Plasma endothelin and big endothelin concentrations and serum endothelin-converting enzyme activity following aneurysmal subarachnoid hemorrhage

OBJECT: Pathogenesis of delayed ischemia after aneurysmal subarachnoid hemorrhage (SAH) seems to be complex. An important mediator of chronic vasospasm may be endothelin (ET)-1 with its powerful and long-lasting vasoconstricting activity. In this prospective study the author investigated the correlations between serial plasma concentrations of ET-1 and big ET-1 as well as the ET-1/big ET-1 molar concentration ratio and serum endothelin-converting enzyme (ECE)-1 activity, and ischemic complications after SAH. METHODS: To measure plasma ET-1 (51 patients), big ET-1 immunoreactivity (22 patients), and serum ECE-1 activity (13 patients), blood samples were obtained on admission, in the morning after aneurysm surgery, and during the 2nd week after hemorrhage in 51 consecutive patients (28 men and 23 women, with a mean age of 50.8 years) with aneurysmal SAH. Mean plasma concentrations of ET-1 in patients with SAH (mean +/- standard deviation: on admission, 4.2 +/- 2 pg/ml; after surgery, 4.3 +/- 2.2 pg/ml; and during the 2nd week after SAH, 3.7 +/- 1.9 pg/ml) differed from those in healthy volunteers (2.9 +/- 1.2 pg/ml; p < 0.01). Plasma concentrations of ET-1 and big ET-1 as well as the ET-1/big ET-1 ratio did not change significantly with elapsed time following SAH; however, serum ECE-1 activity during the 2nd week after SAH was higher in patients with SAH than that in controls (162 +/- 43 compared with 121 +/- 56 pg/ml, respectively; p = 0.028). Plasma ET-1 concentrations (p < 0.05) and the ET-1/big ET-1 ratios (p = 0.063) were higher but plasma big ET-1 concentrations were lower (p < 0.05) in patients who experienced symptomatic delayed cerebral ischemia, compared with other patients with SAH. In addition, in cases in which follow-up computerized tomography scans or magnetic resonance images demonstrated permanent ischemic lesions attributable to vasospasm, patients had higher ET-1 concentrations than did other patients with SAH. CONCLUSIONS: The plasma ET-1 concentration correlates with delayed cerebral ischemia after SAH, suggesting that an increased ET conversion rate in the endothelium predicts ischemic symptoms. Increased serum ECE-1 activity during the 2nd week may reflect the severity of endothelial injury to cerebral arteries.     

Cerebrovascular characterization of clazosentan, the first nonpeptide endothelin receptor antagonist clinically effective for the treatment of cerebral vasospasm. Part I: inhibitory effect on endothelin(A) receptor-mediated contraction

OBJECT: The central role of endothelin (ET)-1 in the development of cerebral vasospasm after subarachnoid hemorrhage is indicated by the successful treatment of this vasospasm in several animal models by using selective ET(A) receptor antagonists. Clazosentan is a selective ET(A) receptor antagonist that provides for the first time clinical proof that ET-1 is involved in the pathogenesis of cerebral vasospasm. The aim of the present investigation was, therefore, to define the pharmacological properties of clazosentan that affect ET(A) receptor-mediated contraction in the cerebrovasculature. METHODS: Isometric force measurements were performed in rat basilar artery (BA) ring segments with (E+) and without (E-) endothelial function. Concentration effect curves (CECs) were constructed by cumulative application of ET-1 or big ET-1 in the absence or presence of clazosentan (10(-9), 10(-8), and 10(-7) M). The inhibitory potency of clazosentan was determined by the value of the affinity constant (pA2). The CECs for contraction induced by ET-1 and big ET-1 were shifted to the right in the presence of clazosentan in a parallel dose-dependent manner, which indicates competitive antagonism. The pA2 values for ET-1 were 7.8 (E+) and 8.6 (E-) and the corresponding values for big ET-1 were 8.6 (E+) and 8.3 (E-). CONCLUSIONS: The present data characterize clazosentan as a potent competitive antagonist of ET(A) receptor-mediated constriction of the cerebrovasculature by ET-1 and its precursor big ET-1. These functional data may also be used to define an in vitro profile of an ET receptor antagonist with a high probability of clinical efficacy.     

Cerebrovascular characterization of clazosentan, the first nonpeptide endothelin receptor antagonist shown to be clinically effective for the treatment of cerebral vasospasm. Part II: effect on endothelin(B) receptor-mediated relaxation

OBJECT: The disturbed balance between nitric oxide and endothelin (ET)-1 in the cerebrovasculature seems to play a major role in the development of cerebral vasospasm after subarachnoid hemorrhage. Endothelin-1 represents the contractile part in this balance. In addition to the prevailing ET(A) receptor-dependent contractile effect, ET-1 also has ET(B) receptor-mediated vasodilatory attributes. The aim of the present study was to define the actual selectivity of clazosentan, the first putative highly ET(A) receptor-selective antagonist clinically proven to be effective in the treatment of vasospasm in the cerebrovasculature. METHODS: Rat basilar artery ring segments with endothelial function were used for the measurement of isometric force. Concentration effect curves were constructed by cumulative application of sarafotoxin S6c, ET-1, or big ET-1 in the presence or absence of clazosentan (10(-9) to 10(-6) M) after a precontraction was induced by prostaglandin F2alpha. The inhibition by clazosentan was estimated by the value of the affinity constant (pA2). The relaxation induced by sarafotoxin S6c, ET-1, and big ET-1 was inhibited in a competitive manner by clazosentan, yielding pA2 values of 7.1, 6.7, and 6.5, respectively. The selectivity to the ET(A) receptor in the cerebrovascular system was approximately two logarithmic units. CONCLUSIONS: The present investigation shows a competitive inhibition of ET(B) receptor-mediated relaxation in cerebral vessels by clazosentan in therapeutically relevant concentrations. Thus, additional clinical trials should be undertaken to evaluate clazosentan concentrations in cerebrospinal fluid. Furthermore, the present data may be taken to describe the pharmacological properties for an ET receptor antagonist specifically tailored for the treatment of pathological conditions of impaired cerebral blood flow.     

Attenuation of hemolysate-induced cerebrovascular endothelial cell injury and of production of endothelin-1 and big endothelin-1 by an endothelin-converting enzyme inhibitor

BACKGROUND: Endothelin-1 (ET-1) is a potent and long-acting vasoconstrictive peptide that has been implicated in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH). ET-1 has been shown to be present in the cerebrospinal fluid of patients after SAH, and substances produced during hemolysis of subarachnoid blood clots are believed to be responsible for stimulating the production of ET-1. The biosynthesis of ET-1 is a multi-step process, involving the conversion of the relatively inactive precursor big ET-1 to the mature peptide by endothelin converting enzyme (ECE), a metalloprotease. Consequently, ECE inhibitors are expected to suppress the biosynthesis of ET-1 and reduce the pathologic impact resulting from overproduction of this peptide. The purpose of the present study was to investigate the effects of an ECE inhibitor, CGS 26303, on hemolysate-induced injury of cerebral vessel endothelial cells as well as the production of ET-1 from these cells. METHODS: Different doses of CGS 26303 and hemolysate were added to the culture medium for 48 hours. Cell injury was assessed by cell morphology and density, while the productions of ET-1 and big ET-1 were determined by radioimmunoassays. RESULTS: Hemolysate alone increased the levels of ET-1 and big ET-1 in culture medium and caused substantial cell loss. Treatment with CGS 26303 inhibited the hemolysate-induced increases in the levels of ET-1 and big ET-1 and reduced endothelial cell injury. The protective effects of CGS 26303 were modest when this inhibitor was added simultaneously with hemolysate, but were prominent and dose-dependent when the inhibitor was given 30 minutes before the addition of hemolysate. CONCLUSION: These results suggest that overproduction of ET-1 contributes significantly to hemolysate-induced damage to cerebrovascular endothelial cells.     

Interactions between vasoconstrictors in isolated human cerebral arteries

Summary This study investigates whether different endogeneous vasoconstrictors exert synergistic effects in isolated human cerebral arteries, because potentiation of contractile effects may play a role in the pathogenesis of cerebral vasospasm. Isolated human pial arteries obtained from macroscopically intact tissue during brain tumour operations were mounted onto a wire myograph. Concentration-response curves of 5-hydroxytryptamine (5-HT) were constructed in the absence and presence of threshold concentrations of the thromboxane A₂ (TXA)-analog U46619, and endothelin-1 (ET-1). Threshold concentrations of U46619 markedly enhanced the maximum contractile effect of 5-HT. The response to 5-HT Threshold concentrations of ET-1 increased the maximum response to 5-HT, and markedly shifted the dose-response curve to the left. Even after washout of ET-1, the dose-response curve of 5-HT remained shifted to the left. The increase of the contractile effect of 5-HT in the presence of U46619 did not correlate with the relaxant action of the endothelium-dependent vasodilator carbachol. Thus, synergism between contractile substances such as 5-HT, U46619, or ET-1 is seen in human cerebral arteries, and responses to 5-HT are potentiated even after washout of ET-1 and U46619. The potentiation does not depend on the endothelial function. We conclude that synergistic responses between endogeneous vasoconstrictors such as 5-HT, TXA and ET-1 may be involved in the pathogenesis of cerebral vasospasm after subarachnoid haemorrhage.     

Endothelin-1 concentration increases in the cerebrospinal fluid in cerebral vasospasm caused by subarachnoid hemorrhage

BACKGROUND: Endothelin-1 (ET-1) was originally identified as a potent vasoconstrictor peptide. Numerous reports have suggested its roles in various disorders. Although there is a great deal of evidence establishing the relationship between ET-1 and cerebral vasospasm in animals, this relationship still remains to be clarified in humans. METHODS: The concentration of ET-1 in cerebrospinal fluid (CSF) was measured by radioimmunoassay in 23 subarachnoid hemorrhage patients. CSF samples were collected every 10 days after surgery from the cisternal drainage tube. RESULTS: Initial concentrations of ET-1 in the CSF collected the first day after operation were all increased compared with the control CSF. In seven of the eight vasospasm patients, the concentrations of ET-1 had increased before the observation of vasospasm and then decreased before the disappearance of the vasospasm. In 13 out of the 15 patients without vasospasm, the concentrations of ET-1 in CSF decreased with time. CONCLUSION: We confirmed that the concentration of ET-1 in CSF increased before the onset of cerebral vasospasm caused by subarachnoid hemorrhage. The ET-1 concentration in the CSF could be a useful marker to detect cerebral vasospasm after subarachnoid hemorrhage.     

Sustained arterial narrowing after prolonged exposure to perivascular endothelin

OBJECTIVE: The vasoconstrictor peptide endothelin-1 (ET-1) produces narrowing of cerebral arteries and has been implicated in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage. Little is known, however, regarding the physiological consequences of prolonged exposure of arterial wall to ET-1. METHODS: In 30 rats, normal saline or 10(-8) mol/h of ET-1 was continuously applied for 3 or 5 days to the adventitial surface of the femoral artery in a Silastic cuff via an osmotic infusion pump. Vessels were examined for histopathological changes and luminal narrowing during ET-1 infusion (3 or 5 d) or at intervals from 2 to 9 days after infusion was stopped. RESULTS: Marked arterial constriction (30-40% arterial diameter reduction) was present during continuous ET-1 infusion for 3 or 5 days. For both 3- and 5-day ET-1 infusions, significant reduction in arterial cross sectional area persisted up to 4 days after cessation of infusion, after which normal caliber returned. In arteries with persistent luminal narrowing after cessation of ET-1 infusion, light microscopic findings revealed morphological changes in the vessel wall similar to those observed in cerebral vasospasm after subarachnoid hemorrhage, with apparent increased collagen deposition in media and adventitia. CONCLUSION: Continuous infusion of ET-1 produces reversible arterial narrowing that persists beyond the usual interval of physiological effect for this agent. Prolonged arterial constriction may produce physiological changes in arterial wall that act to maintain a narrowed lumen.     

Inhibition of endothelin-converting enzyme activity in the rabbit basilar artery

OBJECTIVE: Endothelin (ET)-1 may be involved in the regulation of cerebrovascular resistance under pathological conditions, most notably during the development of vasospasm after subarachnoid hemorrhage. Blocking ET-converting enzyme activity may be a promising approach to the prevention of cerebral vasospasm after subarachnoid hemorrhage. METHODS: In this study, the effects of several putative ET-converting enzyme inhibitors were investigated after intracisternal application in rabbits, to inhibit basilar artery contractions induced by big ET-1 (2 x 10(-6) mol/L). RESULTS: In the group pretreated with [D-Val22]big ET-1[16-38] (2 x 10(-5) mol/L) (n = 8), the angiographically measured diameter of the basilar artery changed from 0.63 +/- 0.12 mm to 0.66 +/- 0.12 mm. In the control group (n = 8), the diameter of the basilar artery decreased from 0.71 +/- 0.13 mm to 0.57 +/- 0.15 mm. These results corresponded to an increase in vessel diameter of 5 +/- 10% in the treatment group and a decrease in vessel diameter of 20 +/- 16% in the control group (P = 0.014). In the group pretreated with captopril (2 x 10(-4) mol/L) (n = 8), the angiographically measured diameter of the basilar artery changed from 0.64 +/- 0.11 mm to 0.71 +/- 0.10 mm. These results corresponded to an increase in vessel diameter of 14 +/- 19% in the treatment group, compared with a decrease in vessel diameter of 20 +/- 16% in the control group (P = 0.014). CONCLUSION: These results demonstrate that [D-Val22]big ET-1[16-38] and captopril act as highly potent ET-converting enzyme inhibitors, affecting big ET-1-induced contraction of the rabbit basilar artery.     

[D-Val22]big ET-1[16–38] inhibits endothelin-converting enzyme activity: a promising concept in the prevention of cerebral vasospasm

The aim of this study was to investigate whether the blocking of endothelin-converting enzyme (ECE) activity offers a new approach to inhibiting the development of cerebral vasospasm after subarachnoid hemorrhage (SAH) by preventing transformation of big endothelin-1 (big ET-1) to vasoactive endothelin-1 (ET-1). The effect of potential ECE inhibitors was determined in vitro by measurement of isometric contractions, induced by big ET-1, in isolated rat basilar arteries. Intact and de-endothelialized endothelium (E+ and E-, respectively) segments were examined after preincubation with the putative ECE inhibitors: phosphoramidon (10^–4 M), and [²²D-Val]big ET-1[16–38] (10^–5 M and 10^–6 M). Additionally, the effect of [D-Val²²]big ET-1[16–38] was investigated in rabbits after intracisternal application in order to inhibit the contraction of the basilar artery induced by (2×10^–6 M) big ET-1. Application of 10^–4-M phosphoramidon resulted in a statistically significant decrease in big ET-1-induced contraction in E+ and E- segments; 10^–5-M and 10^–6-M [²²D-Val]big ET-1[16–38] in E- segments produced no statistically significant effect. The application of 10^–6-M [²²D-Val]big ET-1[16–38] in E+ segments caused increased contractions, as shown by the shift to the left of the concentration-effect curve (CEC). In the rabbit group pretreated with [D-Val²²]big ET-1[16–38] (2×10^–5 M) (n=8), the angiographically measured diameter of the basilar artery increased from 0.63±0.12 mm to 0.66±0.12 mm. In the control group (n=8), this diameter decreased from 0.71±0.13 mm to 0.57±0.15 mm. This corresponded to an increase in vessel diameter of 5.24±9.89% in the treatment group and a decrease of 19.54±15.81% in the control group (P=0.002). The present study indicates the existence of functional ECE activity in rat basilar artery, which differs in the endothelium and the smooth muscle layer. These results demonstrate that [D-Val²²]big ET-1[16–38] has a potent ECE-inhibitory effect, preventing cerebral vasospasm in rabbit basilar artery by inhibiting the transformation of big ET-1 to vasoactive ET-1 after intracisternal application in vivo, whereas no inhibitory effect was detectable in rat basilar artery in vitro. Therefore, further studies of the biochemical nature of cerebrovascular ECE activity are required.     

Effect of delayed cerebral vasospasm on cerebrovascular endothelin A receptor expression and function

OBJECT: The key role in the development of cerebral vasospasm after subarachnoid hemorrhage (SAH) is increasingly assigned to endothelin (ET)-1. Constriction of the cerebrovasculature by ET-1 is mainly mediated by the ET(A) receptor but is putatively altered during the development of cerebral vasospasm. Therefore, the aim in the present study was to characterize these alterations, with the emphasis on the ET(A) receptor. METHODS: Cerebral vasospasm was induced using the rat double-hemorrhage model and proven by perfusion weighted magnetic resonance imaging. Rats were killed on Day 5 after SAH, and immunohistochemical staining for ET(A), receptors was performed. The isometric force of basilar artery ring segments with (E+, control group) and without (E-, SAH group) endothelial function was measured. Concentration effect curves (CECs) for ET-1 were constructed by cumulative application in the absence and presence of the selective ET(A) receptor antagonist clazosentan (10(-8) or 10(-7) M). RESULTS: The CEC for E+ segments was significantly shifted to the left after SAH by a factor of 3.7, whereas maximum contraction was unchanged. In E- segments, the CECs were not shifted during cerebral vasospasm but the maximum contraction was significantly enhanced. The inhibitory potency of clazosentan yielded a pA2 value of 8.6 +/- 0.2. Immunohistochemical staining of the smooth-muscle layer showed no significant increase of ET(A) receptor expression, but positive staining occurred in the endothelial space after SAH. CONCLUSIONS: The present data indicate an enhanced contractile effect of the smooth-muscle ET(A) receptors in cases of cerebral vasospasm. The inhibitory potency of clazosentan on this contraction is increased. Furthermore, some evidence for an ET(A) receptor and an endothelium-dependent vasoactive effect after SAH is provided.     

Effect of endothelin-converting enzyme inhibitors on big endothelin-1 induced contraction in isolated rat basilar artery

Summary.  Introduction: The aim of this study was to investigate whether blocking functional endothelin-converting enzyme (ECE) activity may offer a new approach to inhibit the development of cerebral vasopasm after subarachnoid hemorrhage (SAH) by preventing transformation of big Endothelin-1 (big ET-1) to vasoactive Endothelin-1 (ET-1).  Methods: In vitro, the effect of potential ECE inhibitors was determined by measurement of isometric contractions, induced by big ET-1, in isolated rat basilar arteries. Endothelium intact (E+) and de-endothelialized (E−) segments were examined after pre-incubated with the putative ECE inhibitors: Phosphoramidon (10⁻⁴ M), Captopril (10⁻³ M and 10⁻⁴ M) and [²²D-Val] big ET-1 (16–38) (10⁻⁵ M and 10⁻⁶ M).  Results: Application of 10⁻⁴ M Phosphoramidon resulted in a statistically significant decrease in big ET-1 induced contraction in endothelium intact (E+) and de-endothelialized (E−) segments; 10⁻³ M Captopril in E− segments caused a statistically significant inhibitory effect; 10⁻⁴ M and 10⁻³ M Captopril in E+ segments showed no statistically significant effect; 10⁻⁵ M and 10⁻⁶ M [²²D-Val] big ET-1 (16–38) in E− segments produced no statistically significant effect. The application of 10⁻⁶ M [²²D-Val] big ET-1 (16–38) in E+ segments caused increased contractions as shown by the shift to the left of the concentration-effect curve (CEC).  Conclusion: The present study indicates the existence of functional ECE activity in rat basilar artery, which is different in the endothelium and the smooth muscle layer. This ECE-activity could be inhibited by Captopril and Phosporamidon, suggesting a potency for prevention and therapy of cerebral vasospasm. However, the structural analogue of big ET-1, [²²D-Val] big ET-1 (16–38), was ineffective in reducing big ET-1 induced vasoconstriction and rather increased contraction in E+ vessels. Therefore further studies of the biochemical nature of the functional relevant cerebrovascular ECE activity are required for better understanding and development of other efficient ECE inhibitors. Published online October 31, 2002 Correspondence: Michael Zimmermann M.D., Ph.D., Department of Neurosurgery, University of Frankfurt/Main, Schleusenweg 2-16, 60528 Frankfurt, Germany.     

Subarachnoid hemorrhage as a cause of an adaptive response in cerebral arteries

OBJECT: It is not known whether the factors responsible for vasospasm after subarachnoid hemorrhage (SAH) cause the cerebral arteries to be narrowed independent of the subarachnoid blood clot or whether the continued presence of clot is required for the entire time of vasospasm. The authors undertook the present study to investigate this issue. METHODS: To distinguish between these possibilities, bilateral SAH was induced in monkeys. The diameters of the monkeys' cerebral arteries were measured on angiograms obtained on Days 0 (the day of SAH), 1, 3, 5, 7, and 9. The subarachnoid blood clot was removed surgically on Day 1, 3, or 5 or, in control animals, was not removed until the animals were killed on Day 7 or 9. The concentrations of hemoglobins and adenosine triphosphate (ATP), substances believed to cause vasospasm, were measured in the removed clots and the contractile activity of the clots was measured in monkey basilar arteries in vitro. If the clot was removed 1 or 3 days after placement, vasospasm was significantly diminished 4 days after clot removal. Clot removal on Day 5 had no marked effect on vasospasm. There was a significant decrease over time in hemoglobin and ATP concentrations and in the contractile activity of the clots, although substantial hemoglobin and contractile activity was still present on Day 7. CONCLUSIONS: The authors infer from these results that vasospasm requires the presence of subarachnoid blood for at least 3 days, whereas by Day 5 vasospasm is less dependent on subarachnoid blood clot. Because the clot still contains substantial amounts of hemoglobin and contractile activity after 5 days, there may be an adaptive response in the cerebral arteries that allows them to relax in the presence of the stimulus that earlier caused contraction.     

Regional disparity in the vascular response to subarachnoid hemorrhage--relationship between alteration of the concentration of eicosanoids and electron microscopic findings

In an attempt to document the apparent regional disparity of the vascular response to subarachnoid hemorrhage (SAH), the authors measured the concentrations of eicosanoids in various arterial segments corresponding to alterations observed on electron microscopy, using cats with experimentally produced SAH. The level of thromboxane B2 was elevated in both the arterial walls and cerebral cortices, particularly in the latter, on day 7 after SAH production. The 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) levels in the SAH group were decreased in the basilar and pial arteries after the production of SAH. The mean concentration of 6-keto-PGF1 alpha in the cerebral cortices showed only slight, erratic changes. Ultrastructural observations revealed that the vessels of smaller diameter, such as the pial vessels, underwent more marked spastic changes than did those of larger diameter. These results suggest that the ischemic events following SAH may have been induced by vasospasm and increased coagulability caused by changes in the concentrations of arachidonic acid metabolites in arteries of relatively small diameter.     

Chronic vasopeptidase inhibition restores endothelin-converting enzyme activity and normalizes endothelin levels in salt-induced hypertension.

BACKGROUND: Vasopeptidase inhibition (VPI) represents a new therapeutic principle including both inhibition of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP). The present study investigated the effect of the vasopeptidase inhibitor omapatrilat on endothelin-1 (ET-1)-mediated vascular function in salt-induced hypertension. METHODS: Dahl salt-sensitive rats (n=6/group) on standard or salt-enriched (4% NaCl) chow were treated for 8 weeks with either omapatrilat (36+/-4 mg/kg/day), captopril (94+/-2 mg/kg/day) or placebo. Aortic and renal artery segments were isolated and suspended in organ chambers for isometric tension recording. Functional endothelin-converting enzyme (ECE) activity was assessed in native segments and after preincubation with omapatrilat. Furthermore, vascular ECE protein levels as well as plasma and tissue ET-1 levels were determined. RESULTS: The increase in systolic blood pressure of salt-fed rats was prevented by omapatrilat and captopril to a comparable degree. In salt-induced hypertension, functional ECE activity (calculated as the ratio of the contraction to big ET-1 divided by the contraction to ET-1) in renal arteries (0.46+/-0.05) and in aorta (0.68+/-0.05) was reduced as compared with control animals (0.9+/-0.05 and 0.99+/-0.04, respectively; P<0.05). While omapatrilat in vitro blunted the response to big endothelin-1 (big ET-1) and diminished ECE activity further (P<0.01 vs native segments), chronic treatment with omapatrilat in vivo restored contractions to ET-1 (120+/-6%) and big ET-1 (98+/-9%) in renal arteries, and therefore normalized renovascular ECE activity. In addition, omapatrilat normalized plasma ET-1 concentrations (12.9+/-1.2 vs 16.6+/-1.4 pg/ml on high salt diet; P<0.05) and renovascular ECE protein levels. CONCLUSIONS: In salt-induced hypertension, vasopeptidase inhibition restores alterations in the endothelin system, such as renovascular ECE activity and responsiveness to ET-1 and big ET-1 with chronic but not acute in vitro application. Thus, the beneficial effects of vasopeptidase inhibition may reflect a resetting of cardiovascular control systems and therefore may be particularly suited to treat hypertension and heart failure.     

Reversal of cerebral vasospasm by sphenopalatine ganglion stimulation in a dog model of subarachnoid hemorrhage

BACKGROUND: Sphenopalatine ganglion stimulation dilates the ipsilateral arteries of the normal dog anterior circle of Willis. This experiment tested whether similar stimulation would reverse cerebral vasospasm. METHODS: Six dogs underwent baseline angiography followed by creation of subarachnoid hemorrhage (SAH) by injection of autologous blood into the cisterna magna. Two days later, subarachnoid blood injection was repeated. Seven days later, angiography was repeated and the left sphenopalatine ganglion was exposed microsurgically. Angiography was repeated 15 minutes after exposure of the ganglion. The ganglion was then stimulated electrically 3 times and angiography repeated during, and 15 and 30 minutes after stimulation. The protocol was repeated again. Adequacy of stimulation was confirmed by the presence of immediate ipsilateral nasal mucus production. RESULTS: Subarachnoid hemorrhage was associated with significant vasospasm of both middle cerebral arteries (11% +/- 4% and 18% +/- 7%, P < .05, paired t tests). Exposure of the ganglion and sham stimulation produced no substantial changes in arterial diameters compared with the diameter before stimulation and after ganglion exposure (n = 2-6 per measurement, paired t tests). Ganglion stimulation produced significant dilatation of the ipsilateral extracranial and intracranial internal carotid, middle cerebral, and anterior cerebral arteries compared with the contralateral arteries (13% +/- 6% to 32% +/- 14%, P < .05, paired t tests). CONCLUSIONS: The mild to moderate vasospasm that results from SAH in dogs was reversed by sphenopalatine ganglion stimulation. Since this method carries a potential for human application, additional studies are warranted to determine the effects on more severe vasospasm.     

The effect of timing of intrathecal fibrinolytic therapy on cerebral vasospasm in a primate model of subarachnoid hemorrhage

The effect of intrathecal tissue plasminogen activator administered at times from 0 to 72 hours after subarachnoid hemorrhage on the development of cerebral vasospasm in primates was examined. Thirty monkeys were randomly assigned into one of five equal groups: a control group that underwent subarachnoid hemorrhage alone, and 0-, 24-, 48-, and 72-hour treatment groups that received 0.75 mg of tissue plasminogen activator at those times after baseline cerebral angiography and subarachnoid hemorrhage on the right side. Seven days later angiography was repeated and the animals were killed. One animal in the 72-hour group developed a delayed ischemic deficit on Day 7 after subarachnoid hemorrhage. In the control and 72-hour groups significant vasospasm occurred in most of the major, right cerebral arteries (P less than 0.05), but no significant vasospasm developed in the 0-, 24-, and 48-hour groups. Although a large subarachnoid clot remained in the control animals, most clot had been dissolved in all treatment groups. Lysing of subarachnoid hematoma with intrathecal tissue plasminogen activator within 72 hours of subarachnoid hemorrhage is effective in preventing vasospasm in primates.     

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.     

Morphologic changes in cerebral arteries after subarachnoid hemorrhage

The premise of this article is that morphologic changes observed in cerebral arteries after subarachnoid hemorrhage play an important role in the pathogenesis of associated ischemic deficits observed in this disorder. Secondly, the arteriopathic response of cerebral arteries to subarachnoid blood is similar in many respects to that observed in systemic vessels under various pathologic conditions, and common pathogenic mechanisms may exist. The data supporting these premises may be summarized as follows: 1. Morphologic changes in human and animal cerebral arteries after subarachnoid hemorrhage are temporally associated with angiographic and clinically significant vasospasm. 2. Profound morphologic changes in cerebral arteries after subarachnoid hemorrhage do not contribute to structural narrowing of the lumen through increases in vessel wall mass. Nevertheless, structural changes may act in concert with contractile mechanisms to alter normal physiologic responses and maintain a narrowed lumen. 3. The agent responsible for arterial narrowing and morphologic changes in cerebral arteries after subarachnoid hemorrhage is contained in the erythrocyte component of whole blood and is most likely hemoglobin. 4. The volume and duration of exposure of subarachnoid blood to the artery appears to be significant in the development of the angiopathic response. 5. Ultrastructural abnormalities in systemic vessels associated with hypertension, atherogenesis, and endothelial damage are similar in many respects to those seen after subarachnoid hemorrhage.