An in vitro comparative study of conducting vessels and penetrating arterioles after experimental subarachnoid hemorrhage in the rabbit

Correlation between Arteriole Membrane Potential and Cerebral Vasospasm after Subarachnoid Hemorrhage in Rats

Objectives

Microvessel constriction plays an important role in delayed cerebral ischemia after aneurismal subarachnoid hemorrhage (SAH). This constriction has been demonstrated in both animal model and clinical operation. The present study examined the time-related membrane potential (Em) alteration of arterioles isolated from SAH model rats and the correlation between the potential alteration of arterioles and the diameter of basilar artery.

Materials and Methods

Sprague-Dawley rats (n = 90), weighing 300 g to 350 g, were divided into t control, sham, and SAH groups. In the SAH group, blood was injected into the prechiasmatic cistern of the rats. The Em of arterioles and basilar artery diameter was measured using whole-cell clamp recordings and pressure myograph, respectively, 1, 3, 5, 7, and 14 days after SAH. The correlation was evaluated using Pearson correlation coefficients.

Results

The Em of arterioles in the SAH group depolarized on days 3, 5, and 7, and peaked on day 7. The diameters significantly decreased on days 1, 3, 5, 7, and 14, and the smallest diameter was observed on day 7. A significant correlation between potential alteration of arterioles and diameter of basilar artery was found.

Conclusions

Similar to the artery, arteriole constriction is also involved in the pathophysiological events of delayed cerebral ischemia.

Assessment of Pre- and Post-Operative Cerebral Perfusion in Anterior Circulation Intracranial Aneurysm Clipping Patients at Hospital Sungai Buloh Using CT Perfusion Scan and Correlations to Fisher, Navarro and WFNS Scores

BACKGROUND

Intracranial aneurysms may rupture and are typically associated with high morbidity and mortality, commonly due to vasospasm after rupture. Once the aneurysm ruptures, the patient's cerebral blood flow may be disturbed during the acute phase, affecting cerebral circulation and thus cerebral perfusion prior to the onset of vasospasm. Fisher and Navarro scores are used to predict vasospasm, while World Federation of Neurosurgical Societies (WFNS) scores are used to predict patient outcomes. Several score modifications are available to obtain higher sensitivity and specificity for the prediction of vasospasm development, but these scores are still unsuccessful. Alternatively, cerebral CT perfusion scan (CTP) is a non-invasive method for measuring cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) in regions of interests (ROI) to obtain the cerebral perfusion status as well as detecting vasospasm.

METHODS

A total of 30 patients' data with clipped anterior circulation intracranial aneurysms admitted to the hospital between 1 January 2013 and 30 June 2014, were collected from the hospital's electronic database. The data collected included patients' admissions demographic profiles, Fisher, Navarro and WFNS scores; and their immediate pre- and post-operative CTP parameters.

RESULTS

This study found a significant increase in post-operative MTT (pre- and post-operative MTT) were 9.75 (SD = 1.31) and 10.44 (SD = 1.56) respectively, (P < 0.001)) as well as a significant reduction in post-operative CBF (pre- and post-operative mean CBF were 195.29 (SD = 24.92) and 179.49 (SD = 31.17) respectively (P < 0.001)). There were no significant differences in CBV. There were no significant correlations between the pre- and post-operative CTP parameters and Fisher, Navarro or WFNS scores.

CONCLUSION

Despite the interest in using Fisher, Navarro and WFNS scores to predict vasospasm and patient outcomes for ruptured intracranial aneurysms, this study found no significant correlations between these scores in either pre- or post-operative CTP parameters. These results explain the disagreement in the field regarding the multiple proposed grading systems for vasospasm prediction. CTP measures more than just anatomical structures; therefore, it is more sensitive towards minor changes in cerebral perfusion that would not be detected by WFNS, Fisher or Navarro scores.

Microvascular Dysfunction and Cognitive Impairment

The impact of vascular risk factors on cognitive function has garnered much interest in recent years. The appropriate distribution of oxygen, glucose, and other nutrients by the cerebral vasculature is critical for proper cognitive performance. The cerebral microvasculature is a key site of vascular resistance and a preferential target for small vessel disease. While deleterious effects of vascular risk factors on microvascular function are known, the contribution of this dysfunction to cognitive deficits is less clear. In this review, we summarize current evidence for microvascular dysfunction in brain. We highlight effects of select vascular risk factors (hypertension, diabetes, and hyperhomocysteinemia) on the pial and parenchymal circulation. Lastly, we discuss potential links between microvascular disease and cognitive function, highlighting current gaps in our understanding.

Current management of delayed cerebral ischemia: update from results of recent clinical trials

Subarachnoid hemorrhage (SAH) accounts for 5-7% of all strokes worldwide and is associated with high mortality and morbidity. Even after surgical intervention, approximately 30% of patients develop long-term cognitive and neurological deficits that significantly affect their capacity to return to work or daily life unassisted. Much of this stems from a secondary ischemic phenomenon referred to as delayed cerebral ischemia (DCI). While DCI has been historically attributed to the narrowing of the large basal cerebral arteries, it is now recognized that numerous pathways contribute to its pathogenesis, including microcirculatory dysfunction, microthrombosis, cortical spreading depression, and early brain injury. This paper seeks to summarize some of the key pathophysiological events that are associated with poor outcome after SAH, provide a general overview of current methods of treating SAH patients, and review the results of recent clinical trials directed at improving outcome after SAH. The scientific basis of these studies will be discussed, in addition to the available results and recommendations for effective patient management. Therapeutic methods under current clinical investigation will also be addressed. In particular, the mechanisms by which they are expected to elicit improved outcome will be investigated, as well as the specific study designs and anticipated time lines for completion.

Neurovascular signaling in the brain and the pathological consequences of hypertension

The execution and maintenance of all brain functions are dependent on a continuous flow of blood to meet the metabolic needs of the tissue. To ensure the delivery of resources required for neural processing and the maintenance of neural homeostasis, the cerebral vasculature is elaborately and extensively regulated by signaling from neurons, glia, interneurons, and perivascular nerves. Hypertension is associated with impaired neurovascular regulation of the cerebral circulation and culminates in neurodegeneration and cognitive dysfunction. Here, we review the physiological processes of neurovascular signaling in the brain and discuss mechanisms of hypertensive neurovascular dysfunction.

Mechanisms of microthrombosis and microcirculatory constriction after experimental subarachnoid hemorrhage

Microcirculatory dysfunction may contribute to delayed cerebral ischemia after subarachnoid hemorrhage (SAH). This study investigated structural changes in microvessels and their relationship to brain injury after SAH. We used 15 mice (n = 5 for each group) to create sham, saline-injected (100 μl 0.9% NaCl) or SAH (100 μl autologous blood) model by injection into the prechiasmatic cistern. We sacrificed mice 2 days after surgery and examined the brains using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and immunohistochemical staining of fibrinogen. We assessed neuronal apoptosis by terminal deoxynucleotidyl transferase dUTP (deoxyuridine triphosphate) nick end labeling (TUNEL). Nitric oxide (NO) was measured with 4,5-diaminofluorescein-2-diacetate. TEM and SEM demonstrated that mice with SAH had significantly more of them arterioles with lesion characteristics consistent with microthrombi. Microthrombi number correlated with the number of apoptotic neurons and decreased NO in the brain. In conclusion, SAH causes microthrombosis and constriction of arterioles, which correlates with neuronal death and decreased NO. These data suggest NO depletion may contribute to the formation of microthrombosis and arteriolar constriction, which in turn results in neuronal cell death.

Impact of subarachnoid hemorrhage on parenchymal arteriolar function

Intracerebral or parenchymal arterioles play an important role in the regulation of both global and regional blood flow within the brain. Brain cortex lacks significant collateral sources of blood and thus is at risk if blood flow through parenchymal arterioles is restricted. Increasingly, evidence is accumulating that abnormal parenchymal arteriolar constriction contributes to the development of neurological deficits caused by subarachnoid hemorrhage (SAH). For example, parenchymal arterioles isolated from SAH model rats exhibit enhanced constriction in response to increased intravascular pressure. This increased pressure-dependent constriction or myogenic tone would result in a shift in the cerebral autoregulatory response and decreased cerebral perfusion. Here, we summarize our current knowledge regarding cellular mechanisms contributing to enhanced contractility of parenchymal arteriolar myocytes following SAH. Our studies demonstrated that SAH-induced membrane potential depolarization involving altered K(+) homeostasis leads to enhanced voltage-dependent Ca(2+) channel activity, increased smooth muscle cytosolic Ca(2+), and parenchymal arteriolar constriction. In summary, emerging evidence demonstrates that SAH can profoundly affect parenchymal arteriolar tone, promoting decreased cortical blood flow and compromised neuronal viability.

Fundamental increase in pressure-dependent constriction of brain parenchymal arterioles from subarachnoid hemorrhage model rats due to membrane depolarization

Intracerebral (parenchymal) arterioles are morphologically and physiologically unique compared with pial arteries and arterioles. The ability of subarachnoid hemorrhage (SAH) to induce vasospasm in large-diameter pial arteries has been extensively studied, although the contribution of this phenomenon to patient outcome is controversial. Currently, little is known regarding the impact of SAH on parenchymal arterioles, which are critical for regulation of local and global cerebral blood flow. Here diameter, smooth muscle intracellular Ca(2+) concentration ([Ca(2+)](i)), and membrane potential measurements were used to assess the function of intact brain parenchymal arterioles isolated from unoperated (control), sham-operated, and SAH model rats. At low intravascular pressure (5 mmHg), membrane potential and [Ca(2+)](i) were not different in arterioles from control, sham-operated, and SAH animals. However, raising intravascular pressure caused significantly greater membrane potential depolarization, elevation in [Ca(2+)](i), and constriction in SAH arterioles. This SAH-induced increase in [Ca(2+)](i) and tone occurred in the absence of the vascular endothelium and was abolished by the L-type voltage-dependent calcium channel (VDCC) inhibitor nimodipine. Arteriolar [Ca(2+)](i) and tone were not different between groups when smooth muscle membrane potential was adjusted to the same value. Protein and mRNA levels of the L-type VDCC Ca(V)1.2 were similar in parenchymal arterioles isolated from control and SAH animals, suggesting that SAH did not cause VDCC upregulation. We conclude that enhanced parenchymal arteriolar tone after SAH is driven by smooth muscle membrane potential depolarization, leading to increased L-type VDCC-mediated Ca(2+) influx.

Ultrahigh-dose intraarterial infusion of verapamil through an indwelling microcatheter for medically refractory severe vasospasm: initial experience

Object

Vasospasm is one of the leading causes of morbidity and death following aneurysmal subarachnoid hemorrhage (SAH). Many patients suffer devastating strokes despite the best medical therapy. Endovascular treatment is the last line of defense for cases of medically refractory vasospasm. The authors present a series of patients who were treated with a prolonged intraarterial infusion of verapamil through an in-dwelling microcatheter.

Methods

Over a 1-year period 12 patients with medically refractory vasospasm due to aneurysmal SAH were identified. Data were retrospectively collected, including age, sex, Hunt and Hess grade, Fisher grade, aneurysm location, aneurysm treatment, day of the onset of vasospasm, intracranial pressure, mean arterial pressures, intraarterial treatment of vasospasm, dosages and times of verapamil infusion, presence of a new ischemic area on CT scan, modified Rankin scale score at discharge and at the last clinical follow-up, and discharge status.

Results

Twenty-seven treatments were administered. Between 25 and 360 mg of verapamil was infused per vessel (average dose per vessel 164.6 mg, range of total dose per treatment 70–720 mg). Infusion times ranged from 1 to 20.5 hours (average 7.8 hours). The number of treated vessels ranged from 1 to 7 per patient. The number of treatments per patients ranged from 1 to 4. There was no treatment-related morbidity or death. Blood pressure and intracranial pressure changes were transient and rapidly reversible. Among the 36 treated vessels, prolonged verapamil infusion was completely effective in 32 cases and partially effective in 4. Only 4 vessels required angioplasty for refractory vasospasm after prolonged verapamil infusion. There was no CT scanning evidence of new ischemic events in 9 of the 12 patients treated. At last clinical follow-up 6–12 months after discharge, 8 of 11 patients had a modified Rankin Scale score ≤2.

Conclusions

Prolonged intraarterial infusion of verapamil is a safe and effective treatment for medically refractory severe vasospasm and reduces the need for angioplasty in such cases.

Leflunomide prevents vasospasm secondary to subarachnoid haemorrhage

BACKGROUND

Though cerebral vasospasm is one of the most serious complications of subarachnoid haemorrhage (SAH), its complex pathogenesis is poorly understood and available clinical treatment options are unsatisfactory. This study was designed to examine the efficacy of leflunomide, an immunomodulatory agent with inhibitory properties, on vascular smooth muscle cell proliferation and inflammation in a rabbit cerebral vasospasm model.

METHODS

Twenty-two adult New-Zealand rabbits were assigned to 4 groups: control, SAH, SAH plus vehicle, SAH plus leflunomide. Subarachnoid haemorrhage was induced by administration of 1 ml of fresh unheparinised autologous arterial blood into the cisterna magna. Oral leflunomide (2 mg/kg) or vehicle treatment was started 12 h after the induction of subarachnoid haemorrhage and administered once a day. Three days later, the animals were sacrificed and the basilar artery was examined histologically for the lumen area and the thickness of the vessel wall. Inflammatory reaction was also examined by counting white blood cells within the vessel wall by means of light microscopic examination using haematoxylin and eosin staining.

FINDINGS

Severe and moderate vasospasms were detected in the basilar artery of the SAH and SAH plus vehicle treated groups, respectively. Leflunomide effectively reduced the vasospasm of the basilar artery. Compared to the vehicle treated group, leflunomide significantly reduced the lumen area (p < 0.01) and hyperplasia of the vessel wall (p < 0.01). Although inflammatory response within the vessel wall was reduced in the leflunomide treated group, no statistical significance was found between groups (p = 0.07).

CONCLUSION

This study demonstrates for the first time that leflunomide treatment attenuates cerebral vasospasm in a rabbit SAH model while inflammatory reaction in the vessel wall is not affected. Although further studies are needed to reveal its molecular mechanisms in relieving vasospasm, leflunomide may provide a therapeutic potential for human cerebral vasospasm induced by SAH.

Severe intracranial bleedings during endovascular procedures: outcome of surgically treated patients

OBJECTIVE

Severe intracranial bleedings (SIBs) during endovascular procedures (EPs) are accompanied by acute intracranial hypertension and brain herniation signs. The purpose of this study was to determine the effectiveness of urgent surgical management and its related patient outcome in cases with such a fatal complication.

METHOD

Medical records were reviewed retrospectively for the last 750 patients treated in our department in the past 12 years with acute non-traumatic intracranial bleeding, who underwent a diagnostic or therapeutic EP. Patients with a severe intra-procedural bleeding episode undergoing urgent surgical management (within 30 minutes after bleeding) were analysed.

RESULTS

Fourteen of 750 patients with ruptured vascular malformations presented a new SIB during EP. In nine patients, this occurred during initial angiography, two during aneurysm coiling, two during balloon angioplasty and one during arteriovenous malformation (AVM) embolization. The neurological condition 6 months later was good (independents patients) in seven cases with only a mild disability in two of them. Two patients showed a severe disability. Four patients died without recovering their consciousness. One patient presented a satisfactorily course but died weeks later owing to a pulmonary embolism.

CONCLUSION

Despite the fatal spontaneous prognosis of severe intracranial bleeding occurring during endovascular diagnostic or therapeutic procedures, a favorable outcome can be expected if an appropriated treatment was set within 30 minutes of the bleeding.

Contribution of the remodeling response to cerebral vasospasm

The authors review the remodeling response of blood vessels that occurs after various injuries to arteries. The role of this response in vasospasm after subarachnoid hemorrhage (SAH) is reviewed. There is some evidence that cerebral arteries remodel after SAH in that they are less compliant and contractile than normal. Evidence for other features, such as alteration of smooth muscle phenotype, proliferation of cells and synthesis of extracellular matrix, is conflicting and requires a further study. A remodeling response probably contributes to vasospasm but the magnitude of its importance, in relation to smooth muscle contraction, which also occurs, also needs to be further defined.

PERSISTENCE OF THE NITRIC OXIDE-DEPENDENT VASODILATORPATHWAY OF CEREBRAL VESSELS AFTEREXPERIMENTAL SUBARACHNOID HEMORRHAGE

OBJECTIVE

Efficiency of the treatment of cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH) by interfering with the nitric oxide-cyclic guanosine monophospate (cGMP) pathway seems to be inconsistent. So far, it remains unclear whether or not insufficient access to the drugs or impaired reactivity of the vessels is responsible for this inconsistency. Therefore, the aim of the present investigation was to characterize this pathway on cerebral arteries during CVS.

METHODS

CVS was induced using the rat double hemorrhage model and was determined by magnetic resonance perfusion weighted imaging. Rats were sacrificed on Day 3 and Day 5 after SAH. Immunohistochemical staining of the basilar artery for endothelial nitric oxide synthases and the alpha- and beta-subunits of the soluble guanylate cyclase was performed. Basilar artery ring segments on Day 5 were used for measurement of isometric force. Concentration effect curves for acetylcholine, sodium nitroprusside, and 8-bromo-cGMP were constructed and compared by maximum effect and pD2.

RESULTS

The immunohistochemical expression of endothelial nitric oxide synthase was comparable in all groups. The soluble guanylate cyclase alpha- and beta-subunits were significantly diminished on Day 3, but recovered by Day 5. The relaxation attributable to acetylcholine and 8-bromo-cGMP was virtually identical in controls and during CVS. Relaxation attributable to sodium nitroprusside, however, was significantly enhanced after SAH (maximum effect, control: 88 +/- 12%; Day 5: 117 +/- 26%).

CONCLUSION

The present investigations suggest the persistence of endothelium-, nitric oxide-, and cGMP-dependent relaxation during CVS. Therefore, the treatment of CVS interfering with this pathway seems not to be limited by alterations inside the vessel wall.

Thromboembolism and delayed cerebral ischemia after subarachnoid hemorrhage: an autopsy study

OBJECTIVE

Recent findings have cast doubt on vasospasm as the sole cause of delayed cerebral ischemia after subarachnoid hemorrhage.

METHODS

We reviewed the medical records of 29 patients who died after subarachnoid hemorrhage. Brain sections were taken from the insula, cingulate gyrus, and hippocampus. Adjacent sections were stained with hematoxylin-eosin and immunostained for thromboemboli. The density (burden) of the latter was calculated blindly and correlated with evidence for ischemia and with the amount of subarachnoid blood.

RESULTS

There is a strong correlation between microclot burden and delayed cerebral ischemia. Patients with clinical or radiological evidence of delayed ischemia had mean microclot burdens of 10.0/cm2 (standard deviation [SD], +/-6.6); those without had mean burdens of 2.8 (SD, +/-2.6), a highly significant difference (P = 0.002). There is also significant association (P = 0.001) between microclot burden and histological evidence of ischemia, with the mean burdens being 10.9 in sections exhibiting severe ischemia and 4.1 in those in which ischemia was absent. Microclot burden is high in patients who died within 2 days of hemorrhage, decreasing on Days 3 and 4. In delayed ischemia, the numbers rise again late in the first week and remain high until after the second week. In contrast, the average clot burden is low in patients dying without developing delayed ischemia. The amount of blood on an individual slide influenced the microclot burden on that slide to a highly significant extent (P < 0.001).

CONCLUSION

Thromboembolism after subarachnoid hemorrhage may contribute to delayed cerebral ischemia, which parallels that caused by vasospasm. The pathogenesis of thromboembolism is discussed.

Endovascular treatment strategies for cerebral vasospasm

Cerebral vasospasm is a significant cause of morbidity and mortality in patients who have sustained a subarachnoid hemorrhage from aneurysm rupture. Symptomatic cerebral vasospasm is also a strong predictor of poor clinical outcome and has thus drawn a great deal of interest from cerebrovascular surgeons. Although medical management is the cornerstone of treatment for this condition, endovascular intervention may be warranted for those in whom this treatment fails and in whom symptomatic vasospasm subsequently develops. The rapid advancements in endovascular techniques and pharmacological agents used to combat this pathological state continue to offer promise in broadening the available treatment armamentarium. In this article the authors discuss the rationale and basis for using the various endovascular options for the treatment of cerebral vasospasm, and they also discuss the limitations, complications, and efficacy of these treatment strategies in regard to neurological condition and outcome.

Vasospasm as the sole cause of cerebral ischemia: how strong is the evidence?

✓ The authors review literature that challenges the view that vasospasm involving large arteries is the exclusive cause of delayed ischemic neurological deficits (DINDs) following subarachnoid hemorrhage. They discuss alternative mechanisms and review the evidence supporting a potential role for thromboembolism. They conclude that vasospasm and thromboembolism play interrelated and additive roles in the development of DINDs, and that this interaction provides opportunities for novel therapeutic approaches.

Calcium sensitivity of vasospastic basilar artery after experimental subarachnoid hemorrhage

Arteries that develop vasospasm after subarachnoid hemorrhage (SAH) may have altered contractility and compliance. Whether these changes are due to alterations in the smooth muscle cells or the arterial wall extracellular matrix is unknown. This study elucidated the location of such changes and determined the calcium sensitivity of vasospastic arteries. Dogs were placed under general anesthesia and underwent creation of SAH using the double-hemorrhage model. Vasospasm was assessed by angiography performed before and 4, 7, or 21 days after SAH. Basilar arteries were excised from SAH or control dogs ( n = 8–52 arterial rings from 2–9 dogs per measurement) and studied under isometric tension in vitro before and after permeabilization of smooth muscle with α-toxin. Endothelium was removed from all arteries. Vasospastic arteries demonstrated significantly reduced contractility to KCl with a shift in the EC50toward reduced sensitivity to KCl 4 and 7 days after SAH ( P < 0.05, ANOVA). There was reduced compliance that persisted after permeabilization ( P < 0.05, ANOVA). Calcium sensitivity was decreased during vasospasm 4 and 7 days after SAH, as assessed in permeabilized arteries and in those contracted with BAY K 8644 in the presence of different concentrations of extracellular calcium ( P < 0.05, ANOVA). Depolymerization of actin with cytochalasin D abolished contractions to KCl but failed to alter arterial compliance. In conclusion, it is shown for the first time that calcium sensitivity is decreased during vasospasm after SAH in dogs, suggesting that other mechanisms are involved in maintaining the contraction. Reduced compliance seems to be due to an alteration in the arterial wall extracellullar matrix rather than the smooth muscle cells themselves because it cannot be alleviated by depolymerization of smooth muscle actin.

Activation of Rho-associated kinase during augmented contraction of the basilar artery to serotonin after subarachnoid hemorrhage

Delayed cerebral vasospasm after subarachnoid hemorrhage (SAH) may be due, in part, to altered regulation of arterial smooth muscle contraction. Contraction of cerebral arteries to serotonin is augmented after experimental SAH. We hypothesized that activation of Rho-associated kinase (Rho kinase) contributes to augmented contraction of cerebral arteries to serotonin after SAH. Autologous arterial blood (SAH) or artificial cerebrospinal fluid (control) was injected into the cisterna magna of anesthetized rabbits. At 2 days after injection, the basilar artery was excised and isometric contraction of arterial rings was recorded. Maximum contraction of the basilar artery to serotonin was augmented about fourfold in SAH compared with control rabbits ( P < 0.01). Contraction to histamine was similar in the two groups. Fasudil hydrochloride (3 μmol/l), an inhibitor of Rho kinase, markedly attenuated serotonin-induced contraction. Fasudil had little effect on contractions induced by histamine or phorbol 12,13-dibutyrate. In addition, phosphorylation of myosin phosphatase, a major target of Rho kinase in regulation of smooth muscle contraction, in the basilar artery was examined by Western blotting. In basilar arteries of SAH, but not control, rabbits, serotonin increased phosphorylation of myosin phosphatase about twofold at Thr853 of the myosin-targeting subunit. These results suggest that enhanced activation of Rho kinase contributes to augmented contraction of the basilar artery to serotonin after SAH.

Signaling pathways for early brain injury after subarachnoid hemorrhage

Few studies have examined the signaling pathways that contribute to early brain injury after subarachnoid hemorrhage (SAH). Using a rat SAH model, the authors explored the role of vascular endothelial growth factor (VEGF) and mitogen-activation protein kinase (MAPK) in early brain injury. Male Sprague-Dawley rats (n = 172) weighing 300 to 350 g were used for the experimental SAH model, which was induced by puncturing the bifurcation of the left anterior cerebral and middle cerebral arteries. The blood-brain barrier (BBB), brain edema, intracranial pressure, and mortality were evaluated at 24 hours after SAH. The phosphorylation of VEGF and different MAPK subgroups (ERK1/2, p38, and JNK) were examined in both the cortex and the major cerebral arteries. Experimental SAH increased intracranial pressure, BBB permeability, and brain edema and produced high mortality. SAH induced phosphorylation of VEGF and MAPKs in the cerebral arteries and, to a lesser degree, in the cortex. PP1, an Src-family kinase inhibitor, reduced BBB permeability, brain edema, and mortality and decreased the phosphorylation of VEGF and MAPKs. The authors conclude that VEGF contributes to early brain injury after SAH by enhancing the activation of the MAPK pathways, and that the inhibition of these pathways might offer new treatment strategies for SAH.

In vitro effects of new generation fungal derived nitric oxide donors on rabbit basilar artery

The fungal derived nitric oxide donors, (E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409) and N-[(E)-4-ethyl-3-[(Z)-hydroxyimino]-5-nitro-3-hexen-1-yl]-3-pyridinecarboxamide (FR144420), were evaluated for the treatment and prevention of cerebral vasospasm induced by subarachnoid hemorrhage (SAH) by an in vitro study using rabbit basilar artery. The tension-relaxation of a 3 mm-long artery segment was carried out in a micro-tissue organ bath with a real-time recorder to record the tension-relaxation curve. Steady contraction of the specimens was induced by KCI (n = 12) and oxyhemoglobin (oxyHb) (n = 12). Sodium nitroprusside was used for comparison. Each of the agents was added in ascending concentration. Relaxation caused by FK409 and FR144420 was significantly greater (p < 0.05) than that by sodium nitroprusside. Relaxation effects of FK409 and FR144420 on the KCl-induced steady contraction were better than those on the oxyHb-induced contraction. FK409 and FR144420 have potential uses for the treatment and prevention of SAH-induced cerebral vasospasm.

Evaluation of the microvasculature and cerebral ischemia after experimental subarachnoid hemorrhage in dogs

OBJECT

Whether cerebral vasospasm occurs only in surface vessels or also in parenchymal arterioles is debatable. The present study was undertaken to evaluate comprehensively the microvasculature of the brainstem after experimental subarachnoid hemorrhage (SAH).

METHODS

Nine mongrel dogs of either sex, each weighing between 18 and 24 kg, underwent double blood injections spaced 48 hours apart; the injections were infused into the cisterna magna immediately after angiography of the basilar arteries (BAs). Three additional dogs assigned to a control group received no blood injections. The dogs were killed on Day 7. Axial sections obtained from the midpontine region of both control dogs and animals subjected to SAH were evaluated with respect to the morphological characteristics of vessels and neurons, and for ultrastructural changes. Severe vasospasm occurred in the BAs of all dogs subjected to SAH. Nevertheless, in these animals, the luminal areas and vessel perimeter in parenchymal arterioles, but not in parenchymal venules, were observed to have increased when compared with those of control dogs (p < 0.01, t-test). No corrugation of the internal elastic lamina was observed and smooth-muscle and endothelial cells remained normal at the ultrastructural level in the dogs with SAH.

CONCLUSIONS

In this model, vasospasm of the BAs did not extend into the region of the pons to affect the intraparenchymal arterioles. Dilation of the parenchymal arterioles might serve as compensation for reduced blood flow. Thus, no neuronal ischemia or infarction resulted in the pontine region of the brain.

Role of adenosine 5'-triphosphate in vasospasm after subarachnoid hemorrhage: human investigations

OBJECTIVE

Adenosine 5'-triphosphate (ATP) is a vasoactive compound found in high concentrations inside erythrocytes. This compound may contribute to vasospasm after subarachnoid hemorrhage (SAH). We assessed the hypothesis that ATP contributes to vasospasm in humans.

METHODS

ATP and hemoglobin concentrations were measured in cerebrospinal fluid (CSF) from humans with SAH and in blood incubated in vitro. The vasoactivity of the human CSF samples and of fractionated (fractions with molecular weight greater than or less than 10 kDa) and unfractionated blood incubated in vitro was assessed by application of samples to canine basilar artery segments under isometric tension.

RESULTS

ATP in human CSF declined within 72 hours of SAH to concentrations too low to contract cerebral arteries. Vasoactivity of human CSF correlated with the concentration of hemoglobin. The vasoactivity of incubated erythrocyte hemolysates remained high despite a decline in ATP concentrations. Fractionation of incubated erythrocyte hemolysates showed that for incubation periods up to 7 days, all vasoactivity was in a fraction of molecular weight greater than 10 kDa.

CONCLUSION

ATP is unlikely to contribute to vasospasm because the concentrations in CSF after SAH in humans are not high enough to cause vasospasm after 72 hours. The vasoactivity of erythrocyte hemolysate is not related to the ATP or ferrous hemoglobin content but may be related to the total hemoglobin content. Therefore, ATP is unlikely to be a major cause of clinically significant delayed vasospasm.

Effects of aging on cerebral vasospasm after subarachnoid hemorrhage in rabbits

BACKGROUND AND PURPOSE

The effects of aging on cerebral vasospasm after subarachnoid hemorrhage (SAH) remain to be elucidated. The aim of this study was to clarify age-related differences of vasospasm and of papaverine reactivity in the responses of basilar arteries after SAH in rabbits.

METHODS

Rabbits receiving a single injection of arterial blood into the cisterna magna were divided into 3 groups: young (2 to 3 months old), adult (6 to 9 months old), and old (20 to 40 months old). Vertebrobasilar angiograms were obtained before SAH and 1, 2, 4, and 7 days after SAH. Papaverine was administrated selectively via the vertebral artery on day 2, and serial angiography was performed for up to 2 hours. Vessel structures were assessed with light microscopy on days 1, 2, 4, and 7 after SAH and at 10, 30, and 60 minutes after papaverine infusion.

RESULTS

Mortality from SAH in old rabbits was 40%, whereas that of young and adult rabbits was 0%. Angiograms revealed that SAH induced maximal constriction of the basilar arteries on day 2 in all age groups, and the constrictions were significantly increased with age at all time points investigated. The degree of dilatation of spastic basilar arteries after intra-arterial papaverine administration significantly decreased with age. Duration of the efficacy of papaverine became significantly shorter with age. Vessel diameter returned to the preinfusion value approximately 120, 60, and 30 minutes after infusion in young, adult, and old rabbits, respectively. Light microscopy in old rabbits showed luminal narrowing and corrugation of the internal elastic lamina not only in the basilar arteries but also in small arteries and intraparenchymal arterioles.

CONCLUSIONS

This study suggests that aging increases the degree of vasospasm in rabbits. The impaired reactivity to papaverine with aging might imply the early transition of the aged vessel to the papaverine-resistant chronic stage.

Gene transfer of calcitonin gene-related peptide prevents vasoconstriction after subarachnoid hemorrhage

We sought to determine whether adenovirus-mediated gene transfer in vivo of calcitonin gene-related peptide (CGRP), a potent vasodilator, ameliorates cerebral vasoconstriction after experimental subarachnoid hemorrhage (SAH). Arterial blood was injected into the cisterna magna of rabbits to mimic SAH 5 days after injection of AdRSVCGRP (8x10(8) pfu), AdRSVbetagal (control virus), or vehicle. After injection of AdRSVCGRP, there was a 400-fold increase in CGRP in cerebrospinal fluid. Contraction of the basilar artery to serotonin in vitro was greater in rabbits after SAH than after injection of artificial cerebrospinal fluid (P<0.001). Contraction to serotonin was less in rabbits with SAH after AdRSVCGRP than after AdRSVbetagal or vehicle (P:<0.02). Basal diameter of the basilar artery before SAH (measured with digital subtraction angiogram) was 13% greater in rabbits treated with AdRSVCGRP than in rabbits treated with vehicle or AdRSVbetagal (P:<0.005). In rabbits treated with vehicle or AdRSVbetagal, arterial diameter after SAH was 25+/-3% smaller than before SAH (P<0.0005). In rabbits treated with AdRSVCGRP, arterial diameter was similar before and after SAH and was reduced by 19+/-3% (P<0.01) after intracisternal injection of CGRP-(8-37) (0.5 nmol/kg), a CGRP(1) receptor antagonist. To determine whether gene transfer of CGRP after SAH may prevent cerebral vasoconstriction, we constructed a virus with a cytomegalovirus (CMV) promoter, which results in rapid expression of the transgene product. Treatment of rabbits with AdCMVCGRP after experimental SAH prevented constriction of the basilar artery 2 days after SAH. Thus, gene transfer of CGRP prevents cerebral vasoconstriction in vivo after experimental SAH.

Intracranial aneurysms and subarachnoid hemorrhage management of the poor grade patient

Between 20 and 30% of patients who suffer cerebral aneurysm rupture are in poor clinical grade when first evaluated. Management of these patients is controversial and challenging but can be successful with an aggressive proactive approach that begins with in the field resuscitation and continues through rehabilitation. In this article we review the epidemiology, pathology and pathophysiology, clinical features, evaluation, surgical and endovascular management, critical care, cost, and outcome prediction of patients in poor clinical grade after subarachnoid hemorrhage.

Functional changes in human pial arteries (300 to 900 micrometer ID) within 48 hours of aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Animal studies of cerebral arteries 2 to 3 days after experimental subarachnoid hemorrhage (SAH) provide evidence of arterial change such as hyperresponsiveness to contractile agonists. There is evidence that small arteries, as well as those large enough to be seen on angiography, may be involved. To directly test these possibilities, the contractile and dilator responses of pial artery segments taken from patients up to 48 hours after SAH were compared with those from patients having elective surgery for an aneurysm (Clip) and with those from normal brain vessels overlying tumors (controls).

METHODS

Segments were mounted on a resistance artery myograph for measurements of wall force changes.

RESULTS

There were no differences in maximum contractility (Emax) of the 3 groups of segments. The responses of the SAH segments to K+ (30 mmol/L) were 60.7+/-4.6% of Emax (n [number of vessels]=18), which was significantly greater than those of controls (29.9+/-5% Emax) (n=20). Clip responses were the same as control. Contractions of SAH segments to norepinephrine (1 micromol/L) were 54.3+/-7.9% Emax (n=12), and these were significantly greater than those of controls (15.1+/-6.2% Emax) (n=25). All SAH segments showed spontaneous contractile activity of varying patterns. Spontaneous activity did not occur in the Clip group and occurred in only 50% of control segments. Dilation to acetylcholine was numerically less in SAH and Clip segments than in controls, but differences were not statistically significant. The change in agonist responsiveness could result from exposure to agents that damage the blood vessel wall, resulting in partial depolarization of endothelial and smooth muscle cells.

CONCLUSIONS

Small human pial arteries are hyperresponsive to contractile agents and show spontaneous contractile activity within 48 hours of SAH. Such effects could result in narrowed resistance arteries and reduction in cerebral blood flow. These effects emphasize the wisdom of early therapeutic intervention.

Adenosine triphosphate causes vasospasm of the rat femoral artery

OBJECTIVE

Adenosine 5'-triphosphate (ATP) causes vasoconstriction by activation of P2-purinoceptors on vascular smooth muscle cells. Erythrocytes contain ATP at a concentration (1.6 mmol/L) that contracts smooth muscle. Previous studies of hemoglobin solutions did not assess whether the vasoactivity was caused by ATP rather than or in addition to hemoglobin. It was hypothesized that the hemolysis of erythrocytes that occurs after subarachnoid hemorrhage releases ATP in concentrations that cause vasospasm.

METHODS

Thirty-eight rats were randomly assigned to undergo placement of one of the following compounds in a silastic elastomer cuff around each femoral artery: 1) agarose gel (n = 8); 2) dog erythrocyte hemolysate (n = 8); 3) purified human hemoglobin (Hemolink; Hemosol, Inc., Toronto, Canada; n = 8); 4) ATP (n = 8); or 5) clotted autologous blood (n = 6). The amounts of hemoglobins and adenine nucleotides in the compounds were measured by spectrophotometry and high pressure liquid chromatography. Hemolysate, purified hemoglobin, and ATP were mixed with agarose gel to create an artificial clot. Rats were killed and fixed by perfusion at physiological blood pressure 7 days after perivascular cuff and spasmogen placement. Vasospasm was assessed by image analysis of cross sections of fixed femoral arteries. Arteries were assessed for histopathological changes on 3-point scales.

RESULTS

There was significant variance in arterial diameters among groups (mean diameter +/- standard deviation: agarose gel, 0.29 +/- 0.06; purified hemoglobin, 0.28 +/- 0.04; hemolysate, 0.24 +/- 0.05; ATP, 0.25 +/- 0.05; clotted blood, 0.24 +/- 0.01; P < 0.05, analysis of variance, n = 11-20). Animals exposed to clotted blood, hemolysate that contained ATP, or ATP, developed vasospasm, whereas purified hemoglobin and agarose did not cause vasospasm. Endothelial proliferation and perivascular inflammation were more severe (P < 0.05) in arteries exposed to clotted blood, purified hemoglobin, and hemolysate.

CONCLUSION

These results suggest that ATP may be a vasospastic substance released by erythrocyte hemolysis. The concentration of ATP in impure solutions of hemoglobin is too low to account for the vasoactivity of these solutions. The discrepancy between arterial narrowing and histopathological changes suggests that either histopathological changes may not be an important correlate of arterial vasospasm or that other substances are important in vasospasm.

Role of tyrosine kinase in serotonin-induced constriction of the basilar artery in vivo

BACKGROUND AND PURPOSE

Serotonin is one of the most potent constrictors of cerebral blood vessels and is implicated in several pathological conditions, including migraine and cerebral ischemia. Recent evidence has suggested that tyrosine kinase is involved in vasocontractile responses. The objective of this study was to test the hypothesis that activation of tyrosine kinase contributes to serotonin-induced constriction of the basilar artery in vivo.

METHODS

Using a cranial window in anesthetized Sprague-Dawley rats, we examined effects of inhibitors of tyrosine kinase and tyrosine phosphatase on constrictor responses of the basilar artery to serotonin in vivo.

RESULTS

Serotonin (10(-8), 10(-7), and 10(-6) mol/L) produced constriction of the basilar artery by 12+/-2%, 27+/-2%, and 37+/-3%, respectively. Genistein (3 x 10(-6) mol/L), an inhibitor of tyrosine kinase, did not affect baseline diameter of the basilar artery but attenuated serotonin-induced vasoconstriction (P<.05 versus control responses). Daidzein, an inactive analogue of genistein, did not affect serotonin-induced constriction of the basilar artery. Tyrphostin 47 (10(-5) mol/L), another inhibitor of tyrosine kinase, also attenuated serotonin-induced vasoconstriction, and tyrphostin 63, an inactive analogue of tyrphostin 47, did not affect the vasoconstriction. Sodium orthovanadate (10(-5) mol/L), an inhibitor of tyrosine phosphatase, enhanced serotonin-induced vasoconstriction. Phorbol 12,13-dibutyrate, a direct activator of protein kinase C, also caused constriction of the basilar artery, which was not affected by genistein or sodium orthovanadate.

CONCLUSIONS

These results suggest that serotonin-induced constriction of the basilar artery is mediated, at least in part, by activation of tyrosine kinase in vivo.

Regulation of the cerebral circulation: role of endothelium and potassium channels

Several new concepts have emerged in relation to mechanisms that contribute to regulation of the cerebral circulation. This review focuses on some physiological mechanisms of cerebral vasodilatation and alteration of these mechanisms by disease states. One mechanism involves release of vasoactive factors by the endothelium that affect underlying vascular muscle. These factors include endothelium-derived relaxing factor (nitric oxide), prostacyclin, and endothelium-derived hyperpolarizing factor(s). The normal vasodilator influence of endothelium is impaired by some disease states. Under pathophysiological conditions, endothelium may produce potent contracting factors such as endothelin. Another major mechanism of regulation of cerebral vascular tone relates to potassium channels. Activation of potassium channels appears to mediate relaxation of cerebral vessels to diverse stimuli including receptor-mediated agonists, intracellular second messenger, and hypoxia. Endothelial- and potassium channel-based mechanisms are related because several endothelium-derived factors produce relaxation by activation of potassium channels. The influence of potassium channels may be altered by disease states including chronic hypertension, subarachnoid hemorrhage, and diabetes.

Responses to mechanical stimuli of isolated basilar and femoral arteries of the Rhesus monkey are different

The present study aimed to determine regional differences in diameter response to mechanical stimuli such as flow (shear stress) and transmural pressure (myogenic response) of the isolated basilar artery and femoral artery from Rhesus monkeys. Whether or not spontaneous tone developed, a transmural pressure-diameter relation was determined after the equilibration period. Vessels were then constricted with a submaximal dose of prostaglandin-F(2 alpha) (PGF(2 alpha); 1.23-2 mu M) and a flow-diameter relation (0-2,000 mu l/min) and a pressure-diameter (15-125 cm H(2)O) relation were determined. Endothelium function was tested with the calcium ionophore A-23187 (1.0 mu M). The vessels were then maximally dilated (papaverine, 100 mu M) and a passive pressure-diameter relation was determined. The responses of the basilar and the femoral arteries were markedly different. The basilar artery developed spontaneous tone, while the femoral artery did not. The basilar artery showed flow-induced constriction (P = 0.024), while the femoral artery dilated when flow was increased (P = 0.0005). The myogenic index of the two arteries during treatment with PGF(2 alpha) was not different (P = 0.49) and the strength of the myogenic response was such that the diameter of both arteries stayed constant over the pressure range studied. We conclude that the responses to mechanical stimuli of the basilar artery and the femoral artery of the Rhesus monkey are markedly different.

Calcium channels in cerebral arteries

Electrophysiological evidence shows the existence of voltage-operated Ca2+ channels of the L- and, in some cases, T- and B-, type in the smooth muscle cells of major cerebral arteries and arterioles. Current intensity through L-type Ca2+ channels is higher in cerebral than in peripheral arteries, which points to a greater dependence on extracellular Ca2+ of contractile responses in cerebral arteries. The increase in cytosolic Ca2+ concentration is the key event leading both to maintenance of basal cerebrovascular tone and to contraction of cerebral arteries in response to depolarization and agonist-receptor interaction. Such an increase results from increased transmembrane influx of Ca2+ through L-type Ca2+ channels, as well as from the release of Ca2+ from intracellular Ca2+ stores. Ca2+ entry modulators (dihydropyridines, phenylalkylamines, benzothiazepines, and diphenylpiperazines) bind to allosterically coupled sites in the Ca2+ channel, thus inhibiting (Ca2+ entry blockers) or stimulating (Ca2+ entry activators) Ca2+ influx and, therefore, contractile responses of the cerebral arteries. In vivo, Ca2+ entry blockers increase pial vascular caliber and cerebral blood flow by their direct action on the cerebroarterial wall. However, such an action also takes place on several peripheral vascular beds, which leads to hypotension. Therefore, the brain cannot be considered a "privileged" organ when the vasodilatatory action of Ca2+ entry blockers is considered. Since increased cytosolic Ca2+ concentration (and, therefore, activation of Ca2+ channels) plays a crucial role in the pathogenesis of ischemic brain damage (e.g., acute stroke and subarachnoid hemorrhage), Ca2+ entry blockers could be useful cytoprotective drugs. However, with the exception of nimodipine in the management of subarachnoid hemorrhage, clinical trials have yielded results that are not so promising as one could expect from those obtained in experimental research.

Trigeminal sensory innervation on perforators of the circle of Willis in rabbits by wheat germ agglutinin-conjugated horseradish peroxidase anterograde tracing

Distribution patterns of sensory innervation from the trigeminal ganglion to the perforators of the circle of Willis in rabbits were investigated by wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) anterograde tracing. Twenty Japanese white rabbits were anesthetized by inhaling 1% halothane. Using a microsurgical technique, 4 microliters of 2% WGA-HRP in 1 M KCl solution, colored with brilliant blue, was micro-injected into the medial part of the left trigeminal ganglion in 14 animals with a pressure injection system. Another six served as controls to exclude the possibility of labeling non-trigeminal axons. Forty-eight hours later, the perforators in the cisternal and intracerebral segments along with their parent arteries were dissected from the brain according to Dacey's dissecting technique after transcardial perfusion, reacted with the 3,3',5,5'-tetramethyl benzidine method of Mesulam. The results revealed that sensory nerves on the perforators of the circle of Willis were less densely innervated than those on their parent arteries due to the difference in diameter. The posteromedial perforating arteries arising from the P1 segment of the posterior cerebral artery to the tegmentum, posteroventral thalamus and posterior hypothalamus were more prominently and consistently innervated than other perforators. The sensory fibers were seen on the cisternal segment of the perforating arteries. A parallel or twisted pattern was found in the perforators less than 100 microns in diameter, while a meshwork pattern was visualized in the proximal part of some bigger ones. Fine sensory fibers could be traced on the perforators as small as 40 microns in diameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelins: a role in cerebrovascular disease?

Vasoactive factors produced and released by the endothelium exert a powerful influence on vascular tone in the cerebral circulation. Impaired endothelium-dependent responses, such as decreased production of endothelium-derived relaxing factors, and/or release of endothelium-derived contractile factors may give rise to different pathophysiological conditions. Among the endothelium-derived contractile factors the endothelins have recently received particular attention. Endothelin-1 is the major isoform in the endothelin family, which also includes endothelin-2 and endothelin-3. Endothelin-1 is synthesized within the endothelium of cerebral vessels, whereas both endothelin-1 and endothelin-3 in addition have been identified in neurons and glia. Recent electrophysiological work has suggested a neuromodulatory role for these peptides, but at present the general interest is mainly focused on their vasoactive role. Physiological stimuli such as hypoxia, anoxia, and hemodynamic shear stress will stimulate the endothelial endothelin production. In the brain, at least two types of specific subreceptors have been cloned; ETA receptors, exclusively associated with blood vessels and ETB receptors also found on glial, epithelial, and ependymal cells. The endothelins seem so far to be the most potent vasoconstrictors yet identified. The circulating plasma levels of immunoreactive endothelin are low. Since more than 80% of the total amount released from endothelial cells seems to be secreted towards the underlying smooth muscle, endothelins have been ascribed a local vasoregulatory role. Endothelins are believed to be involved in several of our most common cerebrovascular diseases and the present review comments on their possible pathophysiological role in subarachnoid haemorrhage, cerebral ischemia, and migraine.

Nitric oxide and the cerebral circulation

BACKGROUND

Nitric oxide (NO) is a potent vasodilator that was initially described as the mediator of endothelium-dependent relaxation (endothelium-derived relaxing factor, EDRF). It is now known that NO is produced by a variety of other cell types.

SUMMARY OF REVIEW

Endothelium produces NO (EDRF) under basal conditions and in response to a variety of vasoactive stimuli in large cerebral arteries and the cerebral microcirculation. Endothelium-dependent relaxation is impaired in the presence of several pathophysiological conditions. This impairment may contribute to cerebral ischemia or stroke. Activation of glutamate receptors appears to be a major stimulus for production of NO by neurons. Neuronally derived NO may mediate local increases in cerebral blood flow during increases in cerebral metabolism. NO synthase-containing neurons also innervate large cerebral arteries and cerebral arterioles on the brain surface. Activation of parasympathetic fibers that innervate cerebral vessels produces NO-dependent increases in cerebral blood flow. Increases in cerebral blood flow during hypercapnia also appear to be dependent on production of NO. Astrocytes may release some NO constitutively, but astrocytes and microglia can release relatively large quantities of NO after induction of NO synthase in response to endotoxin or some cytokines. Expression of inducible NO synthase, perhaps in response to local production of cytokines, may exert cytotoxic effects in brain during or after ischemia.

CONCLUSIONS

Because endothelium, neurons, and glia can all produce NO in response to some stimuli, the influence of NO on the cerebral circulation appears to be very important. Under normal conditions, constitutively produced NO influences basal cerebral vascular tone and mediates vascular responses to a diverse group of stimuli. The inducible form of NO synthase produces much greater amounts of NO that may be an important mediator of cytotoxicity in brain.

Changes in the cerebrovascular effects of endothelin-1 and nicardipine after experimental subarachnoid hemorrhage

The role of endothelium-related factors in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH) has gained interest since the discovery of endothelin-1 (ET-1). We have examined, before and after SAH, the responsiveness of the cerebrovascular bed of the goat to ET-1, the sources of Ca2+ in ET-1-induced responses, and the ability of the Ca2+ entry blocker nicardipine to counteract them. Before SAH, injection of ET-1 into the cerebral circulation increased cerebrovascular resistance, thereby producing dose-dependent reductions in cerebral blood flow (CBF), which were prevented by nicardipine. In isolated middle cerebral arteries, ET-1 induced concentration-dependent contractions, which were equally inhibited in Ca(2+)-free medium (without or with ethylene glycol tetraacetic acid) and by the Ca2+ entry blocker nicardipine. On the third day after SAH, CBF was reduced by 28% and cerebrovascular resistance increased by 39%. At the same time, both ET-1-induced reductions in CBF and the constricting effects of ET-1 in vitro were enhanced. The ability of nicardipine to increase CBF and to inhibit the effects of ET-1 was impaired as a result of reduced dependence of cerebral arteries on extracellular Ca2+. On the seventh day after SAH, CBF and cerebrovascular resistance returned to control values, and effects of ET-1 became normal. It is suggested that the hyperreactivity to ET-1 of the cerebrovascular bed induced by SAH could have a role in the development of vasospasm, which could reduce the vascular effects of Ca2+ entry blockers after SAH.

Endothelium-derived vasoactive factors and regulation of the cerebral circulation

Vasoactive factors produced and released by endothelium exert a powerful influence on vascular tone in the cerebral circulation. Endothelium-derived relaxing factor (EDRF), which has been identified as nitric oxide (NO) or an NO-containing compound, is produced under basal conditions in cerebral blood vessels. EDRF mediates endothelium-dependent relaxation in response to a number of stimuli in the cerebral circulation. The influence of NO on the cerebral circulation appears to be particularly important and complex because both neurons and glia, in addition to endothelium, produce NO in response to some stimuli. Neuronally derived NO may mediate local vasodilation in response to increased neuronal activity. In addition to EDRF, cerebral endothelium may produce other relaxing factors, including prostacyclin, endothelium-derived hyperpolarizing factor, and oxygen-derived free radicals. Several pathophysiological conditions are associated with impaired endothelium-dependent responses that may involve the decreased production of EDRF and release of endothelium-derived contracting factors, such as the cyclooxygenase products of arachidonic acid and endothelin. The release of endothelin, an extremely potent and long-lasting vasoconstrictor peptide, may contribute to vasospasm after subarachnoid hemorrhage.

Subarachnoid hemorrhage and endothelial L-arginine pathway in small brain stem arteries in dogs

BACKGROUND AND PURPOSE

Experiments were designed to determine the effect of subarachnoid hemorrhage on endothelium-dependent relaxations in small arteries of the brain stem. A "double-hemorrhage" canine model of the disease was used, and the presence of vasospasm in the basilar artery was confirmed by angiography.

METHODS

Secondary branches of both untreated basilar arteries (inner diameter, 324 +/- 11 microns; n = 12) and arteries exposed to subarachnoid hemorrhage for 7 days (inner diameter, 328 +/- 12 microns; n = 12) were dissected and mounted on glass microcannulas in organ chambers. Changes in the intraluminal diameter of pressurized arteries were measured using a video dimension analyzer.

RESULTS

In untreated arteries, 10(-11) to 10(-7) M vasopressin, 10(-10) to 10(-6) M bradykinin, and 10(-9) to 10(-6) M calcium ionophore A23187 caused endothelium-dependent relaxations. At 10(-6) and 3 x 10(-4) M the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) abolished relaxations to vasopressin and produced small but significant rightward shifts of the concentration-response curves to bradykinin and A23187. At 10(-3) M L-arginine prevented the inhibitory effect of L-NAME. Subarachnoid hemorrhage abolished relaxations to vasopressin but did not affect relaxations to bradykinin or A23187.

CONCLUSIONS

These studies suggest that in small arteries of the brain stem vasopressin causes relaxations by activation of the endothelial L-arginine pathway. This mechanism of relaxation is selectively inhibited by subarachnoid hemorrhage. Preservation of endothelium-dependent relaxations to bradykinin and A23187 is consistent with the concept that small arteries are resistant to vasospasm after subarachnoid hemorrhage.

Regulation of the cerebral circulation by endothelium

Endothelium exerts an important influence on cerebral vascular tone through the production and release of a diverse group of vasoactive factors. Relaxing factors produced by endothelium include nitric oxide (or a nitric oxide-containing compound), a hyperpolarizing factor, and prostacyclin. Endothelium-derived contracting factors include cyclooxygenase products of arachidonic acid and endothelins. Several pathophysiological conditions are associated with increased formation of endothelium-derived contracting factors. Such endothelial dysfunction in the cerebral circulation may shift the balance of vascular tone toward constriction and may potentially contribute to the onset or maintainance of cerebral ischemia and stroke.