Subarachnoid haemorrhage: what happens to the cerebral arteries?

Cerebrovascular inflammation following subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage frequently results in complications including intracranial hypertension, rebleeding and vasospasm. The extravasated blood is responsible for a cascade of reactions involving release of various vasoactive and pro-inflammatory factors (several of which are purported to induce vasospasm) from blood and vascular components in the subarachnoid space. The authors review the available evidence linking these factors to the development of inflammatory lesions of the cerebral vasculature, emphasizing: 1) neurogenic inflammation due to massive release of sensory nerve neuropeptides; 2) hemoglobin from lysed erythrocytes, which creates functional lesions of endothelial and smooth muscle cells; 3) activity, expression and metabolites of lipoxygenases cyclooxygenases and nitric oxide synthases; 4) the possible role of endothelin-1 as a pro-inflammatory agent; 5) serotonin, histamine and bradykinin which are especially involved in blood-brain barrier disruption; 6) the prothrombotic and pro-inflammatory action of complement and thrombin towards endothelium; 7) the multiple actions of activated platelets, including platelet-derived growth factor production; 8) the presence of perivascular and intramural macrophages and granulocytes and their interaction with adhesion molecules; 9) the evolution, origins, and effects of pro-inflammatory cytokines, especially IL-1, TNF-alpha and IL-6. Human and animal studies on the use of anti-inflammatory agents in subarachnoid hemorrhage include superoxide and other radical scavengers, lipid peroxidation inhibitors, iron chelators, NSAIDs, glucocorticoids, and serine protease inhibitors. Many animal studies claim reduced vasospasm, but these effects are not always confirmed in human trials, where symptomatic vasospasm and outcome are the major endpoints. Despite recent work on penetrating vessel constriction, there is a paucity of studies on inflammatory markers in the microcirculation.

Ca2+ sparks and their function in human cerebral arteries

BACKGROUND AND PURPOSE

Local Ca2+ release events (Ca2+ sparks) caused by the opening of ryanodine-sensitive Ca2+ channels in the sarcoplasmic reticulum have been suggested to oppose constriction in cerebral arteries through the activation of large-conductance Ca2+-activated K+ (BK) channels. We report the first identification and characterization of Ca2+ sparks and associated BK channel currents in smooth muscle cells isolated from human cerebral arteries.

METHODS

Membrane currents and intracellular Ca2+ were measured with the use of the patch-clamp technique and laser scanning confocal microscopy.

RESULTS

Ca2+ sparks with a peak fractional fluorescence change (F/F0) of 2.02 +/- 0.04 and size of 8.2 +/- 0.5 microm2 (n=108) occurred at a frequency of approximately 1 Hz in freshly isolated, cerebral artery myocytes from humans. At a holding potential of -40 mV, the majority of, but not all, Ca2+ sparks (61 of 85 sparks) were associated with transient BK currents. Consistent with a role for Ca2+ sparks in the control of cerebral artery diameter, agents that block Ca2+ sparks (ryanodine) or BK channels (iberiotoxin) were found to contract human cerebral arteries.

CONCLUSIONS

This study provides evidence for local Ca2+ signaling in human arterial myocytes and suggests that these events may play an important role in control of cerebral artery diameter in humans.

A single subcutaneous bolus of erythropoietin normalizes cerebral blood flow autoregulation after subarachnoid haemorrhage in rats

Systemic administration of recombinant erythropoietin (EPO) has been demonstrated to mediate neuroprotection. This effect of EPO may in part rely on a beneficial effect on cerebrovascular dysfunction leading to ischaemic neuronal damage. We investigated the in vivo effects of subcutaneously administered recombinant EPO on impaired cerebral blood flow (CBF) autoregulation after experimental subarachnoid haemorrhage (SAH). Four groups of male Sprague-Dawley rats were studied: group A, sham operation plus vehicle; group B, sham operation plus EPO; group C, SAH plus vehicle; group D, SAH plus EPO. SAH was induced by injection of 0.07 ml of autologous blood into the cisterna magna. EPO (400 iu kg(-1) s.c.) or vehicle was given immediately after the subarachnoid injection of blood or saline. Forty-eight hours after the induction of SAH, CBF autoregulatory function was evaluated using the intracarotid (133)Xe method. CBF autoregulation was preserved in both sham-operated groups (lower limits of mean arterial blood pressure: 91+/-3 and 98+/-3 mmHg in groups A and B, respectively). In the vehicle treated SAH-group, autoregulation was abolished and the relationship between CBF and blood pressure was best described by a single linear regression line. A subcutaneous injection of EPO given immediately after the induction of SAH normalized autoregulation of CBF (lower limit in group D: 93+/-4 mmHg, NS compared with groups A and B). Early activation of endothelial EPO receptors may represent a potential therapeutic strategy in the treatment of cerebrovascular perturbations after SAH.

Novel mechanisms contributing to cerebral vascular dysfunction during chronic hypertension

Chronic hypertension is a major risk factor for numerous cardiovascular disorders and is strongly associated with stroke. Hypertension alters cerebral vascular structure and may have profound deleterious effects on cerebral vascular function, the underlying mechanisms of which are still not well understood. Recent findings have led to important developments in our understanding of novel areas of cerebral vascular biology. This review briefly examines new evidence for physiologic and pathologic roles of K(+) channels, the renin-angiotensin system and reactive oxygen species, and Rho and Rho-kinase in regulation of cerebral vascular tone.

Potassium channel openers: therapeutic potential in cardiology and medicine

Potassium (K(+)) channel openers (KCOs) define a class of chemically diverse agents that share a common molecular target, the metabolism-regulated ATP-sensitive K(+) (K(ATP)) channel. In view of the unique function that K(ATP) channels play in the maintenance of cellular homeostasis, this novel class of ion channel modulators adds to existent pharmacotherapy with potential in promoting cellular protection under conditions of metabolic stress. Indeed, experimental studies have demonstrated broad therapeutic potential for KCOs, including roles as cardioprotective agents, vasodilators, bronchodilators, bladder relaxants, anti-epileptics, insulin secretagogues and promoters of hair growth. However, clinical experience with these drugs is limited and their place in patient management needs to be fully established.

Cerebrovascular dysfunction after subarachnoid haemorrhage: novel mechanisms and directions for therapy

1. When a cerebral aneurysm ruptures, bleeding and clot formation occur around the surface of the brain, including several major blood vessels. The resulting condition, known as subarachnoid haemorrhage (SAH), often results in death or severe disability and is a significant cause of stroke. Delayed cerebral vasospasm and impaired vasodilatation are critical clinical complications that occur after SAH. Mechanisms contributing to the development of vasospasm and abnormal reactivity of cerebral arteries after SAH have been intensively investigated in recent years. The present short review briefly decribes recent advances in our knowledge of two relatively novel aspects of the mechanism(s) underlying the vascular abnormalities following SAH. 2. Cerebral arteries are depolarized after SAH, possibly due to decreased activity of potassium channels in vascular muscle. Decreased basal activation of potassium channels may be due to several mechanisms, including impaired activity of nitric oxide (NO). Vasodilator drugs that produce hyperpolarization, such as potassium channel openers, appear to be particularly effective for dilating cerebral arteries after experimental SAH. 3. Subarachnoid haemorrhage often involves decreased responsiveness of cerebral arteries to NO. This could be due to impaired activity of soluble guanylate cyclase, resulting in reduced basal levels of cGMP in cerebral vessels. However, an alternative explanation is that there may be an increased rate of cGMP hydrolysis by phosphodiesterase (PDE)-V in the cerebral vascular wall and that this abnormality contributes substantially to the impairment of NO-mediated cerebral vasodilatation after SAH. In support of this proposal, vasodilator responses to NO are reported to be normalized when coadministered with a PDE-V inhibitor following experimental SAH. 4. Thus, in cerebral vascular muscle after SAH, abnormalities of vasodilator mechanisms involving potassium channel function and also NO/cGMP activity may contribute to cerebral vascular dysfunction. These mechanisms may also represent useful and novel therapeutic targets for the treatment of vasospasm.

Cell-to-cell communication via nitric oxide modulation of oscillatory Cl(-) currents in rat intact cerebral arterioles

1. Diffusion-mediated changes in ion channel function within blood vessels have not been demonstrated directly in a patch-clamp study. Here, we examined the hypothesis that endothelium-derived diffusible bioactive substances would modify endothelin-1 (ET-1)-evoked membrane currents in smooth muscle cells situated within intact arterioles. 2. In pieces of arterioles dissected from the rat cerebral pial membrane, patch electrodes were placed on single smooth muscle cells identified under the microscope. Under perforated patch-clamp conditions, ET-1 evoked an oscillatory inward current at negative potentials in such cells in the presence of the gap junction disrupter 18alpha-glycyrrhetinic acid. ET-1 also elicited an oscillation superimposed on a membrane depolarization in current-clamp mode. 3. The oscillatory current exhibited an outwardly rectifying current-voltage relationship, a sensitivity to niflumic acid, a requirement for inositol 1,4,5-trisphosphate (IP(3))- and caffeine-sensitive Ca(2+) stores and for external Ca(2+) and a rank order of anion permeabilities characteristic of Ca(2+)-activated Cl(-) currents (I(Ca(Cl))). 4. This oscillatory response was inhibited by bradykinin (an effect distinct from the electrical propagation of hyperpolarization) and this effect was attenuated by the NO-synthase inhibitor N(omega)-nitro-L-arginine and by the NO scavenger oxyhaemoglobin but not by the cyclo-oxygenease inhibitor indomethacin. 8-Bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) and nitroprusside closely mimicked the effect of bradykinin. 5. The present patch-clamp study has revealed diffusion-mediated cell-to-cell interaction in an intact blood vessel: bradykinin appears to cause NO to move from endothelium to smooth muscle, there to inhibit an ET-1-evoked oscillatory I(Ca(Cl)) via the NO-cGMP pathway.

Broad-spectrum and selective serine protease inhibitors prevent expression of platelet-derived growth factor-BB and cerebral vasospasm after subarachnoid hemorrhage: vasospasm caused by cisternal injection of recombinant platelet-derived growth factor-BB

BACKGROUND AND PURPOSE

Plasma serine protease cascade, including the complement system and thrombin, is activated in the subarachnoid space during the acute phase after subarachnoid hemorrhage (SAH). To examine the effect of protease cascade-based inflammation and subsequent vascular repair in the development of cerebral vasospasm, we examined the effect of 2 synthetic serine protease inhibitors-FUT-175, an inhibitor of thrombin and the complement system, and argatroban, a selective inhibitor of thrombin-on the development of cerebral vasospasm in a rabbit SAH model.

METHODS

One hundred Japanese White male rabbits were used in the study. The SAH was simulated by a single injection of autologous arterial blood into the cisterna magna. To evaluate the development of cerebral vasospasm, the caliber of the basilar artery was measured on x-ray film before and at 2 days after SAH. Nine groups of rabbits (n=6 each) were treated with continuous intravenous injection of FUT-175 (2.5, 5, 10, or 20 mg/d), argatroban (1.25, 2.5, or 5 mg/d), or the same amount of saline (vehicle) for 48 hours, starting 40 minutes after SAH. Two days after SAH, the expression of homodimer of platelet-derived growth factor-BB (PDGF-BB) in the basilar artery was examined with immunohistochemical techniques. In 20 normal rabbits, 5 microg of recombinant PDGF-BB or vehicle was injected into the cisterna magna, and the basilar arteries were examined on angiograms for 48 hours.

RESULTS

Significant differences were observed in the caliber of the basilar arteries between the vehicle group and the groups with the 3 larger doses of FUT-175 (vehicle, 52+/-5.0%; 5 mg, 79+/-5.7%; 10 mg, 80+/-2.5%; 20 mg, 80+/-3.7%) and between the vehicle group and the groups with the 2 larger doses of argatroban (vehicle, 52+/-6.4%; 2.5 mg, 81+/-9.0%; 5 mg, 85+/-4.1%) (P<0.05). In the histological examination, administration of effective doses of FUT-175 or argatroban suppressed the expression of PDGF-BB in the endothelial and medial smooth muscle cell layers. Exogenous PDGF-BB caused delayed and prolonged vasoconstriction on normal basilar arteries.

CONCLUSIONS

Activation of the serine protease cascade and/or thrombin after SAH was demonstrated to play an essential role in the development of cerebral vasospasm. The expression of PDGF-BB-like protein in the arterial walls correlated with the development of cerebral vasospasm. Elevated PDGF-BB level in the subarachnoid space was found to induce delayed and chronic vasoconstriction.

Acute and delayed vasoconstriction after subarachnoid hemorrhage: local cerebral blood flow, histopathology, and morphology in the rat basilar artery

The decreased local cerebral blood flow (LCBF) and cerebral ischemia that occur after subarachnoid hemorrhage (SAH) may be caused by acute and/or delayed vasospasm. In 36 Sprague-Dawley (350-450 g) rats SAH was induced by transclival puncture of the basilar artery. Mean arterial blood pressure (MABP), LCBF, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) were measured in all rats for 30 min before and 60 min after SAH was induced. One set of control (n : 7) and experimental animals (n : 7) was sacrificed after the 60 min of initial post-hemorrhage measurements were recorded. Four days after SAH induction, LCBF and MABP were measured again for 60 min in subgroups of surviving experimental rats (n : 7) and control rats (n : 7). Histopathologic and morphologic examinations of the basilar artery were performed in each subgroup. There was a sharp drop in LCBF just after SAH was induced (55.50 +/- 11.46 mlLD/min/100 g and 16.1 +/- 3.6 mlLD/min/100 g for baseline and post-SAH, respectively; p < 0.001). The flow then gradually increased but had not returned to pre-SAH values by 60 min (p < 0.05). At 4 days after SAH induction, although LCBF was lower than that observed in the control group and pre-SAH values, it was not significantly different from either of these flow rates (p > 0.05). ICP (baseline 7.05 +/- 0.4 mmHg) increased acutely to 75.2 +/- 7.1 mmHg, but returned to normal levels by 60 min after SAH. CPP (baseline 84.5 +/- 6.3 mmHg) dropped accordingly (to 18.6 +/- 3.1 mmHg), and then increased, reaching 72.2 +/- 4.9 mmHg at 60 min after SAH (p > 0.05). Examinations of the arteries revealed decreased inner luminal diameter and distortion of the elastica layer in the early stage. LCBF in nonsurviver rats (n : 8) was lower than that in the animals that survived (p < 0.01). At 4 days post-hemorrhage, the rats' basilar arteries showed marked vasculopathy. The findings showed that acute SAH alters LCBF, ICP, and CPP, and that decreased LCBF affects mortality rate. Subsequent vasculopathy occurs in delayed fashion, and this was observed at 4 days after the hemorrhage event.

Subarachnoid haemorrhage-induced sympathoexcitation in rats is reversed by bosentan or sodium nitroprusside

1. The roles played by nitric oxide (NO) and endothelin (ET) in the genesis of sympathetic nervous activation following experimental subarachnoid haemorrhage was investigated using spectral analysis of blood pressure rhythms. 2. Subarachnoid haemorrhage was induced in conscious rats by injecting 0.3 mL homologous blood via a catheter placed along the surface of the brain and directed towards the circle of Willis. Three hours after the insult and after sympathetic activation was evident, animals received either an acute injection of the ET antagonist bosentan (5 mg/kg, i.v.; n = 7), an infusion of the NO donor sodium nitroprusside (SNP; 18 microg/h; n = 7) or no treatment (n = 7). 3. Three hours following the induction of subarachnoid haemorrhage, the mid-frequency components of systolic blood pressure were markedly elevated, indicating a pronounced sympathoexcitation. However, blood pressure and heart rate levels remained unchanged at this time. In the absence of treatment, the mid-frequency components of blood pressure remained elevated for a subsequent 2 h. Treatment with a non-hypotensive dose of SNP reversed the sympathoexcitation within 1 h. Treatment with bosentan was also effective in reducing the mid-frequency oscillations in blood pressure associated with subarachnoid haemorrhage. 4. Our results indicate that subarachnoid haemorrhage is associated with an acute activation of the sympathetic nervous system. The degree of sympathoexcitation can be reversed by the use of either bosentan or SNP.

Endothelium-dependent vasoactive modulation in the ophthalmic circulation

The vascular endothelium is strategically located between the circulating blood and the vascular smooth muscle cells. Different agonists or stimuli transported by the circulating blood can trigger the endothelium to release potent relaxing (nitric oxide, prostacyclin, endothelium-derived hyperpolarizing factor) or contracting factors (endothelin, cycloxygenase products). These endothelium-derived vasoactive factors can modulate blood flow locally. Heterogeneity exists from one vascular bed to the other, or even between vessels, in the agonists able to stimulate the release of endothelium-derived vasoactive factors. In the ophthalmic circulation, nitric oxide and endothelin are strong vasoactive modulators. In many vascular diseases that are of importance in ophthalmology (hypercholesterolemia, arteriosclerosis, hypertension, diabetes, vasospastic syndrome, ischemia and reperfusion, etc) the function of the endothelium can be impaired. There exist different drugs that can modulate the vasoactive function of the vascular endothelium. In other words, it appears that the vascular endothelium plays an important role in both the physiology and pathophysiology of the regulation of blood flow. The modulation of this regulatory system by different drugs might open new therapeutical approaches to treat vascular disorders in ophthalmology.

Analysis of purine- and pyrimidine-induced vascular responses in the isolated rat cerebral arteriole

Effects of extraluminal UTP were studied and compared with vascular responses to ATP and its analogs in rat cerebral-penetrating arterioles. UTP, UDP, 2-methylthio-ATP, and alpha,beta-methylene-ATP dilated arterioles at the lowest concentration and constricted them at high concentrations. Low concentrations of ATP dilated the vessels; high concentrations caused a biphasic response, with transient constriction followed by dilation. Endothelial impairment inhibited ATP- and UTP-mediated dilation and potentiated constriction to UTP but not to ATP. ATP- and 2-methylthio-ATP- but not UTP-mediated constrictions were inhibited by desensitization with 10(-6) M alpha,beta-methylene-ATP or 3 x 10(-6) M pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS). PPADS at 10(-4) M abolished the UTP-mediated constriction and induced vasodilation in a dose-dependent manner but did not affect the dilation to ATP. These results suggest that in rat cerebral microvessels 1) ATP and 2-methylthio-ATP induce transient constriction via smooth muscle P(2X1) receptors in the cerebral arteriole, 2) UTP stimulates two different classes of P(2Y) receptors, resulting in constriction (smooth muscle P(2Y4)) and dilation (possibly endothelial P(2Y2)), and 3) ATP and UTP produce dilation by stimulation of a single receptor (P(2Y2)).

17-beta estradiol can reduce secondary ischemic damage and mortality of subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a unique disorder commonly occurring when an aneurysm ruptures, leading to bleeding and clot formation, with a higher incidence in females. To evaluate the influence of 17-beta estradiol (E2) in the outcome of subarachnoid hemorrhage, SAH was induced by endovascular puncture of the intracranial segment of internal carotid artery in 15 intact females (INT), 19 ovariectomized females (OVX), and 13 ovariectomized female rats with E2 replacement (OVX + E2). Cerebral blood flow was recorded before and after SAH. All animals were decapitated immediately after death or 24 hours after SAH for clot area analysis. Brains were sliced and stained with 2,3,5-triphenyltetrazolium chloride (TTC) for secondary ischemic lesion analysis. The cortical cerebral blood flow (CBF), which was measured by a laser-Doppler flowmeter, decreased to 29.6%+/-17.7%, 22.8%+/-8.3%, and 43.5%+/-22.9% on the ipsilateral side (P = 0.01), and decreased to 63.4%+/-14.1%, 57.4%+/-11.0%, and 66.6%+/-17.9% on the contralateral side (P = 0.26) in INT, OVX, and OVX + E2, respectively. The subcortical CBF, which were measured by the H2 clearance method, were 7.77+/-12.03, 7.80+/-8.65, and 20.58+/-8.96 mL 100 g(-1) min(-1) on the ipsilateral side (P < 0.01), and 21.53+/-2.94, 25.13+/-3.01, and 25.30+/-3.23 mL 100 g(-1) min(-1) on the contralateral side in INT, OVX, and OVX + E2, respectively. The mortality was 53.3%, 68.4%, and 15.4% in INT, OVX, and OVX + E2, respectively (P = 0.01), whereas no significant difference in clot area was noted among the groups. The secondary ischemic lesion volume was 9.3%+/-8.4%, 24.3%+/-16.3%. and 7.0%+/-6.4% in INT, OVX, and OVX + E2, respectively (P < 0.01). This study demonstrated that E2 can reduce the mortality and secondary ischemic damage in a SAH model without affecting the clot volume.

Selective effects of subarachnoid hemorrhage on cerebral vascular responses to 4-aminopyridine in rats

BACKGROUND AND PURPOSE

We postulated that some abnormalities in cerebrovascular function after subarachnoid hemorrhage (SAH) may involve underlying alterations in K(+) channel function. Thus, using pharmacological inhibitors, we assessed the influence of SAH on function of 2 types of K(+) channel in regulation of basilar artery diameter in vivo and membrane potential (E(m)) in vitro.

METHODS

Rats were injected with saline (control) or autologous blood (SAH) into the cisterna magna. Two days later, effects of vasoactive drugs on the basilar artery were examined with a cranial window preparation. Vascular responses to 4-aminopyridine (4-AP), 3-aminopyridine (3-AP), tetraethylammonium (TEA), serotonin, acetylcholine, and adenosine were compared in control and SAH rats. Additional studies using intracellular microelectrodes evaluated the effects of 4-AP and serotonin on E(m) of basilar arteries isolated from control and SAH rats.

RESULTS

Baseline artery diameter was 236+/-5 micrometer in control rats and 220+/-7 micrometer in SAH rats (P:<0. 05). 4-AP, but not 3-AP, constricted the basilar artery in control rats, and responses to 4-AP were reduced in SAH rats. Constrictor responses to TEA or serotonin were unaffected by SAH. Vasodilator responses to acetylcholine were impaired in SAH rats, whereas responses to adenosine were not different. Resting E(m) was -81+/-3 mV in control arteries and -79+/-3 mV in SAH arteries. Both 4-AP and serotonin depolarized the basilar artery, but only 4-AP-induced depolarization was impaired in SAH arteries.

CONCLUSIONS

These data suggest that 4-AP induces cerebral vasoconstriction in vivo through smooth muscle depolarization due to inhibition of voltage-dependent K(+) channels. Furthermore, function of these K(+) channels may be selectively reduced in the basilar artery after SAH and thus could contribute to cerebral vascular dysfunction.

Immune abnormalities in aneurysmal subarachnoid haemorrhage patients: relation to delayed cerebral vasospasm

Peripheral blood CD3+, CD19+, CD4+, CD8+ and CD45RO+ mononuclear cell subsets, T-cell proliferative responses to combinations of coimmobilized OKT3 antibody and an ECM protein (collagen I, collagen IV, fibronectin or elastin), and T-cell adhesion to collagen IV, fibronectin and elastin were studied in patients with aneurysmal subarachnoid haemorrhage. No significant difference was found in the major lymphocyte subsets between subarachnoid haemorrhage patients receiving no dexamethasone for brain oedema treatment and healthy blood donors. Compared with the latter, both the dexamethasone-untreated and -treated subarachnoid haemorrhage patients showed decreased relative proliferative responses of circulating T cells to OKT3 combinations with collagen IV and fibronectin, and an increased PHA-activated T-cell adhesion to elastin. CD45RO+, CD4+ and CD19+ peripheral blood cell subsets, CD4+/CD8+ cell ratio, PHA-activated T-cell adhesion to fibronectin and collagen IV, and OKT3-triggered T-cell costimulatory responses to elastin, collagen IV and fibronectin were significantly higher in subarachnoid haemorrhage patients presenting with delayed cerebral vasospasm (DCV) than in their DCV-free counterparts. The DCV-related differences in circulating lymphocyte subsets showed no apparent relationship to the glucocorticoid treatment, whereas the differences in the other indices were confined to the dexamethasone-untreated subarachnoid haemorrhage patients. The above results suggest that the CD4+/CD8+ ratio and T cell-ECM interactions play a role in the emergence of subarachnoid haemorrhage/DCV and may represent potential targets for subarachnoid haemorrhage therapy.

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.

Plasma endothelin concentrations after aneurysmal subarachnoid hemorrhage

OBJECT

The pathogenesis of cerebral vasospasm and delayed ischemia after subarachnoid hemorrhage (SAH) seems to be complex. An important mediator of chronic vasospasm may be endothelin (ET), with its powerful and long-lasting vasoconstricting activity. In this study the author investigated the correlation between serial plasma concentrations of ET and ischemic symptoms, angiographically demonstrated evidence of vasospasm, and computerized tomography (CT) findings after aneurysmal SAH.

METHODS

Endothelin-1 immunoreactivity in plasma was studied in 70 patients with aneurysmal SAH and in 25 healthy volunteers by using a double-antibody sandwich-enzyme immunoassay (immunometric) technique. On the whole, mean plasma ET concentrations in patients with SAH (mean +/- standard error of mean, 2.1 +/- 0.1 pg/ml) did not differ from those of healthy volunteers (1.9 +/- 0.2 pg/ml). Endothelin concentrations were significantly higher (p < 0.05) in patients who experienced delayed cerebral ischemia with fixed neurological deficits compared with those in other patients (post-SAH Days 0-5, 3.1 +/- 0.8 pg/ml compared with 2.1 +/- 0.2 pg/ml; post-SAH Days 6-14, 2.5 +/- 0.4 pg/ml compared with 1.9 +/- 0.2 pg/ml). Patients with angiographic evidence of severe vasospasm also had significantly (p < 0.05) elevated ET concentrations (post-SAH Days 0-5, 3.2 +/- 0.8 pg/ml; post-SAH Days 6-14, 2.7 +/- 0.5 pg/ml) as did those with a cerebral infarction larger than a lacuna on the follow-up CT scan (post-SAH Days 0-5, 3.1 +/- 0.8 pg/ml; post-SAH Days 6-14, 2.5 +/- 0.4 pg/ml) compared with other patients. Patients in whom angiography revealed diffuse moderate-to-severe vasospasm had significantly (p < 0.05) higher ET levels than other patients within 24 hours before or after angiography (2.6 +/- 0.3 compared with 1.9 +/- 0.2 pg/ml). In addition, patients with a history of hypertension or cigarette smoking experienced cerebral infarctions significantly more often than other patients, although angiography did not demonstrate severe or diffuse vasospasm more often in these patients than in others.

CONCLUSIONS

Endothelin concentrations seem to correlate with delayed cerebral ischemia and vasospasm after SAH. The highest levels of ET are predictive of the symptoms of cerebral ischemia and vasospasm, and ET may also worsen ischemia in patients with a history of hypertension. Thus, ET may be an important causal or contributing factor to vasospasm, but its significance in the pathogenesis of vasospasm remains unknown.

Brain natriuretic peptide and cerebral vasospasm in subarachnoid hemorrhage. Clinical and TCD correlations

BACKGROUND AND PURPOSE

Hyponatremia has been shown in association with cerebral vasospasm (CVS) following aneurysmal subarachnoid hemorrhage (SAH). In the past few years there has been increasing evidence that brain natriuretic peptide (BNP) is responsible for natriuresis after SAH. The purpose of the present study was to investigate the relationship between BNP plasma concentrations and CVS after aneurysmal SAH.

METHODS

BNP plasma concentrations were assessed at 4 different time periods (1 to 3 days, 4 to 6 days, 7 to 9 days, and 10 to 12 days) in 19 patients with spontaneous SAH. BNP plasma levels were investigated with respect to neurological condition, SAH severity on CT, and flow velocities measured by means of transcranial Doppler.

RESULTS

Thirteen patients had Doppler evidence of CVS; 7 of these had nonsymptomatic CVS. In 6 patients, CVS was severe and symptomatic, with delayed ischemic lesion on CT in 5 of these. CVS was severe and symptomatic in 6 patients, and delayed ischemic lesions were revealed on CT in 5 of these. BNP levels were found to be significantly elevated in SAH patients compared with control subjects (P=0.024). However, in patients without CVS or with nonsymptomatic CVS, BNP concentrations decreased throughout the 4 time periods, whereas a 6-fold increase was observed in patients with severe symptomatic CVS between the first and the third periods (P=0.0096). A similar trend in BNP plasma levels was found in patients with severe SAH compared with those with nonvisible or moderate SAH (P=0.015).

CONCLUSIONS

In conclusion, our results show that BNP plasma levels are elevated shortly after SAH, although they increase markedly during the first week in patients with symptomatic CVS. The present findings suggest that secretion of BNP secretion after spontaneous SAH may exacerbate blood flow reduction due to arterial vasospasm.

Prevention of cerebral vasospasm by a novel endothelin receptor antagonist, TA-0201

This study was designed to examine the preventive effect of a novel endothelin (ET)-receptor antagonist TA-0201 on the cerebral vasospasm in a canine double-hemorrhage model. TA-0201 (10(-9)-10(-7) M) inhibited ET-1-induced vasoconstriction in the isolated canine basilar artery without endothelium in a concentration-dependent manner. Its pA2 value was 9.2 (ET(A) antagonism). In a canine double-hemorrhage model, intravenous treatment with TA-0201 (3 mg/kg, twice a day for 7 days) ameliorated the basilar artery narrowing significantly on day 7 compared with that in nontreated dogs. The reductions of the basilar artery diameter were 26.1+/-3.9% and 40.5+/-4.1% with and without TA-0201 treatment, respectively (p<0.05). Histologic study on day 7 indicated that treatment with TA-0201 inhibited vessel-wall damage such as disintegration of endothelium architecture and degeneration of medial smooth-muscle cells. We conclude that intravenous treatment with TA-0201 prevents the development of cerebral vasospasm and accompanying pathologic changes of the vessel wall, probably through blockade of ET(A) receptors.

Impaired cerebral vasodilator responses to NO and PDE V inhibition after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is associated with impaired nitric oxide (NO)-mediated cerebral vasodilatation. We tested the hypothesis that SAH causes alterations in the production of, hydrolysis of, or responsiveness to cGMP in the rat basilar artery in vivo. Rats were injected with saline or autologous blood into the cisterna magna. Two days later, effects of vasoactive drugs on basilar artery diameter were examined using a cranial window preparation. Vasodilator responses to ACh, sodium nitroprusside (SNP), and low concentrations (</=10(-5) M) of zaprinast, an inhibitor of phosphodiesterase V (PDE V), were impaired in SAH rats (P < 0.05). In contrast, vasodilator responses to adenosine and 8-BrcGMP were similar in control and SAH rats. Vasoconstrictor responses to 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase, were unaffected by SAH. In the presence of zaprinast (10(-5)-10(-4) M), responses to ACh and SNP were equivalent in control and SAH rats. Thus an increased rate of cGMP hydrolysis by PDE V may be a major factor contributing to the impairment of NO-mediated cerebral vasodilatation after SAH.