Effect of subarachnoid hemorrhage on endothelium-dependent vasodilation

Mechanisms of cerebral vasospasm and cerebral ischaemia in subarachnoid haemorrhage

Subarachnoid haemorrhage (SAH) is a cerebrovascular emergency associated with significant morbidity and mortality. SAH is characterized by heterogeneity, interindividual variation and complexity of pathophysiological responses following extravasation of blood from cerebral circulation. The purpose of this review is to integrate previously established pre-existing factors, pathophysiological pathways and to develop a concept map of mechanisms of SAH-induced cerebral vasospasm and delayed cerebral ischaemia using a systematic approach. We conducted an extensive mapping of a hypothesized sequence of pathophysiological events. Documentation of supporting evidence was done alongside a concept map building. After finalizing the model, we conducted an analysis of the consequences and connections of pathophysiological events. We included the findings of experimental research, focusing on pathophysiological processes. We focused on SAH-induced cerebral vasospasm and delayed cerebral ischaemia as a component of cerebral injury and potential systemic consequences. SAH-induced brain injury occurs within 72 h following haemorrhage. Pathophysiology of cerebral vasospasm may include reduction in NO production, direct activation of calcium channels, upregulating genes involved with inflammation and extracellular matrix remodelling, triggering oxidative stress and free radical damage to smooth muscle and lipid peroxidation of cell membranes, cortical spreading depolarizations, sympathetic activation, finally resulting in the failure of cerebral autoregulation, microthrombosis and cerebral ischaemic injury. This cascade of events might explain why medical therapy often fails to reverse resistant cerebral vasospasm and to prevent cerebral ischaemia.

Inflammatory Pathways Following Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is an acute cerebrovascular emergency resulting from the rupture of a brain aneurysm. Despite only accounting for 5% of all strokes, SAH imposes a significant health burden on society due to its relatively young age at onset. Those who survive the initial bleed are often afflicted with severe disabilities thought to result from delayed cerebral ischemia (DCI). Consequently, elucidating the underlying mechanistic pathways implicated in DCI development following SAH remains a priority. Neuroinflammation has recently been implicated as a promising new theory for the development of SAH complications. However, despite this interest, clinical trials have failed to provide consistent evidence for the use of anti-inflammatory agents in SAH patients. This may be explained by the complexity of SAH as a plethora of inflammatory pathways have been shown to be activated in the disease. By determining how these pathways may overlap and interact, we hope to better understand the developmental processes of SAH complications and how to prevent them. The goal of this review is to provide insight into the available evidence regarding the molecular pathways involved in the development of inflammation following SAH and how SAH complications may arise as a result of these inflammatory pathways.

Mechanisms of acute brain injury after subarachnoid hemorrhage

Brain injury after subarachnoid hemorrhage (SAH) is a biphasic event with an acute ischemic insult at the time of the initial bleed and secondary events such as cerebral vasospasm 3 to 7 days later. Although much has been learned about the delayed effects of SAH, less is known about the mechanisms of acute SAH-induced injury. Distribution of blood in the subarachnoid space, elevation of intracranial pressure, reduced cerebral perfusion and cerebral blood flow (CBF) initiates the acute injury cascade. Together they lead to direct microvascular injury, plugging of vessels and release of vasoactive substances by platelet aggregates, alterations in the nitric oxide (NO)/nitric oxide synthase (NOS) pathways and lipid peroxidation. This review will summarize some of these mechanisms that contribute to acute cerebral injury after SAH.

A comparison of the effects of tirilazad on subarachnoid hemorrhage-induced blood-brain barrier permeability in male and female rats

Phase III subarachnoid hemorrhage clinical trials have shown a beneficial effect of tirilazad only in men. One explanation for the decreased efficacy in women is that women metabolize the drug up to 60% faster than men. However, it is also possible that other more subtle differences between the sexes alter the pharmacodynamic response of women to tirilazad. The purpose of the present study was to compare the efficacy of tirilazad in attenuating early post-subarachnoid hemorrhage-induced blood-brain barrier damage in the rat, a species in which single-dose metabolism of the drug is comparable between males and females. Male and female rats were treated with 0.1, 0.3, 1.0, or 3.0 mg/kg tirilazad (intravenous) 10 minutes before and 2 hours after subarachnoid hemorrhage. At 3 hours posthemorrhage, the extent of blood-brain barrier damage, as measured by Evan's blue extravasation, did not differ between male and female vehicle-treated rats. In addition, treatment with tirilazad produced a similar effect in both males and females at all doses tested. At 0.3 mg/kg, blood-brain barrier damage was reduced 43.4% in males and 48.0% in females (P</=.01 vs vehicle), at 1.0 mg/kg, 33.1% in males and 29.1% in females (P</=.05), and at 3.0 mg/kg, 28.0% in males and 23.8% in females (P=NS). The lowest dose, 0.1 mg/kg, failed to protect the blood-brain barrier in both genders. These results suggest that gender differences do not significantly effect the blood-brain barrier protective efficacy of tirilazad following subarachnoid hemorrhage in the rat.

The importance of early brain injury after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a medical emergency that accounts for 5% of all stroke cases. Individuals affected are typically in the prime of their lives (mean age 50 years). Approximately 12% of patients die before receiving medical attention, 33% within 48 h and 50% within 30 days of aSAH. Of the survivors 50% suffer from permanent disability with an estimated lifetime cost more than double that of an ischemic stroke. Traditionally, spasm that develops in large cerebral arteries 3-7 days after aneurysm rupture is considered the most important determinant of brain injury and outcome after aSAH. However, recent studies show that prevention of delayed vasospasm does not improve outcome in aSAH patients. This finding has finally brought in focus the influence of early brain injury on outcome of aSAH. A substantial amount of evidence indicates that brain injury begins at the aneurysm rupture, evolves with time and plays an important role in patients' outcome. In this manuscript we review early brain injury after aSAH. Due to the early nature, most of the information on this injury comes from animals and few only from autopsy of patients who died within days after aSAH. Consequently, we began with a review of animal models of early brain injury, next we review the mechanisms of brain injury according to the sequence of their temporal appearance and finally we discuss the failure of clinical translation of therapies successful in animal models of aSAH.

Early micro vascular changes after subarachnoid hemorrhage

During the last decade much effort has been invested in understanding the events that occur early after SAH. It is now widely accepted that these early events not only participate in the early ischemic injury but also set the stage for the pathogenesis of delayed vasospasm. That early cerebral ischemia occurs after SAH is documented in both experimental SAH and in human autopsy studies; however, angiographic evidence for vasoconstriction early after SAH is lacking and the source of early ischemic injury is therefore unclear. Recently, the cerebral microvasculature has been identified as an early target of SAH. Changes in the anatomical structure of cerebral microvessels, sufficient to cause functional deficits, are found early after experimental SAH. These changes may explain cerebral ischemia in human in the absence of angiographic evidence of large vessel vasoconstriction. This paper summarizes known alterations in cerebral microvasculature during the first 48 h after SAH.

Escape of intraluminal platelets into brain parenchyma after subarachnoid hemorrhage

Platelet aggregates are present in parenchymal vessels as early as 10 min after experimental subarachnoid hemorrhage (SAH). Structural injury to parenchymal vessel walls and depletion of collagen-IV (the major protein of basal lamina) occur in a similar time frame. Since platelets upon activation release enzymes which can digest collagen-IV, we investigated the topographic relationship between platelet aggregates, endothelium, and basal lamina after SAH produced by endovascular perforation, using triple immunofluorescence and confocal microscopy with deconvolution. The location of platelet aggregates in relation to zymography-detected active collagenase was also examined. As reported previously, most cerebral vessels profiles contained platelets aggregates at 10 min after SAH. High-resolution three-dimensional image analysis placed many platelets at the ab-luminal (basal) side of endothelium at 10 min, and others either within the vascular basal lamina or in nearby parenchyma. By 24 h post hemorrhage, large numbers of platelets had entered the brain parenchyma. The vascular sites of platelet movement were devoid of endothelium and collagen-IV. Collagenase activity colocalized with vascular platelet aggregates. Our data demonstrate that parenchymal entry of platelets into brain parenchyma begins within minutes after hemorrhage. Three-dimensional analysis suggests that platelet aggregates initiate or stimulate local disruption of endothelium and destruction of adjacent basal lamina after SAH.

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.

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.

Contribution of 5-hydroxytryptamine1B receptors and 20-hydroxyeiscosatetraenoic acid to fall in cerebral blood flow after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

This study examined the interaction between 5-hydroxytryptamine1B (5-HT1B) receptors and 20-hydroxyeiscosatetraenoic acid (20-HETE) in contributing to the acute fall in regional cerebral blood flow (rCBF) after subarachnoid hemorrhage (SAH) in rats.

METHODS

The effects of intracisternal injection of 0.3 mL of arterial blood, artificial cerebrospinal fluid, and 5-HT on rCBF and the levels of 20-HETE and 5-HT in cerebrospinal fluid were measured in rats pretreated with vehicle, a 5-HT1B receptor antagonist (isamoltane hemifumarate), or an inhibitor of the synthesis of 20-HETE (HET0016). The effects of HET0016 and isamoltane on the vasoconstrictor response and changes in [Ca2+]i to 5-HT were also studied in middle cerebral arteries and vascular smooth muscle cells isolated from these vessels.

RESULTS

20-HETE and 5-HT levels in cerebrospinal fluid rose from 172+/-10 to 629+/-44 ng/mL and from 6+/-4 to 1163+/-200 nmol/mL, respectively, after SAH. rCBF fell by 30% 10 minutes after SAH, and it remained at this level for the next 2 hours. Blockade of 5-HT1B receptors prevented the sustained fall in rCBF seen after SAH. Intracisternal injection of 5-HT mimicked SAH by increasing 20-HETE levels in cerebrospinal fluid to 475+/-94 ng/mL and reducing rCBF by 30%. Blockade of the synthesis of 20-HETE with HET0016 prevented the fall in rCBF produced by 5-HT. Isamoltane and HET0016 reduced the vasoconstrictor response of isolated MCA to 5-HT by >60% and diminished the rise in [Ca2+]i produced by 5-HT in vascular smooth muscle cells isolated from these arteries.

CONCLUSIONS

These results suggest that the release of 5-HT after SAH activates 5-HT1B receptors and the synthesis of 20-HETE and that 20-HETE contributes to the acute fall in rCBF by potentiating the vasoconstrictor response of cerebral vessels to 5-HT.

Effects of a nitric oxide donor on and correlation of changes in cyclic nucleotide levels with experimental vasospasm

OBJECTIVE

Vasospasm after subarachnoid hemorrhage (SAH) may result from hemoglobin-mediated removal of nitric oxide (NO) from the arterial wall. We tested the ability of the long-acting, water-soluble, NO donor (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-1,2-diolate (DETA/NO), delivered via continuous intracisternal infusion, to prevent vasospasm in a nonhuman primate model of SAH.

METHODS

First, vasorelaxation in response to DETA/NO was characterized in vitro by using monkey basilar artery rings under isometric tension. Next, monkeys were randomized to undergo angiography, unilateral SAH, and no treatment (SAH only, n = 4) or treatment with DETA/NO (1 mmol/L, 12 ml/d, n = 4) or decomposed DETA/NO (at the same dose, n = 4). Vasospasm was assessed by angiography, which was performed on Day 0 and Day 7. Levels of cyclic adenosine monophosphate and cyclic guanosine monophosphate (cGMP) were measured in cerebral arteries on Day 7.

RESULTS

DETA/NO produced significant relaxation of monkey arteries in vitro, which reached a maximum at concentrations of 10(-5) mol/L. In monkeys, angiography demonstrated significant vasospasm of the right intradural cerebral arteries in all three groups, with no significant difference in vasospasm among the groups (P > 0.05, analysis of variance). The ratios of cGMP or cyclic adenosine monophosphate levels in the right and left middle cerebral arteries were not different among the groups (P > 0.05, analysis of variance). There was no significant correlation between arterial cGMP contents and the severity of vasospasm.

CONCLUSION

DETA/NO did not prevent vasospasm. There was no correlation between the severity of vasospasm and cyclic adenosine monophosphate and cGMP levels in the cerebral arteries. These results suggest that events downstream of cyclic nucleotides may be abnormal during vasospasm.

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.

Acute decrease in cerebral nitric oxide levels after subarachnoid hemorrhage

Disturbances in the nitric oxide (NO) vasodilatory pathway have been implicated in acute vasoconstriction and ischemia after subarachnoid hemorrhage (SAH). The authors hypothesize that blood released during SAH leads to vasoconstriction by scavenging NO and limiting its availability. This was tested by measuring the major NO metabolites nitrite and nitrate in five different brain regions before and after experimental SAH. The basal NO metabolites levels were as follows (mean +/- SD, micromol/mg wet weight): brain stem, 0.14 +/- 0.07; cerebellum, 0.12 +/- 0.08; ventral convexity cortex, 0.22 +/- 0.15; dorsal convexity cortex, 0.16 +/- 0.11; and hippocampus, 0.26 +/- 0.17. In sham-operated animals, no effect of the nitric oxide synthase (NOS) inhibitor L(G)-nitro-L-arginine-methyl-ester (30 mg/kg) was found on NO metabolites 40 minutes after administration, but a significant decrease was seen after 120 minutes. The NO metabolites decreased significantly 10 minutes after SAH in all brain regions except for hippocampus, and recovered to control levels in cerebellum at 60 minutes and in brain stem and dorsal cerebral cortex 180 minutes after SAH, while remaining low in ventral convexity cortex. Nitrite recovered completely in all brain regions at 180 minutes after SAH, whereas nitrate remained decreased in brain stem and ventral convexity cortex. Our results indicate that SAH causes acute decreases in cerebral NO levels by a mechanism other than NOS inhibition and provide further support for the hypothesis that alterations in the NO vasodilatory pathway contribute directly to the ischemic insult after SAH.

Effects of S-nitrosoglutathione on acute vasoconstriction and glutamate release after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Subarachnoid hemorrhage (SAH) causes acute vasoconstriction that contributes to ischemic brain injury shortly after the initial bleed. It has been theorized that decreased availability of nitric oxide (NO) may contribute to acute vasoconstriction. Therefore we examined the effect of the NO donor N-nitroso glutathione (GSNO) on acute vasoconstriction and early ischemic glutamate release after experimental SAH.

METHODS

SAH was induced by the endovascular suture method in anesthetized rats. GSNO (1 micromol/L/kg, n=31) or saline (n=21) was injected 5 minutes after SAH. Sham-operated rats received GSNO (1 micromol/L/kg, n=5) 5 minutes after sham surgery. Arterial and intracranial pressures, cerebral blood flow (CBF), and extracellular glutamate release were measured serially for 60 minutes after SAH. SAH size was determined, and vascular measurements were made histologically.

RESULTS

GSNO had no effect on resting blood pressure, intracranial pressure, cerebral perfusion pressure, or CBF in sham-operated animals. However, administration of GSNO after SAH was associated with significantly increased CBF (161.6+/-26.6% versus saline 37.1+/-5.5%, 60 minutes after SAH, P<0.05), increased blood vessel diameter (internal carotid artery [ICA] 285.0+/-16.5 microm versus saline 149.2+/-14.1 microm, P<0.01), decreased vessel wall thickness (ICA12.9+/-0.7 microm versus saline 25.1+/-1.6 microm, P<0.01), and decreased extracellular glutamate levels (3315.6+/-1048.3% versus saline469. 7+/-134.3%, P<0.05). Blood pressure decreased transiently, whereas intracranial pressure, cerebral perfusion pressure, and SAH size were not affected.

CONCLUSIONS

These results suggest that GSNO can reverse acute vasoconstriction and prevent ischemic brain injury after SAH. This further implies that acute vasoconstriction contributes significantly to ischemic brain injury after SAH and is mediated in part by decreased availability of NO.

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.

Tirilazad widens the therapeutic window for riluzole-induced attenuation of progressive cortical degeneration in an infant rat model of the shaken baby syndrome

Our infant rat model of traumatic subarchnoid hemorrhage combines violent shaking and hypoxia to produce subdural hemorrhaging and progressive cortical degeneration similar to that seen in victims of the shaken baby syndrome. Anesthetized, 6-day-old male rats were subjected to one episode of shaking under hypoxic conditions. Brain histologies revealed moderate-to-severe cortical hemorrhaging at 48 h postinjury and progressive cortical degeneration, as indicated by a 15.3% and 20.2% reduction in cortical wet weight, at 7 and 14 days postinjury, respectively. The purpose of the present study was to assess the effects of two antioxidant lipid peroxidation inhibitors (tirilazad mesylate and PNU-101033E), and the glutamate release inhibitor (riluzole), upon the brain pathology seen in this model. A significant, 54.3-75.3%, reduction in cortical hemorrhaging was observed in rats that were treated with a total of three doses of tirilazad (10 mg/kg, i.p.): 10 min before or 5-30 min after injury, and again at 2 and 24 h postinjury (p < 0.01 vs. vehicle). However, treatment with tirilazad or the more potent, brain-penetrating pyrrolopyrimidine, PNU-101033E (10 min before plus 2, 24, 48, and 72 h after), did not attenuate the progressive cortical degeneration typically seen at 14 days postinjury. These results suggest that free radicals play an important role in the pathophysiology of secondary brain hemorrhaging due to shaking + hypoxia, but may not be critical in the mediation of the subsequent neurodegeneration. Rather, glutamate neurotoxicity may be a key factor here. This is suggested by our observation that the glutamate release inhibitor, riluzole, significantly reduced cortical degeneration when it was administered up to 1 h postinjury in the present model. Specifically, the cortical wet weights of rats treated with 8 mg/kg riluzole (i.p.) 10 min before or 1 h after shaking + hypoxia (and again at 24 h postinjury) were 95.3% and 97.4% of noninjured controls, respectively, at 14 days postinjury (p < 0.02 vs. vehicle). Riluzole treatment beyond 1 h (e.g., 2 or 4 h postinjury) did not reduce the neurodegeneration. Lastly, we attempted to demonstrate that the therapeutic window for riluzole-induced attenuation of cortical degeneration could be extended beyond 1 h through the use of combination therapy. In this experiment, rat pups were treated with 10 mg/kg tirilazad (i.p.) at 30 min postinjury followed by 8 mg/kg riluzole (i.p.) at 4 and 24 h postinjury. At 14 days postinjury, the cortical wet weights of these rats were 94.5% of noninjured controls, thus demonstrating significant neuroprotection (p < 0.05 vs. vehicle) and a widening of the therapeutic window from 1 to 4 h in length. These results suggest that early attenuation of free radical-induced lipid peroxidation may slow down the biochemical cascade of events related to glutamate-induced excitotoxicity and, in doing so, prolong the time during which a glutamate release inhibitor, such as riluzole, is effective.

Effects of deferoxamine and sympathectomy on endothelin-1-induced contraction and acetylcholine-induced relaxation following subarachnoid hemorrhage in carotid artery

The role of endothelium-related factors in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH) has gained interest since the discovery of EDRF and of endothelin-1 (ET-1). The effect of SAH and both treatment of deferoxamine (DFO) and sympathectomy on endothelium-dependent vasodilation and ET-1-induced vasoconstriction of isolated rabbit carotid artery was examined using an isometric tension recording method. Thirty-five rabbits were divided into four groups: control animals, 7 days after SAH, treatment with DFO after SAH for 7 days and sympathectomy after SAH. Acetylcholine (10(-8) to 10(-5) M) was used to evoke concentration-dependent vasodilation of isolated arterial rings previously contracted by 10(-6) M phenylephrine. In the animals killed 7 days after SAH, acetylcholine-induced relaxation was suppressed and the degree of relaxation of this group was 50% of the initial contractile tone in response to the 10(-5) M acetylcholine. These relaxant responses did not return to control values in carotid arteries obtained from animals treated with DFO and subjected to sympathectomy. In isolated carotid arteries, ET-1 (10(-10) to 10(-8) M) produced concentration-dependent contractions. These contractile responses were significantly enhanced in animals 7 days after SAH compared with controls and did not return to control values in carotid arteries obtained from animals both treated with DFO and sympathectomized for 7 days after SAH. The present experiments suggest that impairment of endothelium-dependent vasodilation and the hyperreactivity of ET-1 of the carotid artery as well as cerebral arteries may be involved in the pathogenesis of cerebral vasospasm. Both treatment with DFO and sympathectomy during the chronic stage for vasospasm after SAH did not affect these vascular responses of the extradural part of the carotid artery to ET-1 and acetylcholine.

Modulatory role of endothelial and nonendothelial nitric oxide in 5-hydroxytryptamine-induced contraction in cerebral arteries after subarachnoid hemorrhage

OBJECTIVE

Endothelial dysfunction is claimed to play a role in the pathogenesis of delayed cerebral vasospasm after subarachnoid hemorrhage (SAH). We have examined the effect of experimental SAH on the modulatory action of endothelial and nonendothelial nitric oxide (NO) in the contractile response of goat middle cerebral artery to 5-hydroxytryptamine (5-HT).

METHODS

We compared the 5-HT-induced contractile responses of cerebral arteries from control goats and from goats with SAH that had been experimentally induced 3 days earlier by delivery of autologous arterial blood into the subarachnoid space. Contractile responses were examined by recording the isometric tension in isolated cerebral arteries. To assess the influence of endothelium, this cell layer was mechanically removed in some of the arteria, segments (rubbed arteries) from both control goats and goats with SAH.

RESULTS

In arteries from control goats, contractile responses to 5-HT were significantly higher in rubbed arteries than in arteries with intact endothelium; 5-HT-induced contractions were significantly enhanced by a competitive inhibitor of NO synthesis, NG-nitro-l-arginine, in arteries both with and without endothelium. In arteries from goats with SAH, 5-HT contracted cerebral arteries without showing significant differences between segments with endothelium and those that had been rubbed; in both cases, 5-HT-induced contractions were significantly higher than those obtained in arteries from control goats. NG-Nitro-l-arginine significantly enhanced the contractile response to 5-HT of cerebral arteries from goats with SAH.

CONCLUSION

These results suggest that cerebral arteries after SAH exhibit hyperreactivity to 5-HT via a mechanism that involves the absence of the modulatory role of endothelial NO, that SAH does not modify the modulatory role of nonendothelial NO, and that impairment of the modulatory action of endothelial NO on vascular responses to 5-HT could contribute to the pathogenesis of cerebral vasospasm after SAH.

Effect of calcitonin gene-related peptide on delayed cerebral vasospasm after experimental subarachnoid hemorrhage in rabbits

BACKGROUND

Calcitonin gene-related peptide (CGRP) is an intrinsic vasodilatory substance contained in perivascular nerve fibers of intracranial arteries. It is suggested that CGRP plays a role in cerebral vasospasm after subarachnoid hemorrhage (SAH).

METHOD

An experimental SAH was produced by intracisternal injection of arterial blood in rabbits. The animals were treated with intrathecal administration of CGRP solution 3 days after SAH. The degree of vasospasm and the effect of CGRP were evaluated angiographically by measuring the basilar artery diameter.

RESULTS

The basilar artery constricted to 73.0% of the pre-SAH values 3 days after SAH. Fifteen minutes after injection of 10(-10) mol/kg CGRP, the basilar artery dilated to 117.1% (n = 8), which was significantly larger than 67.1% in the vehicle group (n = 8) (p < 0.01). The significant vasodilatory effect of CGRP, compared with the vehicle group, lasted for 6 hours.

CONCLUSIONS

Intrathecal administration of CGRP has therapeutic potential for treating cerebral vasospasm.

Effect of clot removal on cerebrovascular contraction after subarachnoid hemorrhage in the monkey: pharmacological study

Clot removal at early surgery has been reported to be clinically effective for the prevention of cerebral vasospasm following subarachnoid hemorrhage (SAH) due to rupture of an intracranial aneurysm. We examined the most efficacious timing of mechanical clot removal on pharmacological responses in a monkey SAH model. Cynomolgus monkeys (Macaca fascicularis) were randomized into five groups: sham-operated, clot removal in which the clot was removed 48, 72, or 96 h after SAH, and clot groups. An autologous blood clot was placed around the bilateral major cerebral arteries after craniectomy to mimic the hemorrhage. Seven days after the SAH, proximal and successively distal parts of the middle cerebral arteries were cut into rings for isometric tension measurement. The contractile responses to potassium chloride, 5-hydroxytryptamine, norepinephrine, adenosine triphosphate, prostaglandin F20, and hemoglobin were greater in the proximal parts than in the distal parts in each group. Compared with the sham-operated group, the responses of the clot-removal and clot groups to the drugs were progressively attenuated. The maximum responses to 5-hydroxytryptamine in the proximal parts and to adenosine triphosphate in the distal parts started to decrease, significantly, in the clot-removal group 48 h after SAH, while most of the responses to the other agonists began to decrease in the clot-removal groups later than 72 h after SAH. These results suggest that the attenuation of cerebrovascular contractile responses 7 days after SAH is pharmacologically inevitable, even if the clot is removed as early as 48 h after the SAH. Clot removal may thus be recommended within 48h after SAH to ameliorate the severity of cerebral vasospasm following SAH.

Functional changes in cultured strips of canine cerebral arteries after prolonged exposure to oxyhemoglobin

The present study was undertaken to determine whether oxyhemoglobin (OxyHb) is responsible for the functional alterations in the cerebral arteries observed during chronic vasospasm after subarachnoid hemorrhage. Vascular strips of canine basilar arteries were kept in organ culture for 3 days with or without repetitive exposure to OxyHb (OxyHb-treated and control strips). Contractions elicited by high levels of potassium (80 mM) and uridine 5'-triphosphate (3 x 10(-4) M) were reduced in the OxyHb-treated group in a concentration-dependent manner. The relaxations evoked by nitric oxide and 8-bromo-cyclic guanosine monophosphate (8-bromo-cGMP) were not affected. Relaxations elicited by the calcium channel blocker, diltiazem, were attenuated in the OxyHb-treated rings. When the extracellular calcium concentration ([Ca2+]e) was changed from a concentration in the external solution of 10(-8) M to 10(-3) M, myogenic tension developed. Myogenic tension, expressed as a percentage of the maximum contraction in each segment, was augmented in the OxyHb-treated group at [Ca2+]e of 10(-5) M and 10(-4) M. There were no significant differences in passive compliance of the arterial wall between the two groups. These results demonstrated that prolonged exposure to OxyHb in vitro results in a decrease in contractile capacity and an increase in sensitivity to [Ca2+]e, in agreement with previous findings in spastic arteries. By contrast, impairment of the 8-bromo-cGMP-mediated relaxation pathway and increased stiffness of the arterial wall, which have been reported to occur in spastic arteries, were not induced by prolonged exposure to OxyHb in vitro.

Effects of subarachnoid hemorrhage on vascular responses to calcitonin gene-related peptide and its related second messengers

Calcitonin gene-related peptide (CGRP) is a potent vasodilator and a primary signaling molecule in neurovascular communication. In the present study, the authors examined cerebrovascular responses to CGRP and its related second messenger systems during cerebral vasospasm induced by subarachnoid hemorrhage (SAH). Tension measurements were performed in vitro on ring strips of basilar arteries obtained from rabbits subjected to artificial SAH and from control (non-SAH) animals. In vessels from SAH animals, which were preconstricted with serotonin, the vasorelaxant response to CGRP was attenuated. Because it has been suggested that vasodilation elicited by CGRP is mediated by cyclic 3',5'-adenosine monophosphate (cAMP) and/or cyclic 3',5'-guanosine monophosphate (cGMP), the vascular effects of directly activating these second messenger systems were also examined. The relaxant effect of forskolin, which activates adenylate cyclase directly, was slightly enhanced after SAH. In contrast, the relaxant effect of nitroglycerin (GTN), which activates soluble guanylate cyclase directly, was unchanged after SAH. The attenuation of CGRP-induced vasorelaxation could be the result of a modification in its ability to stimulate the production of second messengers. Experiments testing the capacity of CGRP to elevate cAMP levels showed no significant differences between vessels from non-SAH and SAH animals. Similarly, the resting levels of cAMP and the forskolin-induced elevations of cAMP did not differ between non-SAH and SAH animals. In contrast, cGMP levels were lower in resting and CGRP-treated vessels from SAH animals than in those from non-SAH animals. No significant differences in the levels of cGMP were observed between non-SAH and SAH vessels treated with GTN. This study indicates that CGRP-induced vasodilation is attenuated during vasospasm in a rabbit model of SAH. The findings also demonstrate that vasodilatory responses mediated by cAMP and cGMP are intact, although the levels of cGMP in SAH vessels are reduced. Together, these observations suggest that an attenuation in the capacity of vessels to dilate in response to CGRP occurs during cerebral vasospasm, and this change in CGRP vasoactivity is a result of modifications prior to, or independent of, the elevation of cyclic nucleotide second messengers.

Mechanisms of cerebral vasospasm in subarachnoid haemorrhage

Cerebrovascular spasm is a slowly developing constriction of the cerebral arteries, which frequently follows subarachnoid haemorrhage and is associated with considerable morbidity and mortality. The condition has been studied by use of models of subarachnoid haemorrhage in the whole animal and examination of isolated blood vessels or vascular smooth muscle cells in culture. The condition probably arises from the action of haemoglobin released from erythrocytes trapped in the subarachnoid clots, although the mechanism of action of haemoglobin remains uncertain. Systemic pharmacotherapy to avert or reverse vasospasm is still experimental.

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.

The vascular concept of glaucoma

The regulation of ocular perfusion is different for different parts of the eye. Observations on the retina can, therefore, not be extrapolated to the optic nerve head. Extraocular vessels, especially the short posterior ciliary arteries, might play a major role in regulation of ocular circulation, but additional regulation takes place in the eye itself. Dysregulation might be transient and, thus, not necessarily present and detectable at any one examination. Older patients with arteriosclerotic vessels may behave differently in this regard than do young, healthy animals. Not only the arterial but also the venous side of the circulation may be disturbed. Disk hemorrhages can not only be a sign of damage; they can also provoke ischemia. Besides hypoxia, diseased vessel walls might play a direct role in the pathogenesis of optic nerve head cupping. Finally, a relation between vascular dysregulation and aqueous-humor dynamics is conceivable.

Endothelin and aneurysmal subarachnoid haemorrhage: a study of subarachnoid cisternal cerebrospinal fluid

Endothelin (ET) is considered one of the most potent vasoconstrictor polypeptides; several experimental studies have suggested its possible role in the pathogenesis of arterial vasospasm after subarachnoid haemorrhage (SAH). Previously reported data on plasma and CSF levels of endothelin in patients with a diagnosis of SAH have been controversial. Cisternal endothelin CSF levels and the possibility that they could be related to vasospasm and other clinical patterns of SAH were investigated. CSF samples were obtained from 55 patients admitted after angiographic diagnosis of intracranial aneurysm. Levels of ET-1 and ET-3 were measured through radio-immunoassay technique. Twelve patients who had operations for unruptured aneurysms were considered control cases; 43 patients with SAH were classified according to: Hunt and Hess grading at admission, vasospasm grading, CT classification and timing of surgery. In all 55 patients ET-1 was measured, while positive levels of ET-3 were found only in 17 cases of 48. No linear correlation was found between cisternal CSF ET-1 levels when considering time of surgery, CT classification, Hunt and Hess grading at admission, and vasospasm grading. The results of ET-3 assay should be considered with great caution because of the low percentage of positive cases. Cisternal CSF levels of ET-1 and ET-3 are not directly related to the occurrence of arterial vasospasm after the aneurysm rupture, or to other major clinical patterns of SAH; however, ET-1 expression occurs either in paraphysiological (unruptured aneurysm) or in pathological conditions (SAH). It is suggested that ET may potentiate, or may be potentiated by, other factors playing a consistent pathophysiological role in the development of vasospasm.

Impairment of anti-platelet-aggregating activity of endothelial cells after experimental subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Serial changes of anti-platelet-aggregating activity in the endothelial cells after experimental subarachnoid hemorrhage were studied in 30 feline two-hemorrhage models.

METHODS

One hour or 2, 4, 7, or 14 days after mimic subarachnoid hemorrhage, ADP (40 mg/kg) was infused into the basilar artery via the right vertebral artery to activate circulating platelets. Immediately after ADP infusion, the basilar artery was fixed by intra-arterial perfusion with 1.5% glutaraldehyde in 0.1 mol/L phosphate buffer and was removed. The luminal surface was examined under a scanning electron microscope.

RESULTS

One hour after subarachnoid hemorrhage, no platelets adhered or aggregated on the luminal surface. However, 4 to 7 days after subarachnoid hemorrhage, many platelets were observed adhering or aggregating on the luminal surface.

CONCLUSIONS

These findings suggest the impairment of anti-platelet-aggregating activity of endothelial cells after subarachnoid hemorrhage. This impairment may be involved in inducing cerebral ischemia during cerebral vasospasm by causing platelet adhesion and aggregation.

Evidence for the participation of vascular endothelium originated humoral factors to cerebral vasospasm

Vascular endothelium synthesizes mediators which either cause vasorelaxation or vasoconstriction. The purpose of this study is to investigate the role of these mediators in the pathogenesis of cerebral vasospasm. An inhibitor of endothelium-derived relaxing factor is haemoglobin; endothelium removal by triton X-100 and endothelin-1 caused narrowing in the diameter of basilar artery of the rabbit. The pathological, ultrastructural investigations and computerized tomography images are in accordance with this finding. These results indicate that not only an increase in vasoconstrictor mediator level but also the lack of endothelium-derived relaxing mediators are responsible of the spasm of the basilar artery.

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.

Triphasic response of rat intracerebral arterioles to increasing concentrations of vasopressin in vitro

To determine how vasopressin affects the vascular tone of the smaller cerebral arterioles, we carried out an in vitro study of isolated and cannulated intracerebral arterioles of rats. We found that increasing concentrations of vasopressin induced a triphasic response of vasodilation (10(-12)-10(-11) M), vasoconstriction (10(-10)-10(-8) M), and vasodilation stabilizing to control diameter (10(-7)-10(-6) M) and that the maximum constriction was twice the maximum dilation in these smaller arterioles [21.2 +/- 13.1% (mean +/- SD) decrease in diameter vs. 11.2 +/- 5.7% increased]. Pretreatment of the arterioles with NG-monomethyl-L-arginine (10(-4) M), a specific inhibitor of endothelium-derived relaxing factor, abolished the vasopressin-induced vasodilation and significantly increased the vasoconstriction. These results suggest that these arterioles were maintained in a dilated state by an endothelium-derived relaxing factor activated by vasopressin. Both vasodilation and vasoconstriction were found to be mediated through vasopressin V1 receptors in a study of arterioles pretreated with d(CH2)5Tyr(Me)arginine vasopressin (10(-6) M), a vasopressin V1 receptor antagonist. These results support the hypothesis that vasopressin may constrict smaller cerebral arterioles while simultaneously dilating larger cerebral arteries. Our results also suggest that vasopressin may aggravate cerebral ischemia in pathological conditions, such as subarachnoid hemorrhage, when the arteriolar response to vasopressin shifts from vasodilation to vasoconstriction due to increased vasopressin levels in plasma and CSF and impaired endothelium-derived relaxation.

Superselective intra-arterial infusion of papaverine for the treatment of cerebral vasospasm after subarachnoid hemorrhage

This report describes the successful treatment of cerebral vasospasm after subarachnoid hemorrhage with superselective intra-arterial infusion of papaverine hydrochloride. Thirty-seven vascular territories in 10 patients with symptomatic vasospasm were treated according to the following protocol. Percutaneous transluminal angioplasty was performed in two steps. First, a silicone balloon was used for dilation of the internal carotid artery and the proximal portions of the middle cerebral artery. A silicone leak balloon or Tracker-18 catheter was then introduced into or just proximal to the site of vasospasm not accessible to the angioplasty balloon catheter for superselective infusion of 0.2% papaverine. Thirty-four of 37 vascular territories were successfully dilated, and eight of 10 patients showed improvement in neurological function after the procedure. There were no serious side effects due to infusion of papaverine. It is essential to infuse the papaverine just proximal to the spastic vessels in order to deliver sufficient concentration of drug, and infusion should be carried out as early as possible before the artery loses its ability to return to a normal luminal size. Superselective intraarterial infusion of papaverine is an alternative method of treatment for symptomatic vasospasm.

Effect of nicardipine on basilar artery vasoactive responses after subarachnoid hemorrhage

The effect of the dihydropyridine calcium antagonist, nicardipine, on the vasoactive responses of the basilar artery was investigated after subarachnoid hemorrhage (SAH). Forty-five rabbits were separated into one control group and four groups receiving SAH (nine animals each). The SAH was induced by injecting 5 ml of autologous arterial blood into the cisterna magna. SAH animals were subjected to one of the following: 1) no treatment; 2) intravenous (i.v.) saline infusion (vehicle); 3) i.v. infusion of low-dose nicardipine (0.01 mg/kg/hr), or 4) i.v. infusion of high-dose nicardipine (0.15 mg/kg/hr). The i.v. infusions were started immediately after SAH and continued for 48 hours. Serotonin (5-HT) (10(-8) to 10(-5) mol/L) was used to evoke dose-dependent vasoconstriction of isolated rings of the basilar artery 2 days after SAH. Acetylcholine (ACh) (10(-8) to 10(-4)) and adenosine-triphosphate (ATP) (10(-8) to 10(-4) mol/L) were applied after maximal contraction with 5-HT, evoke a dose-dependent vasodilatation. Compared with controls, in animals subjected to SAH serotonin caused similar or slightly larger contractions; nicardipine infusion did not decrease the amount of contraction observed after SAH. ACh and ATP caused significantly less dilatation in animals submitted to SAH than in controls. After high-dose nicardipine, ACh- and ATP-induced dilatations were significantly more pronounced (57% and 68% of initial contractile tone) than in the other animals receiving SAH (36%-39% and 45%-55%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of vasopressin and oxytocin on canine cerebral circulation in vivo

In vivo experiments on the vasoactive effects of vasopressin and oxytocin on cerebral circulation were carried out in anesthetized dogs, using an electromagnetic flowmeter to measure vertebral blood flow and angiography to measure the internal diameter of the basilar artery. Direct bolus infusion of 1 pmol to 1 nmol of vasopressin or 10 pmol to 10 nmol of oxytocin into a femoral-vertebral artery shunt produced a dose-dependent decrease in vertebral artery blood flow without significantly affecting mean arterial blood pressure. Vasopressin was more potent than endothelin and neuropeptide Y, which have also been demonstrated to induce long-lasting decreases in vertebral artery blood flow. However, direct bolus infusion of vasopressin (100 pmol and 1 nmol) or oxytocin (1 nmol and 10 nmol) into the vertebral artery dilated major vessels including the vertebral, anterior spinal, and basilar arteries, as well as the circle of Willis and its main branches, while endothelin (1 nmol) and neuropeptide Y (5 nmol) caused no change in the diameters of major cerebral arteries. The V1 antagonist d(CH2)5tyrosine(methyl) arginine vasopressin suppressed the effects of both vasopressin and oxytocin. Vasopressin was over 10 times as potent as oxytocin in both assays. The vasodilatory effect of vasopressin, which may be mediated by an endothelium-dependent mechanism, was functionally damaged in dogs after experimental subarachnoid hemorrhage. These data suggest regional differences in the sensitivity and responsiveness of vasculature to vasopressin and oxytocin, and specifically that both peptides act through V1 receptors to decrease the resistance of large vessels and increase the resistance of small vessels.

Impairment of endothelium-dependent relaxation in human basilar artery after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The goal of this study was to determine the alterations in vascular reactivity of human basilar artery after subarachnoid hemorrhage.

METHODS

Human basilar arteries were obtained from subjects who died within 1 day after subarachnoid hemorrhage and control subjects who died from causes other than brain involvement. Basilar artery strips were suspended for isometric tension recording in Krebs-Ringer solution. Morphometric study was also carried out on paraffin-embedded sections stained with van Gieson's elastica stain of preselected sites from the basilar arteries. The intimal and medial area and the intimal index ([intimal area/area circumscribed by internal elastic lamina] x 100) were evaluated.

RESULTS

Contractile responses to KCl, norepinephrine, and 5-hydroxytryptamine did not differ between subarachnoid hemorrhage and control groups. The endothelium-dependent relaxation responses to thrombin, bradykinin, and calcium ionophore A23187 were less for the subarachnoid hemorrhage group than for the control group. However, the endothelium-independent response to sodium nitroprusside of the subarachnoid hemorrhage group did not differ from that of the control group. Morphometric measurements were comparable between the two groups.

CONCLUSIONS

These results suggest that the decreased relaxation responses to thrombin and bradykinin occur at the level of endothelial cells and not smooth muscle cells and that decreased relaxation may be involved in delayed vasospasm after subarachnoid hemorrhage. Although the decreased relaxation was observed within 1 day after subarachnoid hemorrhage, a period in which delayed spasm does not occur, this time difference may be dependent on the severity of bleeding after rupture of an aneurysm.

Preventive effect of synthetic serine protease inhibitor, FUT-175, on cerebral vasospasm in rabbits

The effect of the synthetic multiserine protease inhibitor FUT-175 on cerebral vasospasm after subarachnoid hemorrhage (SAH) was investigated in rabbits. The SAH in rabbits was simulated by a single injection of autologous arterial blood into the cisterna magna, and, for 7 days, the caliber of each basilar artery was examined several times via angiogram. In 10 SAH rabbits, the peak of the arterial narrowing was observed on Day 2. In this model, the effect of intravenous administrations of FUT-175 was examined. Twenty-seven SAH rabbits were randomly divided into three groups, and 3 doses of 1, 2, or 3 mg of FUT-175 were administered intravenously. Angiographic arterial narrowing on Day 2 in nontreated SAH rabbits (Control) was 35% compared with 21, 5, and 14% in rabbits treated with a total of 3 (Group A; n = 9), 6 (Group B; n = 13), and 9 mg (Group C; n = 5) of FUT-175, respectively. There were statistically significant differences in the arterial calibers between Group A and the Control on Days 1 and 2, between Group B and the Control from days 1 to 4, and between Group C and the Control from days 1 to 4. In three other rabbits, after vasospasm reached its maximum on Day 2, no vasodilatory effect was observed when a total of 6 mg of FUT-175 was administered intravenously. The results indicate that the inhibition of the plasma serine protease cascades at an early stage of SAH prevents the development of cerebral vasospasm.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of bilirubin on rabbit cerebral arteries in vivo and in vitro

The effect of bilirubin on vasoreactivity was examined in the exposed rabbit basilar artery (diameter, 1045 +/- 17 microns; n = 18) and its cortical branches (diameter, 265 +/- 11 microns; n = 43) in vivo. Vasoconstriction induced by uridine triphosphate (UTP; 10(-5) to 10(-3) mol/L) was observed in vivo before and after a 60-minute application of supersaturated bilirubin (10(-4) mol/L). Bilirubin was dissolved in modified artificial cerebrospinal fluid (pH 7.4) or in physiological salt solution (pH 7.6). The latter was spectrophotometrically estimated to contain a higher concentration of free bilirubin because of the formation of less colloid. After treatment with bilirubin in artificial cerebrospinal fluid, the effect was minimal in the basilar arteries (n = 7), whereas the diameter of the branches was reduced by 9.6 +/- 1.5% (n = 23) and UTP-induced vasoconstriction was potentiated. After application of bilirubin in physiological salt solution, the basilar arteries contracted slightly (-2.1 +/- 0.9%; n = 6) and the UTP-induced vasoconstriction in the branches was attenuated (n = 12). After a 60-minute incubation of basilar artery with bilirubin in physiological salt solution in vitro, isometric tension recordings showed a diminution in KCl- and UTP-induced vasoconstrictions. Acetylcholine- and sodium nitroprusside-induced relaxations were also attenuated. It is suggested that bilirubin may exert different effects depending on the size of arteries and the concentration of free bilirubin. The constrictor and potentiating effects of bilirubin could be caused by the impairment of the relaxation mechanism. When the toxic effect of bilirubin becomes severe, the constrictor mechanism is also damaged.

Clinical relevance of endothelium-derived relaxing factor (EDRF)

1. In addition to metabolic and neurohumoral factors endothelium-derived autacoids like the nitric oxide radical NO and prostacyclin are effective regulators of vascular tone and thus tissue perfusion. NO is produced in endothelial cells from L-arginine by a Ca2+/calmodulin-dependent enzyme NO synthase. In addition, the NO radical is ultimately cleaved from all nitrovasodilators and resembles their vasoactive and antiaggregatory principle, which is used under pathological conditions as substitution therapy for impaired endothelial function and autacoid production. Impaired endothelium-dependent vasomotor control has been documented in hypercholesterolaemia, atheromatosis, diabetes, hypertension, and in reperfusion damage. L-arginine supplementation is effective in a few instances.

A review of hemoglobin and the pathogenesis of cerebral vasospasm

We believe that current experimental and clinical evidence can be most satisfactorily interpreted by assuming that oxyhemoglobin is the cause of cerebral vasospasm that follows subarachnoid hemorrhage. We review the pathogenetic mechanisms by which oxyhemoglobin affects cerebral arteries. The relative importance of each of these mechanisms in the genesis of vasospasm, the biochemical pathways of oxyhemoglobin-induced smooth muscle contraction, and the intracellular actions of oxyhemoglobin on smooth muscle and on other cells in arteries are still not definitely established.

Phosphoramidon inhibits the conversion of intracisternally administered big endothelin-1 to endothelin-1

It is suggested that endothelin-1 (ET-1), a potent vasoconstrictor peptide, is involved in the pathogenesis of cerebral vasospasm following subarachnoid hemorrhage (SAH). We examined the effects of intracisternal administration of big ET-1 on the cerebral arteries in the absence or presence of pretreatment with phosphoramidon, an inhibitor of ET converting enzyme, in anesthetized dogs. After intracisternal administration of big ET-1 (10 micrograms/dog), the caliber of the basilar artery on the angiogram was decreased to about 59% of the control. This was accompanied by a marked increase in immunoreactive ET in the cerebrospinal fluid. Systemic arterial pressure was markedly elevated following big ET-1 injection. All changes induced by big ET-1 were effectively prevented with phosphoramidon. These data suggest that intracisternally administered big ET-1 is converted to ET-1 and that the generated ET-1 produces cerebral vasospasm and hypertension. A phosphoramidon-sensitive metalloproteinase appears to contribute to this conversion.

The influence of endothelium on the action of PGF2 alpha and some dihydropyridine-type calcium antagonists in porcine basilar arteries

Vascular endothelium modulates the effect of various vasoconstricting mediators as well as the affinity of dihydropyridine-type calcium entry blockers. To further investigate this influence, vasoconstriction by PGF2 alpha as opposed to KCl and the affinity of nitrendipine and some related 3-ester side-chain derivatives were determined in isolated porcine basilar arteries in the presence and in the absence of intact endothelium, as well as in the presence of methylene blue. Treatment with methylene blue or mechanical endothelial damage increased the contractile work of basilar arteries stimulated by PGF2 alpha and reduced the affinity of the dihydropyridines in such precontracted vessels. Both experimental conditions resulted in nearly the same effect. In addition, the degree of intact endothelium, as determined by substance-P-induced vasodilation, significantly correlated with the corresponding efficacy of all dihydropyridines examined. In contrast, KCl-mediated contractions remained unchanged. It is suggested that the endothelium (probably due to the production and release of endothelium-derived vasorelaxing factors, such as EDRF and/or prostacyclin) may attenuate PGF2 alpha-induced transmembrane calcium influx through receptor operated calcium channels, whereas potential operated calcium channels seems to be unaffected.

Selective attenuation by perivascular blood of prostanoid-dependent cerebrovascular dilation in piglets

Cerebral hemorrhagic insults are common in neonates. However, the consequences of intracranial blood on cerebral hemodynamics are poorly understood. We examined the effects of perivascular blood on cerebrovascular dilator responses in 29 piglets. Fresh, autologous blood (n = 15) or cerebrospinal fluid (n = 14) was placed under the dura mater over the parietal cortex, and the piglets were allowed to recover from anesthesia. One to four days later, a closed cranial window was placed over the parietal cortex and pial arteriolar responses to arterial hypercapnia (PaCO2 greater than 55 mm Hg), hemorrhagic hypotension (mean arterial blood pressure less than 35 mm Hg), or topical application of 10(-6) and 10(-4) M isoproterenol were determined. Pial arterioles in the cerebrospinal fluid group dilated 27 +/- 4% (mean +/- SEM) (n = 11) in response to hypercapnia, 26 +/- 5% (n = 9) in response to hypotension, and 26 +/- 3% in response to 10(-6) M and 40 +/- 4% in response to 10(-4) M isoproterenol (n = 11). In the group in which blood was placed on the parietal cortex, pial arterioles did not dilate significantly in response to hypercapnia (8 +/- 3%, n = 11) or hypotension (2 +/- 5%, n = 13) but dilated normally in response to isoproterenol (25 +/- 5% in response to 10(-6) M and 36 +/- 7% in response to 10(-4) M, n = 13). We conclude that prolonged contact of pial arterioles with extravascular blood selectively attenuates cerebrovascular dilation in piglets.