Alleviation of brain edema by L-arginine following experimental subarachnoid hemorrhage in a rat model

Decreased levels of nitric oxide play a role in the development of cerebral ischemia secondary to subarachnoid hemorrhage (SAH). The protective effect of L-arginine on brain edema following SAH was investigated in this study. Rats were divided randomly into a sham-operated, a SAH+saline group and a SAH+L-arginine group. At different time points, brain water content was determined using the wet and dry weight compared method. Brain sodium content, potassium content and calcium content were detected using an atomic absorption spectral photometer. Somatosensory evoked potentials (SEP) were also detected. It was found that rat SAH models were successfully replicated. In the SAH+saline group, brain water and sodium content were significantly higher at 6 h and 24 h than those in the sham-operated group, while brain potassium content was statistically lower than that in the sham-operated group. Brain calcium content increased from 1 h to 24 h after induction of SAH. SEP latency progressively delayed. In the SAH+L-arginine group, increases in brain water content, sodium content and calcium content, as well as decreases in brain potassium content, were not as obvious as in the SAH+saline group. L-arginine partly prevented a delay in SEP latency. In conclusion, L-arginine, a substrate of nitric oxide synthesis, may relieve brain edema in rats with experimental SAH.     

Effects of blockade of cerebral lymphatic drainage on regional cerebral blood flow and brain edema after subarachnoid hemorrhage

The study was designed to observe the influence of blockade of cerebral lymphatic drainage on the regional cerebral blood flow (rCBF) and brain edema after experimental subarachnoid hemorrhage (SAH). Wistar rats were divided into non-SAH, SAH, and SAH plus cervical lymphatic blockade (SAH + CLB) groups. Autologous arterial hemolysate was injected into rat's cisterna magna to induce SAH. The rCBF was recorded continuously by a laser Doppler flowmeter. Intracranial pressure (ICP) was also monitored. After 24 hours and 72 hours of SAH, the rats were sacrificed and the brain was harvested for water content detection. It was found that there was no obvious change of rCBF and brain water content during the experiment in non-SAH group. An immediate and persistent drop in rCBF was found in SAH group. The drop in rCBF was more obvious in SAH + CLB group. CLB also worsened the SAH-induced increase in ICP. The brain water content 24 hours and 72 hours after induction of SAH in SAH group increased significantly. CLB led to a further increase of brain water content. In conclusion, blockade of cerebral lymphatic drainage pathway deteriorates the secondary cerebral ischemia and brain edema after SAH.     

尼莫地平对脑出血后缺血性脑损害保护作用的研究

目的探讨脑出血后继发性缺血性脑损害机制以及尼莫地平对脑出血后继发性缺血性脑损害的保护作用。方法60例脑出血患者随机分为尼莫地平组(30例)与常规治疗组(30例),在治疗前后用单光子发射型计算机断层显像(SPECT)观察原发灶缺血体积,血肿周围及脑部其他区域的局部脑血流量(rCBF)变化。结果尼莫地平组和常规治疗组治疗后原发灶缺血的体积明显缩小,原发灶缺血体积减少值尼莫地平组明显高于常规治疗组(P<0.01)。治疗后原发灶及远隔部位缺血灶rCBF增加值尼莫地平组明显高于常规治疗组(P<0.01)。结论脑出血后血肿周围及远隔区域可出现广泛的rCBF下降,血肿周围可能存在缺血半暗带。尼莫地平治疗脑出血有确切疗效,可改善局部脑缺血。     

大鼠脑缺血后肿瘤坏死因子样弱凋亡诱导物对脑水肿的影响

目的探讨肿瘤坏死因子样弱凋亡诱导物(tumor necrosis factor-like weak jnducer of apoptosis,TWEAK)在大鼠脑缺血后对脑水肿的影响。方法 Wistar大鼠36只,随机分为正常对照组、假手术组及脑缺血6 h组、脑缺血12 h组、脑缺血1天组和脑缺血2天组,每组6只。线栓方法制成大鼠脑缺血再灌注模型,测定各组脑含水量及伊文思蓝(EB)含量,免疫组织化学法检测TWEAK的表达。结果脑缺血6 h组大鼠脑含水量及EB含量显著增加,脑缺血2天组达高峰,分别为(81.21±0.27)%,(10.36±1.84)μg/g,与正常对照组和假手术组比较,有统计学差异(P<0.01)。脑缺血6 h组大鼠TWEAK的表达明显增加.脑缺血2天组进一步增加为(56.8±1.5)个/mm~2,与正常对照组和假手术组比较,有统计学差异(P<0.01)。结论 TWEAK很可能参与大鼠脑缺血后血脑屏障的破坏,并在脑水肿形成中起重要作用。     

Effects of blockade of cerebral lymphatic drainage on cerebral ischemia after middle cerebral artery occlusion in rats

This experiment aimed to investigate the effects of blockade of cerebral lymphatic drainage on cerebral ischemic damage. Seventy six Wistar rats were divided randomly into middle cerebral artery occlusion (MCAO) group and MCAO plus cerebral lymphatic blockade (MCAO+CLB) group for the experiment. The contents of water and electrolytes, the activity of superoxide dismutase (SOD) and the content of malondialdehyde (MDA) in the ischemic brain tissue were detected at 24, 48 and 72 hours after the operation. The morphologic examination was also performed. In MCAO group, contents of water, sodium and calcium in the ischemic brain tissue increased significantly at any time after the operation. The SOD activity decreased while the MDA content increased markedly. The morphologic findings showed severe damage of ischemic brain tissue and neurons. In MCAO+CLB group, the above parameters were altered more obviously. The present observation suggests that blockade of cerebral lymphatic drainage may deteriorate ischemic brain damage after MCAO.     

Effects of extract of Ginkgo biloba on spasms of the basilar artery and cerebral microcirculatory perfusion in rats with subarachnoid hemorrhage

This study was aimed at investigating the effects of extract of Ginkgo biloba (EGb) on cerebral vasospasm and microcirculatory perfusion after subarachnoid hemorrhage (SAH). An endovascular piercing method was used to induce Wistar rat SAH models, and animals were divided into sham-operated, vehicle controls, and EGb-treated groups. EGb was injected intraperitoneally 30 minutes before operation and was repeated every 6 hours, with a single dose of 15 mg/kg bw. Diameters of basilar arteries before and after operation were measured. Microcirculatory blood perfusion of parietal lobe cortex was detected using a laser Doppler flow-meter probe within 24 hours. Endothelin-1 levels in both plasma and brain tissue were detected at different time points. The results showed that SAH caused an immediate drop in microcirculatory blood flow in vehicle controls, which persisted for 24 hours. Endothelin-1 levels in both plasma and brain tissue increased after SAH. EGb partly reversed spasms of the basilar artery and antagonized a drop in microcirculatory blood flow. EGb also prevented an increase in endothelin-1 both in plasma and in brain tissue. In conclusion, EGb, by antagonizing the overproduction of endo- thelin-1, partly reverses cerebral vasospasm and improves microcirculation, and thus relieves secondary ischemic brain injury after experimental SAH.     

Zinc protoporphyrin aggravates cerebral ischemic injury following experimental subarachnoid hemorrhage

This study was aimed to evaluate the influence of an antagonist of heme oxygenase, zinc protoporphyrin IX (ZnPPIX), on the production of endogenous carbon monoxide (CO) and the secondary cerebral injury after subarachnoid hemorrhage (SAH). Wistar rats were divided into non-SAH, SAH, and ZnPPIX groups. Autologus arterial hemolysate was injected into rat cisterna magna to induce SAH. CO and cyclic guanosine monophosphate (cGMP) levels in the brain, and lactate dehydrogenase (LDH) activity in serum were determined 24 hours and 72 hours after cisternal injection. It was found that 24 hours and 72 hours after SAH, the CO contents in SAH group were increased by 20.76% and 37.36%, respectively. CO content in ZnPPIX group was statistically lower than that in SAH group. No obvious change of cGMP content in SAH group was found. However, cGMP content in ZnPPIX group was lower than that in SAH group. Serum LDH activity increased significantly after induction of SAH. LDH activity in ZnPPIX group increased to a greater extent. It was concluded that ZnPPIX aggravates the cerebral injury secondary to experimental SAH by inhibiting the production of endogenous CO. The activation of HO/CO pathway is an intrinsic protective mechanism against cerebral ischemic injury after SAH.     

L-arginine improves cerebral blood perfusion and vasomotion of microvessels following subarachnoid hemorrhage in rats

The purpose of this study is to investigate the effect of L-arginine (L-Arg) on cerebral blood perfusion and vasomotion (perfusion motion) in microvessels following subarachnoid hemorrhage (SAH). Rat noncraniotomy SAH models were used and animals were divided into sham-operated, saline-treated, and L-Arg-treated groups. L-Arg was injected intraperitoneally 30 minutes before the operation and repeated every 6 hours, with a single dose of 0.5 g/kg bw. Dynamic changes in regional cerebral blood flow (CBF) and vasomotion within 24 hours were measured using a laser Doppler flow-meter probe. Serum nitric oxide (nitrite/nitrate) and plasma endothelin-1 levels were also measured at different time points within 24 hours. Morphologic changes in neurons in the hippocampus CA1 region were examined. SAH gave rise to an immediate and persistent decrease in CBF in saline-treated rats. Abnormal vasomotions with decreased frequency and amplitude were observed. Serum nitric oxide decreased, while plasma endothelin-1 increased significantly. Neurons in the hippocampus CA1 region were severely damaged. The above pathological alterations in the L-Arg-treated group were alleviated. It was concluded that L-Arg, which increases cerebral blood perfusion and improves vasomotions of microvessels by enhancing nitric oxide levels and decreasing endothelin-1 levels in blood, exerts a protective effect on secondary cerebral ischemic injury following experimental SAH.     

大鼠蛛网膜下腔出血后急性脑血管痉挛血及脑组织一氧化氮和内皮素含量的动态观察

目的 探讨一氧化氮（ＮＯ）、内皮素（ＥＴ）在蛛网膜下腔出血（ＳＡＨ）后急性脑出血痉挛（ＣＶＳ）中的作用。方法 对ＳＡＨ模型组和假手术组大脑检测术后２４ｈ内局部脑血流量（ｒＢＣＦ）、血浆及脑组织ＮＯ、ＥＴ含量的动态改变,并测量基底动脉（ＢＡ）管径,３ｄ后行海马组织病理检查。结果 ＳＡＨ后２４ｈ内ｒＣＢＦ迅速而持续降低,ＢＡ痉挛;３ｄ后海马ＣＡ１区神经元明显受损,血清ＮＯ明显减少,脑组织ＮＯ显著增多,     

R－型钙通道阻滞剂对大鼠蛛网膜下腔出血后脑动脉钙通道相关蛋白的影响

目的研究蛛网膜下腔出血（SAH）后脑动脉R-型钙通道的表达情况,并探讨R-型钙通道阻滞剂——SNX-482对脑动脉收缩相关蛋白的作用。方法20只雄性SD大鼠,随机分为假手术组、SAH组、SAH＋尼莫地平组、SAH＋SNX-482组,每组5只。采用大鼠鞍上池注射自体动脉血法制备SAH模型,其后第1、2日每天向假手术组和SAH组的脑池内注射25μl等渗盐水,向SAH＋尼莫地平组和SAH＋SNX-482组注射25μl尼莫地平或SNX-482。第3日取脑动脉标本,后经SDS-聚丙烯酰胺凝胶电泳和蛋白印迹半定量检测R-型钙通道蛋白和调宁蛋白（calponin）的表达水平,经尿素甘油-聚丙烯酰胺凝胶电泳和蛋白印迹检测肌球蛋白轻链2（MLC2）磷酸化百分比。结果①假手术组、SAH组、SAH＋尼莫地平组和SAH＋SNX-482组R-型钙通道蛋白相对量分别为0．38±0．08、0．86±0．07、0．66±0．11和0．72±0．09,假手术组的蛋白相对量均低于其他三组（P〈0．05）;②上述各组calponin相对量分别为2．32±0．14、0．54±0．17、0．75±0．19和1．42±0．15,各组间差异均具有统计学意义（P〈0．05）;③上述各组MLC2磷酸化百分比依次为12．2±2．8、41．0±3．2、36．1±2．8和25．3±1．9,除SAH和SAH＋尼莫地平两组外,其余各组间差异均具有统计学意义（P〈0．05）。结论R-型钙通道阻滞剂可抑制SAH大鼠脑动脉的calponin降解和MLC2磷酸化的程度,其作用强于L-型钙通道阻滞剂尼莫地平。     

大鼠脑缺血再灌注后超早期-过性过度灌注现象的病理生理学机制研究

目的 探讨脑缺血再灌注后自发性一过性过度灌注现象的病理生理学机制.方法 52只SD大鼠随机分为假手术组(A组)、缺血2 h组(B组)和缺血6 h组(C组),B组按再灌注时间分为0 h、0.5 h、1 h、2 h、4 h、6 h、24 h组,C组按再灌注时间分为0 h、0.5 h、1 h、2 h、24 h组,每组4只.各组动物在缺血后再灌注不同时间点行多层螺旋CT灌注成像(CT perfusion imaging,CTPI),扫描完成后立即处死大鼠行光学和电子显微镜检查.结果 A组假手术区脑血流灌注参数相对值及光学和电子显微镜结果与对侧无显著差异.随着再灌注时间的延长,B组缺血核心区相对脑血流量(relativecerebral blood flow,rCBF)和相对脑血容量(relative cerebral blood volume,rCBV)逐渐上升,相对平均通过时间(relative mean transit time,rMTT)和相对达峰时间(relative time to peak,rTTP)逐渐下降,再灌注6 h后与A组相比无显著差异.光学和电子显微镜显示,B组缺血核心区神经元密度降低,部分细胞体积增大呈空泡变,部分神经元胞体和胞核浓缩.C组随着再灌注时间的延长,缺血核心区rCBF仍维持在较低水平.再灌注0.5 h,B组和C组在缺血核心区均出现一过性rCBF和rCBV增高现象,光学和电子显微镜显示此时缺血核心区出现大量凋亡和坏死细胞以及炎症细胞浸润.再灌注6 h,B组缺血核心区电镜下可见血管密度增高,微血管怒张.结论 CIPI在大鼠大脑中动脉闭塞和再灌注过程中的动态变化与病理学损伤机制具有一定相关性,大鼠脑缺血再灌注后超早期自发性一过性过度灌注现象与灌注损伤后的一过性炎性充血有关.     

尼莫地平对兔蛛网膜下腔出血后症状性脑血管痉挛的影响

目的探讨尼莫地平对兔蛛网膜下腔出血（SAH）后症状性脑血管痉挛的影响。方法建立症状性脑血管痉挛动物模型，SAH＋尼莫地平组静脉内应用尼莫地平。观察对比神经功能缺损症状改善、血液流变学及电镜结果。结果SAH＋尼莫地平组随着尼莫地平的应用,神经功能缺损症状逐渐好转、血液流变学得到改善、透射电镜见基底动脉病理改变较SAH组减轻。结论SAH后早期应用尼莫地平对症状性脑血管痉挛具有明显的改善作用。     

联合应用尼莫地平和胞磷胆碱对大鼠局灶性脑缺血的神经保护作用

目的探讨联合应用尼莫地平、胞磷胆碱对局灶性脑缺血-再灌注大鼠的脑保护作用。方法Sprague-Dawley雄性大鼠48只,随机分为缺血对照组,尼莫地平组,胞磷胆碱组及联合用药组,每组12只。线栓法制作大脑中动脉栓塞90min,同侧颈总动脉结扎60min模型。尼莫地平经颈内动脉给药（40μg/kg）;胞磷胆碱经腹腔注射给药（250mg/kg,1次/d,连用3d）。再灌注后24h行神经功能缺损评分;再灌注后72h测量脑组织梗死体积,采用流式细胞仪检测大鼠前脑皮质细胞凋亡率。结果对照组、尼莫地平组、胞磷胆碱组及联合用药组神经功能缺损评分分别为2.6±0.8、1.5±1.2、1.2±0.8和0.7±0.6;脑梗死体积分别为（186±25）、（122±22）、（119±21）和（81±27）mm^3;细胞凋亡率分别为（30.6±1.9）、（8.8±2.0）、（4.6±2.4）、（2.2±1.7）%。所有观察指标,用药组与对照组比较,差异均有统计学意义（P〈0.05）;尼莫地平组与胞磷胆碱组相比,无统计学意义（P〉0.05）;联合用药组与尼莫地平组或胞磷胆碱组比较,差异有统计学意义（P〈0.05）。HE染色显示,所有用药组神经细胞缺血性损伤较对照组明显减轻。结论脑缺血-再灌注后,尼莫地平和胞磷胆碱早期使用均有效,两药联合使用疗效优于单独用药。     

Effect of calcium antagonists on the cerebral circulation

Current research suggests that cerebral ischemia induces a cascade of pathophysiologic reactions. A massive influx of calcium into the neuron constitutes the "final common pathway," resulting in catabolism and cell necrosis due to calcium overload. Treatment with calcium antagonists may offer a means of arresting and possibly preventing the destruction of cerebral tissue in patients with stroke. One such drug, nimodipine, selectively inhibits spasm of isolated cerebral arteries induced by either depolarization or receptor stimulation. In vivo experiments have shown that nimodipine prevents the postischemic impairment of cerebral blood flow that may be a major contributor to neuronal damage. After encouraging although not conclusive results of a single-blind pilot study, a double-blind, placebo-controlled, multicenter clinical investigation of nimodipine was undertaken. Some benefit was strongly suggested in patients with acute ischemic stroke who were treated with 120 mg of nimodipine, begun within 24 hours after the onset of the event, combined with "standard" treatment (i.e., hemodilution using low molecular dextran). Calcium antagonists such as nimodipine may be useful in the treatment of stroke due to acute cerebral ischemia.     

丹星通络汤治疗大鼠脑缺血再灌注Bax蛋白表达的影响

目的 观察丹星通络汤对大鼠脑缺血再灌注损伤海马区细胞凋亡调控基因Bax蛋白表达的影响,探讨丹星通络汤预防与治疗大鼠脑缺血再灌注损伤的作用.方法 SD大鼠40只,随机分成假手术组、模型组、尼莫地平组、丹星通络汤小剂量组、丹星通络汤大剂量组,每组8只.采用线栓法制备大鼠大脑中动脉闭塞(MCAO)再灌注模型.HE染色检测大鼠脑组织海马区的病理学变化,免疫组织化学法和医学图像分析法检测大鼠脑组织海马区Bax蛋白的平均光密度(OD)值.结果 与模型组比较,丹星通络汤大、小剂量组大鼠脑组织海马区Bax蛋白的OD值明显减低(P＜0.05),并且丹星通络汤大剂量组与尼莫地平组相比有统计学意义(P＜0.05).结论 丹星通络汤可能通过下调Bax蛋白的表达,从而抑制脑组织的凋亡机制发挥对脑组织的保护作用.     

Effects of phenytoin on regional cerebral blood flow, electroencephalogram, and electrolyte contents in cerebral blood and cerebral cortex following total cerebral ischemia in dogs

To study the protective effect of phenytoin on postischemic brain damage, total cerebral ischemia was produced for 8-12 min (aortic occlusion balloon catheter method) in 36 adult mongrel dogs. The regional cerebral blood flow (rCBF), sodium:potassium ratio in the cerebral cortex, electroencephalogram (EEG), and plasma electrolytes in the superior sagittal sinus blood were examined before ischemia and during the acute stage up to 120 min after recirculation in the control and phenytoin-treated groups. Measurement of rCBF (microsphere method) indicated easing of postischemic hypoperfusion of the cerebral cortex. The time from total cerebral ischemia to EEG electrical silence was significantly prolonged, and recovery of the electrical activity after recirculation was hastened. The increase in plasma potassium concentration in the superior sagittal sinus tended to be suppressed immediately after recirculation, and the sodium:potassium ratio in the cerebral cortex was lowered. Phenytoin increased the rCBF in the cerebral cortex, hastened the recovery of electrical activity, and stabilized the water and electrolyte balance in the cerebral cortex, suggesting some protecting effect on total cerebral ischemia.     

脑脉通对老龄大鼠脑缺血再灌注神经细胞凋亡及相关基因表达的影响

目的　从神经细胞凋亡方面研究脑脉通对老龄大鼠脑缺血再灌注脑损伤的保护作用。方法　采用线栓法建立老龄大鼠急性局灶性脑缺血再灌注损伤模型 ,观察脑脉通对老龄大鼠脑缺血 3h及再灌注 3h、6h、1 2h、2 4h、72h各组神经细胞凋亡及相关的Bcl 2、Bax基因表达影响 ,并与尼莫地平对照。结果　脑缺血再灌注脑组织细胞损伤明显 ,细胞凋亡显著 ,Bax表达增强。脑脉通和尼莫地平能够明显改善脑组织损伤 ,降低神经细胞凋亡。在脑缺血再灌注过程中 ,尼莫地平可使缺血 3h及再灌注 3h的Bcl 2表达增强 ,降低缺血再灌注过程中Bax表达。脑脉通可明显促进Bcl 2表达和降低Bax表达。脑脉通促进Bcl 2表达的作用明显强于尼莫地平。结论　脑脉通可以通过调控细胞凋亡相关基因Bcl 2 /Bax基因表达 ,对局灶性脑缺血 /再灌后神经元起保护作用     

Regional cerebral blood flow in patients with internal carotid artery stenosis: Effects of nifedipine and nimodipine

Regional cerebral blood flow (rCBF) in 87 patients with CBF decreased due to unilateral stenosis of internal carotid artery was studied by using the¹³³xenon infusion technique and a 30-detector setup. On the side of stenosis a decrease in the mean hemispheric blood flow (rCBFh) with an elevated deviation of rCBF from rCBFh was observed. Administration of a single oral dose of either nifedipine or nimodipine induced various changes in rCBF. A classification of their effects with due regard for changes in both the mean value of the hemispheric blood flow and the flow distribution is described. The decrease in both the interhemispheric difference of rCBFh and the deviation of rCBF from the hemispheric mean flow accompanying the increase of the total brain blood flow was considered as being the most beneficial drug effect. This positive reaction was found more frequently when nimodipine was used. In some patients nifedipine, and in fewer, nimodipine, induced nonbeneficial changes in rCBF with elevation of the interhemispheric difference and an increase in the number of ischemic and hyperemic regions on the side of stenosis. The types of drug effects after administration of a single dose were similar to those after two weeks of monotherapy. It is supported that this approach allows assessment of cerebral hemodynamics and drug effectiveness in cerebrovascular disorders.     

Nimodipine and Its Use in Cerebrovascular Disease: Evidence from Recent Preclinical and Controlled Clinical Studies

Nimodipine is a 1,4-dihydropyridine-derivative Ca²⁺-channel blocker developed approximately 30 years ago. It is highly lipophilic, crosses the blood-brain barrier, and reaches brain and cerebrospinal fluid. Early treatment with nimodipine reduces the severity of neurological deficits resulting from vasospasm in subarachnoid haemorrhage (SAH) patients. In SAH, nimodipine reduced spasm-related deficits of all severities, but no spasm-unrelated deficits. This paper has reviewed preclinical studies on the influence of nimodipine in various animal models of cerebral ischemia, with particular attention toward investigations published in the last 10 years. These studies further support the main indication of nimodipine, by clarifying some mechanisms of the anti-ischemic activity of the compound. Papers reporting a possible role of nimodipine in epileptogenesis were also examined. Clinical studies on nimodipine were grouped into subarachnoid hemorrhage, acute ischemic stroke, cerebral ischemia without stroke, dementia disorders, and migraine. Clinical investigations have shown that the drug improves neurological outcome by reducing the incidence and severity of ischemic deficits in patients with SAH from ruptured intracranial berry aneurysms regardless of their post-ictus neurological condition. No relevant effects of treatment with nimodipine were reported for acute ischemic stroke, cerebral ischemia without stroke, and migraine, except than for cluster headache. The less pronounced cardiovascular effects of nimodipine compared to other dihydropyridine-type Ca²⁺-channel blockers probably accounts for its use out of label for treating patients affected by chronic cerebral ischemia and vascular cognitive impairment. However, the blood pressure-lowering effects of nimodipine should not be minimized, as clinical studies have documented lowering blood pressure in small groups of patients, including cases of withdrawn due to pronounced hypotension induced by nimodipine administration. In the area of vascular cognitive impairment, short-term benefits of nimodipine do not justify its use as a long-term anti-dementia drug, and benefits obtained in elderly patients affected by subcortical vascular dementia require to be confirmed by other groups and in larger scale trials. In conclusion, nimodipine is a safe drug with an important place in pharmacotherapy and with the main documentation for reduction in the severity of neurological deficits resulting from vasospam in SAH patients.     

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

Summary 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 96h 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 F₂, 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 48h after SAH, while most of the responses to the other agonists began to decrease in the clot-removal groups later than 72h 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 48h after the SAH. Clot removal may thus be recommended within 48h after SAH to ameliorate the severity of cerebral vasospasm following SAH.