receptor expression, and attenuated the cerebral infarct and improved neurology score.

CONCLUSION

Our results show that MCAO results in upregulation of cerebrovascular ETB, AT1 and 5-HT1B receptors. Blockade of this event with a MEK1 inhibitor as late as 6 h after the insult reduced the enhanced vascular receptor expression and the associated cerebral infarction.