Expression of ET(A) and ET(B) receptor mRNA in human cerebral arteries

Protein kinase C-inhibition reduces critical weight loss and improves functional outcome after experimental subarachnoid haemorrhage

OBJECTIVES

Subarachnoid haemorrhage (SAH) carries a high burden of morbidity and mortality. One in three patients develop vasospasm, which is associated with Delayed Cerebral Ischemia. The pathophysiology includes vasoconstrictor receptor upregulation in cerebral arteries. The protein kinase C - inhibitor RO-31-7549 reduces the expression of several vasoconstrictor receptors and normalizes cerebral blood flow in experimental SAH but functional and behavioural effects are unknown. This study was undertaken to analyse functional outcomes up to 14 days after experimental SAH.

MATERIALS AND METHODS

54 male rats were randomised to experimental SAH or sham, using the pre-chiasmatic, single injection model, and subsequent treatment or vehicle. 42 remained for final analysis. The animals were euthanized on day 14 or when reaching a humane endpoint. The primary endpoint was overall survival, defined as either spontaneous mortality or when reaching a predefined humane endpoint. The secondary outcomes were differences in the rotating pole test, weight, open field test, novel object recognition and qPCR of selected inflammatory markers.

RESULTS

In the vehicle group 6/15 rats reached the humane endpoint of >20 % weight loss compared to 1/14 in the treatment group. This resulted in a significant reduced risk of early euthanasia due to >20 % weight loss of HR 0.15 (0.03-0.66, p = 0.04). Furthermore, the treatment group did significantly better on the rotating pole test, RR 0.64 (0.47-0.91, p = 0.02).

CONCLUSION

RO-31-7549 improved outcomes in terms >20 % weight loss and rotating pole performance after experimental SAH and could be investigated.

Reduced Mechanical Stretch Induces Enhanced Endothelin B Receptor-Mediated Contractility via Activation of Focal Adhesion Kinase and Extracellular Regulated Kinase 1/2 in Cerebral Arteries from Rat

Cerebral ischaemia results in enhanced endothelin B (ETB ) receptor-mediated contraction and receptor protein expression in the affected cerebrovascular smooth muscle cells (SMC). Organ culture of cerebral arteries is a method to induce similar alterations in ETB receptor expression. We suggest that rapid and sustained reduction in wall tension/stretch is a possible trigger mechanism for this vascular remodelling. Isolated rat middle cerebral artery (MCA) segments were incubated in a wire myograph with or without mechanical stretch, prior to assessment of their contractile response to the selective ETB receptor agonist sarafotoxin 6c. The involvement of extracellular regulated kinase (ERK) 1/2 and focal adhesion kinase (FAK) was studied by their specific inhibitors U0126 and PF-228, respectively. Compared with their stretched counterparts, unstretched MCA segments showed a significantly increased ETB receptor-mediated contractile response after 12 hr of incubation, which was attenuated by either U0126 or PF-228. The functionally increased ETB -mediated contractility could be attributed to two different mechanisms: (i) a difference in ETB receptor localization from primarily endothelial expression to SMC expression and (ii) an increased calcium sensitivity of the SMCs due to an increased expression of the calcium channel transient receptor potential canonical 1. Collectively, our results present a possible mechanism linking lack of vessel wall stretch/tension to changes in ETB receptor-mediated contractility via triggering of an early mechanosensitive signalling pathway involving ERK1/2 and FAK signalling. A mechanism likely to be an initiating factor for the increased ETB receptor-mediated contractility found after cerebral ischaemia.

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.

Permanent distal occlusion of middle cerebral artery in rat causes local increased ETB, 5-HT₁B and AT₁ receptor-mediated contractility downstream of occlusion

BACKGROUND/AIMS

In response to experimental stroke, a characteristic functional and expressional upregulation of contractile G-protein-coupled receptors has been uncovered in the affected cerebral vasculature; however, the mechanism initiating this phenomenon remains unknown.

METHODS

Using a model of permanent distal occlusion of rat middle cerebral arteries, we investigated whether there was a regional difference in receptor-mediated contractility of segments located upstream and downstream of the occlusion site. The contractile response to endothelin, angiotensin and 5-hydroxytryptamine receptor stimulation was studied by sensitive wire myograph.

RESULTS

Only downstream segments exhibited an augmented contractile response to stimulation with each of the three ligands, with the response towards sarafotoxin 6c being especially augmented compared to sham, upstream and contralateral controls. This functional increase did not seem to relate to ischemic tissue damage, inflammatory cell infiltration or the element of reperfusion. Interestingly, immunohistochemistry did not show any difference in the level of immunoreactivity towards endothelin B (ETB) receptors between groups.

CONCLUSION

Single artery occlusion without significant visible infarct resulted in locally increased ETB, angiotensin type 1 and 5-hydroxytryptamine 1B receptor-mediated contractile responses only in segments located downstream of the occlusion site. This suggests lack of wall stress as an initiating trigger leading to regulation of contractile response after cerebral stroke.

Efficacy of the specific endothelin a receptor antagonist zibotentan (ZD4054) in colorectal cancer: a preclinical study

Endothelin 1 (ET-1) is overexpressed in cancer, contributing to disease progression. We previously showed that ET-1 stimulated proliferative, migratory, and contractile tumorigenic effects via the ET(A) receptor. Here, for the first time, we evaluate zibotentan, a specific ET(A) receptor antagonist, in the setting of colorectal cancer, in cellular models. Pharmacologic characteristics were further determined in patient tissues. Colorectal cancer lines (n = 4) and fibroblast strains (n = 6), isolated from uninvolved areas of colorectal cancer specimens, were exposed to ET-1 and/or ET(A)/(B) receptor antagonists. Proliferation (methylene blue), migration (scratch wounds), and contraction (gel lattices) were assessed. Receptor distribution and binding characteristics (K(d), B(max)) were determined using autoradiography on tissue sections and homogenates and cytospun cells, supported by immunohistochemistry. Proliferation was inhibited by ET(A) (zibotentan > BQ123; P < 0.05), migration by ET(B) > ET(A), and contraction by combined ET(A) and ET(B) antagonism. Intense ET-1 stromal binding correlated with fibroblasts and endothelial cells. Colorectal cancer lines and fibroblasts revealed high density and affinity ET-1 binding (B(max) = 2.435 fmol/1 × 10(6) cells, K(d) = 367.7 pmol/L; B(max) = 3.03 fmol/1 × 10(6) cells, K(d) = 213.6 pmol/L). In cancer tissues, ET(A) receptor antagonists (zibotentan; BQ123) reduced ET-1 binding more effectively (IC(50): 0.1-10 μmol/L) than ET(B) receptor antagonist BQ788 (∼IC(50), 1 mmol/L). ET-1 stimulated cancer-contributory processes. Its localization to tumor stroma, with greatest binding/affinity to fibroblasts, implicates these cells in tumor progression. ET(A) receptor upregulation in cancer tissues and its role in tumorigenic processes show the receptor's importance in therapeutic targeting. Zibotentan, the most specific ET(A) receptor antagonist available, showed the greatest inhibition of ET-1 binding. With its known safety profile, we provide evidence for zibotentan's potential role as adjuvant therapy in colorectal cancer.

Secondhand smoke exposure induces Raf/ERK/MAPK-mediated upregulation of cerebrovascular endothelin ETA receptors

BACKGROUND

Cigarette smoking enhances the risk of stroke. However, the underlying molecular mechanisms are largely unknown. The present study established an in vivo rat secondhand cigarette smoking (SHS) model and examined the hypothesis that SHS upregulates endothelin receptors with increased cerebrovascular contraction via the Raf/extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinases (MAPK) pathway.

RESULTS

Rats were exposed to SHS for up to 8 weeks. The cerebral artery vasoconstriction was recorded by a sensitive myograph. The mRNA and protein expressions for endothelin receptors in cerebral arteries were studied by real-time PCR and Western blot. Compared to fresh air exposed rats, cerebral arteries from SHS rats exhibited stronger contractile responses (P < 0.05) mediated by endothelin type A (ETA) receptors. The expressions of mRNA and protein for ETA receptors in the cerebral arteries from SHS rats were higher (P < 0.05) than that in control. SHS did not affect endothelin type B (ETB) receptor-mediated contractions, mRNA or protein levels. The results suggest that SHS upregulates ETA, but not ETB receptors in vivo. After SHS exposure, the mRNA levels of Raf-1 and ERK1/2, the protein expression of phosphorylated (p)-Raf-1 and p-ERK1/2 were increased (P < 0.05). Raf-1 inhibitor, GW5074 suppressed the enhanced ETA receptor-mediated contraction, mRNA and protein levels induced by SHS. In addition, GW5074 inhibited the SHS-caused increased mRNA and phosphorylated protein levels of Raf-1 and ERK1/2, suggesting that SHS induces activation of the Raf/ERK/MAPK pathway.

CONCLUSIONS

SHS upregulates cerebrovascular ETA receptors via the Raf/ERK/MAPK pathway, which provides novel understanding of mechanisms involved in SHS-associated stroke.

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.

Endothelin-1 as a neuropeptide: neurotransmitter or neurovascular effects?

Endothelin-1 (ET-1) is an endothelium-derived peptide that also possesses potent mitogenic activity. There is also a suggestion the ET-1 is a neuropeptide, based mainly on its histological identification in both the central and peripheral nervous system in a number of species, including man. A neuropeptide role for ET-1 is supported by studies showing a variety of effects caused following its administration into different regions of the brain and by application to peripheral nerves. In addition there are studies proposing that ET-1 is implicated in a number of neural circuits where its transmitter affects range from a role in pain and temperature control to its action on the hypothalamo-neurosecretory system. While the effect of ET-1 on nerve tissue is beyond doubt, its action on nerve blood flow is often ignored. Here, we review data generated in a number of species and using a variety of experimental models. Studies range from those showing the distribution of ET-1 and its receptors in nerve tissue to those describing numerous neurally-mediated effects of ET-1.

Transcriptional activation of endothelial cells by TGFβ coincides with acute microvascular plasticity following focal spinal cord ischaemia/reperfusion injury

Microvascular dysfunction, loss of vascular support, ischaemia and sub-acute vascular instability in surviving blood vessels contribute to secondary injury following SCI (spinal cord injury). Neither the precise temporal profile of the cellular dynamics of spinal microvasculature nor the potential molecular effectors regulating this plasticity are well understood. TGFβ (transforming growth factor β) isoforms have been shown to be rapidly increased in response to SCI and CNS (central nervous system) ischaemia, but no data exist regarding their contribution to microvascular dysfunction following SCI. To examine these issues, in the present study we used a model of focal spinal cord ischaemia/reperfusion SCI to examine the cellular response(s) of affected microvessels from 30 min to 14 days post-ischaemia. Spinal endothelial cells were isolated from affected tissue and subjected to focused microarray analysis of TGFβ-responsive/related mRNAs 6 and 24 h post-SCI. Immunohistochemical analyses of histopathology show neuronal disruption/loss and astroglial regression from spinal microvessels by 3 h post-ischaemia, with complete dissolution of functional endfeet (loss of aquaporin-4) by 12 h post-ischaemia. Coincident with this microvascular plasticity, results from microarray analyses show 9 out of 22 TGFβ-responsive mRNAs significantly up-regulated by 6 h post-ischaemia. Of these, serpine 1/PAI-1 (plasminogen-activator inhibitor 1) demonstrated the greatest increase (>40-fold). Furthermore, uPA (urokinase-type plasminogen activator), another member of the PAS (plasminogen activator system), was also significantly increased (>7.5-fold). These results, along with other select up-regulated mRNAs, were confirmed biochemically or immunohistochemically. Taken together, these results implicate TGFβ as a potential molecular effector of the anatomical and functional plasticity of microvessels following SCI.

Heat stress alters G-protein coupled receptor-mediated function and endothelium-dependent relaxation in rat mesenteric artery

Heat stress has been demonstrated to have strong cardiovascular effects. However, the underlying mechanism-mediated cardiovascular effects are still not fully understood. The present study was designed to examine if heat stress alters vascular G-protein coupled receptor-mediated vasomotion and endothelium function in rat mesenteric artery. Rats were divided into two groups, heat stress rats and control. The G-protein coupled receptors of endothelin type B (ETB) receptor-, endothelin type A (ETA) receptor-, 5-hydroxytryptamine (5-HT) receptor-, calcitonin gene-related peptide (CGRP) receptor-, alpha-adrenoceptor-mediated vosoactivity and endothelium-dependent relaxation on rat mesenteric artery ring segments were monitored by a myograph system. The plasma level of CGRP was determined by radioimmunological assay. Compared with control arterial segments, the contractile response curves of sarafotoxin 6c, a selective ETB receptor agonist and 5-HT in the arterial segments from heat stress rats were shifted towards left. An increased maximum contraction (Emax) induced by sarafotoxin 6c, but not 5-HT, was seen in the arterial segments from heat stress rats. CGRP-induced relaxation in endothelium-denuded arterial segments from heat stress rats was enhanced. The relaxation in endothelium-intact arterial segments induced by acetylcholine was significantly decreased in heat stress rats. In addition, the plasma concentration of CGRP was increased in heat stress rats. The endothelium-dependent relaxation was characterized and shown there was a decrease in nitric oxide and endothelium-derived hyperpolarizing factor-mediated relaxation in the arterial segments from heat stress rats. In conclusion, heat stress induces an enhanced vascular endothelin ETB-, 5-HT-receptors-mediated contraction, an enhanced CGRP-receptor-induced relaxation and damage to endothelium-dependent relaxation.

High-dose bosentan in the prevention and treatment of subarachnoid hemorrhage-induced cerebral vasospasm: an open-label feasibility study

OBJECTIVE

To evaluate the safety of high-dosages of the endothelin ET(A/B )receptor antagonist bosentan in SAH patients at high-vasospasm risk.

METHODS

Ten Fisher group-3 SAH patients, enrolled within 96 h of ictus, received bosentan in a dose-escalation manner (20, 30, 40 mg/kg/day orally every 4 hours on treatment days 1, 2, and 3 respectively, to a maximum dose of 4000 mg/day), followed by maintenance of the maximum tolerated dose until 14 days post-SAH or vasospasm resolution. Further management followed standard protocols: nimodipine in all patients; daily transcranial Doppler (TCD); "triple-H"/endovascular treatment, as indicated.

RESULTS

Two of the ten patients never developed any clinical or TCD signs of vasospasm; the other eight patients exhibited some elevation of TCD velocities during the vasospasm watch period. Four of the eight patients remained asymptomatic; of them, one had only mild elevation on peak systolic velocities, thought to represent hyperemia. The other three were further assessed with CT-angiography; this revealed moderate vasospasm (asymptomatic) in only one patient. The remaining four patients developed symptomatic vasospasm requiring endovascular treatment; two developed cerebral infarction; both had started bosentan relatively later than the other subjects. The most common adverse drug effects were flushing and transient liver enzyme elevations, reversible in all. Two patients had ALT/AST elevations >3x normal limit, requiring bosentan-dose reduction or discontinuation (one case each).

CONCLUSION

High-dose bosentan (up to 40 mg/kg/day) appears to be safe in SAH patients at high risk of developing vasospasm. Further studies are required to properly investigate the efficacy of this regimen in the prevention and treatment of SAH-induced vasospasm.

Altered endothelin receptor subtypes in colorectal cancer

BACKGROUND

The vasoactive peptide endothelin-1 (ET-1) acts via two endothelin receptor subtypes, ETA (ETAR) and ETB (ETBR). ET-1 and ETAR are overexpressed in colorectal cancer tissues. In vitro, ET-1 acting via ETAR, is a mitogen for colorectal cancer cells. To identify other potential stimulatory loops, we investigated the distribution and cell-specific localization of both ETAR and ETBR in tissue sections from patients with colorectal cancer.

METHODS

Frozen sections from specimens of colorectal cancer (n=9) and normal colon (n=9) were cut and subjected to either (i) autoradiography or (ii) a combination of cell type-specific immunohistochemistry, using antibodies against fibroblasts (AS02), endothelial cells (CD31) or nerve fibres (NF200) and in-vitro receptor microautoradiography, using ETAR-specific and ETBR-specific radioligands.

RESULTS

ETARs were upregulated in all cell types, apart from nerve, in cancer compared with normal colon (1:1.59 normal to cancer). Specifically, ETAR binding was highest in cancer-associated blood vessels and fibroblasts and to a lesser extent in epithelial cancer cells. In contrast, ETBRs were the predominant receptors in normal colon (1:0.59 normal to cancer) and were markedly down-regulated in cancer-associated blood vessels, fibroblasts and to a lesser extent in epithelial cells. Nerve colocalization was demonstrated, but remained unchanged for all tissues.

CONCLUSION

The shift in ET receptor binding observed in epithelial cancer cells and cancer-associated fibroblasts and endothelial cells may favour ET-1 signals contributing to colorectal cancer growth and neovascularization via ETAR. This may provide the basis for therapeutic use of specific ETAR antagonists as adjuvant treatment of colorectal cancer.

Gene expression profiling in the human middle cerebral artery after cerebral ischemia

We have investigated the gene expression in human middle cerebral artery (MCA) after ischemia. Ischemic stroke affects the perfusion in the affected area and experimental cerebral ischemia results in upregulation of vasopressor receptors in the MCA leading to the ischemic area. We obtained human MCA samples distributing to the ischemic area, 7-10 days post-stroke. The gene expression was examined with real-time polymerase chain reaction (PCR) and microarray, proteins were studied with immunohistochemistry. We investigated genes previously shown to be upregulated in animal models of cerebral ischemia (e.g. ET(A), ET(B), AT1, AT2, and 5-HT(2A/1B/1D)). Their mRNA expression was increased compared with controls, consistent with findings in experimental stroke. Immunohistochemistry showed upregulation of the receptors localized on the smooth muscle cells. The gene expression was profiled with microarray and seven genes chosen for further investigation with real-time PCR; ELK3, LY64, Metallothionin IG, POU3F4, Actin alpha2, RhoA and smoothelin. Six of these were regulated the same way when confirming array expression with real-time PCR. Gene expression studies in the human MCA leading to the ischemic region is similar to that seen after MCA occlusion in rats. We found new genes that support the dynamic changes that occur in the MCA distributing to the ischemic region.

Enhanced G-protein coupled receptors-mediated contraction and reduced endothelium-dependent relaxation in hypertension

The present study was designed to demonstrate a hypothesis that some G-protein coupled receptors are up-regulated and a dysfunction of endothelium occurs in hypertension. The arteries from hypertensive patients and spontaneously hypertensive rats (SHR) were tested. An in vitro myograph system was used to obtain concentration-contraction curves mediated by endothelin ET(A), endothelin ET(B), 5-hydroxytryptamine 2A (5-HT2A)-receptors and alpha1-adrenoceptors in the arterial segments. In hypertensive patients, the maximum contractions (Emax) induced by endothelin ET(B), endothelin ET(A) and 5-HT receptors were significantly increased with elevated pEC50 values, while a significantly leftward shift of alpha1-adrenoceptor-mediated contraction was seen. Similar results were obtained in SHR. Specific antagonists for 5-HT2A receptors or alpha1-adrenoceptors rightward shifted the concentration-contractile curves induced by 5-HT or noradrenaline, while the Emax were not significantly altered, suggesting that the contractions were mediated by 5-HT2A receptors and alpha1-adrenoceptors, respectively. Endothelium-dependent maximum relaxation (Rmax) in the arterial segments induced by acetylcholine was significantly decreased in both hypertensive patients and SHR. In addition, nitric oxide- and endothelium-derived hyperpolarizing factor-mediated dilatations were decreased significantly and the arterial endothelial cells were in part lost in SHR. In conclusion, endothelin ET(B), endothelin ET(A), 5-HT2A receptor- and alpha-adrenoceptor-mediated contractions were increased in hypertension, while the endothelium and its functions were damaged.

Involvement of protein kinases on the upregulation of endothelin receptors in rat basilar and mesenteric arteries

Endothelin(B) (ET(B)) receptors are upregulated in experimental stroke or after 24 hrs of organ culture. This upregulation is manifested both as stronger contraction and as an increase in ET(B) receptor messenger RNA (mRNA) levels. The present study was designed to evaluate the importance of protein kinases (c-Jun N-terminal kinase [JNK], protein kinase C [PKC], and extracellular signal-regulated kinase [ERK1/2]) in ET(B) receptor upregulation after organ culture. Rat basilar and mesenteric arteries were incubated for 24 hrs in Dulbecco's modified Eagle's medium (DMEM) with or without the PKC inhibitor, RO-31-7549; the ERK1/2 inhibitor, SB386023; or the JNK inhibitor, SP600125, added 3, 6, or 12 hrs after initiation of incubation. Subsequently, vessel segments were mounted in myographs and the contractile responses to ET-1 and sarafotoxin 6c were studied. The ET(B) and ET(A) receptor mRNA levels were determined with a real-time polymerase chain reaction (PCR). The cellular localization and protein level of ET(B) receptors were evaluated by immunohistochemistry. The PKC and ERK1/2 inhibitors attenuated the contraction induced by S6c in the basilar arteries more than in the mesenteric arteries. The efficiency of the inhibitors was proportional to the incubation time. Real-time PCR showed a decrease in the ET(B) receptor mRNA levels in arteries treated with PKC or ERK inhibitors. The JNK inhibitor had a significant inhibitory effect on ET(B) receptor upregulation in the basilar arteries. Immunohistochemistry revealed that the ET(B) receptor upregulation occured in the smooth-muscle cells and that it had the same pattern as in the quantitative PCR. Our results show that the PKC, ERK1/2, and JNK are more important for the upregulation of contractile ET(B) receptors in cerebral arteries compared with mesenteric arteries. ERK1/2 seems to be more important for the ET(B) receptor upregulation, as compared with PKC and JNK. The evaluation of the time dependency suggests that the phenomenon can be reversed even after its initiation.

Up-Regulation of alpha1A-Adrenoceptors in Rat Mesenteric Artery Involves Intracellular Signal Pathways

The aim of the present study was to investigate if there is an altered expression of alpha-adrenoceptors during organ culture of rat mesenteric artery segments by using a sensitive pharmacological method and molecular biological techniques. Noradrenalin (NA) induced contraction via alpha1-adrenoceptors. The contraction and alpha1A-adrenoceptor mRNA levels were elevated during organ culture. Transcriptional inhibitor actinomycin D, translational inhibitor cycloheximide, protein kinase C inhibitors (staurosporine and RO31-8220) and mitogen-activated protein kinase (MAPK) pathway inhibitors (SB386023, U0126 and SB239063) prevented the increase in NA-induced contractions. The amount of alpha1A-adrenoceptor mRNA was significantly lower in the artery segments cultured for 1 day in the presence of specific MAPK extracellular signal-regulated protein kinase1/2 pathway inhibitor SB386023 than that of the cultured controls. SB386023 did not affect alpha2-adrenoceptor mRNA level. Our results suggest that the up-regulation of alpha1A-adrenoceptors involves transcription and intracellular signal transduction via the protein kinase C and the ERK 1/2 pathways.

Vasodilator Effect of Endothelin in Cutaneous Microcirculation of Heart Failure Patients

The heart failure syndrome is associated with a reduced vasodilatory capacity in cutaneous microvessels. The aim of this study was to investigate the hypothesis that an altered activity of the endothelin system contributes to this reduction. The skin blood flow was recorded by laser Doppler flowmetry in patients with congestive heart failure and in age- and gender-matched controls without clinical signs of heart failure. The vessels were stimulated by iontophoretic administration of endothelin-1. The involvement of the endothelin(A) receptor was studied by co-administration of a specific antagonist; the role of the endothelin(B) receptor was studied by the administration of the selective agonist sarafotoxin 6c. The plasma levels of endothelin-1, C-reactive peptide and N-terminal-pro-Brain Natriuretic Peptide were elevated in heart failure patients. Unexpected, endothelin-1 induced an endothelin(A) mediated vasodilation. In the heart failure group the dilation was reduced to less than half as compared to control. The response to local warming was reduced in parallel indicating that the attenuation of the response in the heart failure group can be explained by the general decline in vascular reactivity. The response to endothelin(B) receptor stimulation did not differ between the groups. The reduction in endothelin-1 responsiveness is paralleled by a general reduction in microvascular vasodilatory capacity, a phenomenon of increased vascular stiffness in the of heart failure subjects.

Endothelin-1 and endothelin receptors in the basilar artery of the capybara

Little is known about cerebral vasculature of capybara, which seems may serve as a natural model of studying changes in cerebral circulation due to internal carotid artery atrophy at animal sexual maturation. This is the first study of the light- and electron-immunocytochemical localisation of endothelin-1 (ET-1) and ETA and ETB endothelin receptors in the basilar artery of capybaras (6 to 12-month-old females and males) using an ExtrAvidin detection method. All animals examined showed similar patterns of immunoreactivity. Immunoreactivity for ET-1 was detected in the endothelium and adventitial fibroblasts, whilst immunoreactivity for ETA and ETB receptors was present in the endothelium, vascular smooth muscle, perivascular nerves and fibroblasts. In endothelial cells immunoreactivity to ET-1 was pronounced in the cytoplasm or on the granular endoplasmic reticulum. Similar patterns of immunolabelling were observed for ETA and ETB receptors, though cytoplasmic location of clusters of immunoprecipitate seems dominant. These results suggest that the endothelin system is present throughout the wall of the basilar artery of capybara.

Transcriptional Up-Regulation in Expression of 5-Hydroxytryptamine2A and Transcriptional Down-Regulation of Angiotensin II type 1 Receptors during Organ Culture of Rat Mesenteric Artery

The purpose of this study was to investigate in rat mesenteric artery if there is up-regulation of 5-hydroxytryptamine (5-HT) receptors and angiotensin II receptors and the potential role of protein kinase C activation in the smooth muscle cells during organ culture. Angiotensin II, 5-HT and potassium induced contraction of ring segments without endothelium, monitored by a sensitive in vitro pharmacology method. After the culture of the arterial ring segments for 24 hr, the concentration-contraction curves induced by 5-HT slightly shifted towards to the left with pEC(50) from 6.64+/-0.11 to 6.84+/-0.11 and a significant increase in E(max) from 147+/-11% to 246+/-15% (P<0.05), compared with that obtained in fresh segments. In contrast, the angiotensin II concentration-contraction curve only showed a significant decrease in E(max) from 99+/-10% to 37+/-8%. Specific antagonists for the 5-HT type 2A receptors (5-HT(2A)) and angiotensin II type 1 receptors (AT(1)) demonstrated that the contractions occurred via 5-HT(2A) and AT(1) receptors, respectively. Real-time PCR revealed that the 5-HT(2A) receptor mRNA was up-regulated in parallel with the contractile response while there was a down-regulation of AT(1) receptor mRNA. Transcriptional inhibitor actinomycin D and specific protein kinase C inhibitor Ro31-8220 demonstrated that it was a transcriptional mechanism with involvement of protein kinase C that regulated the enhanced expression of 5-HT(2A) receptors in the mesenteric artery.

Role of mitogen-activated protein kinases in endothelin ETB receptor up-regulation after organ culture of rat mesenteric artery

Organ culture of isolated arteries results in increased levels of endothelin ET(B) (ET(B)) receptor mRNA and in enhanced ET(B) receptor mediated contraction. The present study was designed to pinpoint the mitogen-activated protein kinase (MAPK) subtype involved in up-regulation of ET(B) receptors after organ culture of rat mesenteric arteries. Western blot and selective antibodies towards constitutional and phosphorylated MAPKs revealed the appearance of phosphorylated MAPK of the extracellular signal-regulated kinases (ERK) 1/2 type at 3 h of organ culture. The functional ET(B) receptor and its mRNA expression were up-regulated after 24 h of organ culture. Following incubation with the MEK 1/2 specific inhibitor SB408039 or the raf inhibitor SB386023b the up-regulation was attenuated both for ET(B) receptor responses and in ET(B) receptor mRNA expression in the vessel segments. Neither Western blot nor myograph or mRNA analysis showed involvement of the other MAPKs studied. Our results suggest that the ERK1/2 MAPKs are involved in the endothelin ET(B) receptor up-regulation following organ culture.

Receptor changes in cerebral arteries after subarachnoid haemorrhage

Subarachnoid haemorrhage (SAH), occurring with a delay of 4-10 days is linked to cerebral vasospasm (CVS), a pathological constriction of the cerebral arteries. Several agents have been suggested as being responsible - amongst these perhaps 5-hydroxytryptamine (5-HT) and endothelin-1 (ET-1) are the most prominent, given their ability to elicit powerful constriction of arteries. Investigating both 5-HT and ET receptors we observed distinct changes in the receptor phenotype after experimental SAH - namely upregulation of the ETB and 5-HT1B receptors - linked to a higher sensitivity to the endogenous agonists. This multiple receptor upregulation may explain the failure in treating CVS using single receptor antagonists, and may also significantly change our understanding of the effector mechanism behind CVS. So far only the ET and 5-HT receptors have been studied in this regard, but other receptor systems may also undergo changes.