低频治疗性超声波联合微泡造影剂辅助溶栓的实验研究

目的观察体外低频治疗性超声波(ETUS)与超声微泡造影剂(MB)对尿激酶溶栓效果的影响,寻求最佳溶栓方案并探讨其作用机制,为临床应用低频ETUS联合微泡治疗急性缺血性脑卒中提供理论依据。方法抽取健康志愿者静脉血孵化老龄血栓。按照配伍组设计原则分成对照组(NS)、尿激酶组(UK)、超声组(ETUS)、超声联合尿激酶组(ETUS UK)、超声联合微泡组(ETUS MB)、超声联合微泡与尿激酶组(ETUS UK MB)。按实验操作方法进行溶栓20 min,对各组溶栓效果进行比较。结果各实验组的血栓溶解百分率分别为:NS组(7.0750±3.0491)%;UK组(15.6610±4.6009)%;ETUS组(8.0000±2.7907)%;ETUS UK组(18.5420±4.2393)%;ETUS MB组(29.0430±7.0044)%(与UK组比较P<0.01)ETUS UK MB组(50.0810±6.9949)%(与各组比较P<0.01)。结论低频ETUS联合微泡能够明显提高尿激酶对体外血栓溶解率。     

依达拉奉对大鼠脑梗死溶栓治疗后MMP-9表达的影响

目的研究依达拉奉对大鼠脑梗死溶栓治疗后脑组织中MMP-9表达及血脑屏障的影响,探讨依达拉奉对脑梗死溶栓治疗后再灌注损伤的保护机制。方法采用SD大鼠自体血栓栓塞法制备大脑中动脉闭塞模型,并将SD大鼠随机分为假手术组、尿激酶溶栓治疗组(UK)、尿激酶+依达拉奉治疗组(UK+ED),12h后分别以免疫组织化学法和比色法对SD大鼠脑组织中MMP-9表达水平和伊文思蓝含量进行测定。结果与尿激酶溶栓治疗组相比,尿激酶+依达拉奉组SD大鼠缺血侧脑组织MMP-9表达水平和EB含量均显著降低,差异具有统计学意义(P值均<0.01)。结论依达拉奉可能通过下调MMP-9表达,减轻血脑屏障的破坏,减轻溶栓后脑缺血再灌注损伤。     

超声增强溶栓作用的体外实验研究

目的评估超声的溶栓作用和能否增强尿激酶的溶栓作用。方法采用体外实验方法,先制备血栓,置于37℃流动的缓冲液中,超声照射距离为4cm,脉冲式照射,时间为60、90、120、180min,观察同一频率(800kHz)、不同声强(0.2~0.8W/cm2)的超声和超声加尿激酶(0.17U/ml,0.34U/ml)对血栓失重的影响。所测的数据经统计学处理。结果从血栓失重的结果来看,与对照组相比,0.2W/cm2的超声,180min时的血栓失重,有统计学意义(P<0.05)。随着声强增大,有统计学意义的溶栓时间明显缩短,0.4W/cm2时为90min,而0.6W/cm2和0.8W/cm2时,60min即出现非常显著的差异(P<0.001)。超声(800kHz、0.6W/cm2)加尿激酶的溶栓结果,60min时即有非常显著溶栓作用(P<0.001),血栓重量,从起始的(508±5.51)mg减少至180min的(347.66±3.66)mg,减少了(161±1.85)mg,而单用尿激酶组只减少99.5±5.02mg。两组各个时段所测得的血栓失重相比均有明显差异(P<0.001)。结论本组所用的超声对血栓有显著的溶解作用,超声加尿激酶则有增强溶栓作用。     

大鼠溶栓模型的建立及超早期溶栓治疗的有效性

目的 建立大鼠血栓栓塞模型及探讨超早期尿激酶溶栓治疗的有效性。方法 用自体血体外制备栓子,经颈外动脉推入,栓塞大脑中动脉,半小时或4小时后分别予以尿激酶或生理盐水治疗。6小时后检查血栓的位置,测定梗死灶大小,及进行组织病理学检查。结果 生理盐水治疗组6小时后大脑中动脉起始部均见栓子存在,尿激酶治疗组栓子完全溶解;生理盐水治疗组和4小时溶栓治疗组梗死灶大小无显著性差异(P<0.05),而半小时溶栓治疗组梗死灶明显较前两组小(P<0.05),细胞坏死程度减轻。结论 本模型可复制性强,溶栓治疗后血管再通率高,梗死灶大小恒定,是进行溶栓研究的理想模型。超早期溶栓梗死灶明显减小。     

经颅超声溶栓治疗超早期急性脑梗死的临床研究

目的评价经颅超声溶栓治疗超早期急性脑梗死的临床疗效。方法急性脑梗死患者80例,均为发病6 h内就诊者。同意溶栓治疗的患者66例随机分为3组:尿激酶(UK)溶栓组、经颅超声溶栓组、经颅超声加尿激酶溶栓组,每组22例。不同意溶栓治疗的患者14例作为对照组,只接受对症治疗。尿激酶100万U溶于生理盐水100 ml静滴,1/2h内滴完。应用经颅超声溶栓治疗仪(频率:800 kHz,0.75W/cm2,脉冲超声)治疗,1次/d,20 min/次,共10d。对各组治疗前后的神经功能缺损、日常生活能力及凝血功能进行分析比较。结果治疗后3个月,按欧洲卒中评分标准评分,经颅超声加尿激酶治疗组得分最高(95.33±3.37),对照组最低(79.17±8.73),即经颅超声加尿激酶治疗对恢复神经功能缺损的效果最显著;按Barthel指数评分,轻度残疾或无残疾的比例最高(85.71%),对照组最低(41.67%)。对凝血功能无影响,未见不良反应。结论经颅超声有溶栓作用,并可增强尿激酶的溶栓效果,能促使神经功能恢复。因此,经颅超声溶栓治疗急性脑梗死是一种安全、有效、操作简单的治疗方法。     

超声评价法优化三氯化铁诱导大鼠颈总动脉血栓模型的研究

目的探讨采用连续超声评价法优化不同三氯化铁浓度梯度和作用时间诱导大鼠颈总动脉血栓模型,为溶栓及取栓研究提供合适的在体血栓模型。方法选取20只(Sprague–Dawley)SD大鼠,每组5只,分别采用20%、30%、40%、50%四种三氯化铁浓度外敷大鼠单侧颈总动脉,使用14 L高频超声探头,分别在外敷10min、15 min、20 min三个时间点观察血管二维超声图像及彩色多普勒血流情况。选取血管闭塞最佳组大鼠,于干预120 min后观察血管自发再通率及静脉注射尿激酶后的血管再通率。实验结束后,取出干预血管甲醛固定,石蜡包埋,切片,进行HE染色病理分析。结果三氯化铁外敷大鼠颈总动脉20 min、50%浓度组血管闭塞率100%,40%、30%、20%浓度组外敷20 min血管闭塞率分别20%、0%、0%(P0.001)。外敷120 min后,50%浓度组组血管自发再通率0%、40%、30%、20%组血管自发再通率100%(P0.001),50%三氯化铁浓度造模组尾静脉注射尿激酶后血管部分再通率为40%。50%浓度组镜下病理显示血栓结构致密,尿激酶干预后管腔部分再通,血栓结构松散。结论采用50%三氯化铁浓度外敷大鼠颈总动脉20 min,可能是在体血栓模型形成的有效条件,该动物模型可能适合溶栓研究。     

兔颈内动脉栓塞后不同给药途径的溶栓效果及安全性

目的:评价尿激酶不同给药途径的溶栓效果及安全性。方法:将新鲜兔血栓注入新西兰白兔的一侧颈内动脉(1CA),15min后经不同的途径给予尿激酶(UK)治疗。结果:治疗开始后2h内动脉途径组(10000u·kg~(-1))血管再通率100%;静脉途径组(10000和20000u·kg~(-1))分别为33%和100%。动脉途径组平均再通时间(53.6±13.1)min,静脉途径组(20000u·kg~(-1))为(89.1±14.8)min。结论:动脉途径的溶栓效果及安全性优于静脉途径。     

急性大脑中动脉栓塞的动静脉联合溶栓治疗的实验研究

目的:评价动静脉联合溶栓治疗实验兔急性脑梗死的疗效。方法:采用兔自体血栓栓塞大脑中动脉制成急性脑梗死模型,随机分为动、静脉联合溶栓组(IA+IV组)、静脉溶栓组(IV组)及对照组,分别给予以动脉+静脉、静脉内注射尿激酶及静脉内注射生理盐水。采用DSA观察血管再通率、核磁共振弥散成像观察相对表观系数(rADC)、改良Bederson评分法观察神经功能缺损。结果:IA+IV组血管再通率为83.3%、rADC值(0.918±0.144)及神经功能缺损评分(0.80±0.84)均优于IV组和对照组。结论:动静脉联合溶栓治疗急性脑梗死优于静脉内溶栓治疗。     

尿激酶联合镁剂治疗大鼠急性脑梗死的实验研究

目的　观察尿激酶溶栓联合硫酸镁神经保护对大鼠急性脑梗死的疗效。方法　应用光化学诱导法建立大鼠大脑中动脉闭塞(MCAO)模型,分别于术后2 h、6 h和10 h 3 个时间点进行干预,每个时间点内再分为生理盐水对照组、尿激酶溶栓组、尿激酶加硫酸镁治疗组,术后24 h观察大鼠神经功能缺损评分及脑梗死体积的变化。结果　MCAO后2 h尿激酶溶栓组神经功能显著改善,梗死体积缩小(与生理盐水对照组相比,P<0.01),尿激酶加硫酸镁治疗组效果更好;MCAO后6 h、10 h尿激酶溶栓组与生理盐水对照组相比无显著性差异(P>0.05),而尿激酶加硫酸镁治疗组的神经功能缺损评分、脑梗死体积与生理盐水对照组及尿激酶溶栓组相比有显著差异(P<0.05或P<0.01)。结论　早期脑梗死特别是2 h内的超早期脑梗死应用尿激酶溶栓有效;加用镁剂进行神经保护可对尿激酶溶栓疗效产生协同作用,并可能扩大脑梗死溶栓治疗的时间窗。     

经颅多普勒超声监护下超声微泡剂对尿激酶溶栓治疗作用的影响

目的 评价经颅多普勒超声(TCD)监护下超声微泡剂辅助尿激酶溶栓治疗的有效性. 方法 将雄性新西兰大白兔32只按随机数字表法分为单用尿激酶组和尿激酶联合超声微泡剂组,每组各16只.采用兔颈外动脉插管注入自体血栓方法制备成大脑中动脉栓塞模型,并应用TCD监测血栓溶解过程.尿激酶联合超声微泡剂组静注尿激酶后立即静注六氟化硫超声微泡剂(声诺维).2组动物均在溶栓治疗后2h内持续TCD监测并记录溶栓治疗后不同时间点大脑中动脉血流动力学变化,并根据TCD频谱形态及血流速度判断血管再通情况. 结果 2组动物溶栓治疗前大脑中动脉的平均血流速度比较差异无统计学意义(P＞0.05).溶栓治疗后单用尿激酶组完全再通l例,部分再通4例,血管再通率为31.3％;尿激酶联合超声微泡剂组完全再通3例,部分再通6例,血管再通率为56.3％.2组动物病理检查均未见脑出血.单用尿激酶组梗死灶大小占梗死半球的百分率平均为13.9％,尿激酶联合超声微泡剂组梗死灶大小占梗死半球的百分率平均为9.1％,比较差异有统计学意义(P=0.025). 结论 TCD监测下应用超声微泡剂有助于增强尿激酶的溶栓治疗效果,初步证明TCD联合超声微泡剂可辅助尿激酶溶栓治疗脑梗死.     

Effect of low frequency ultrasound on combined rt-PA and eptifibatide thrombolysis in human clots

INTRODUCTION: Fibrinolytics such as recombinant tissue plasminogen activator (rt-PA) are used to treat thrombotic disease such as acute myocardial infarction (AMI) and ischemic stroke. Interest in increasing efficacy and reducing side effects has led to the study of adjuncts such as GP IIb-IIIa inhibitors and ultrasound (US) enhanced thrombolysis. Currently, GP IIb-IIIa inhibitor and fibrinolytic treatment are often used in AMI, and are under investigation for stroke treatment. However, little is known of the efficacy of combined GP IIb-IIIa inhibitor, fibrinolytic and ultrasound treatment. We measure the lytic efficacy of rt-PA, eptifibatide (Epf) and 120 kHz ultrasound treatment in an in-vitro human clot model. MATERIALS AND METHODS: Blood was drawn from 15 subjects after IRB approval. Clots were made in 20 microL pipettes, and placed in a water tank for microscopic visualization during lytic treatment. Clots were exposed to control, rt-PA (rt-PA), eptifibatide (Epf), or rt-PA+eptifibatide (rt-PA + Epf), with (+US) or without (-US) ultrasound for 30 minutes at 37 degrees C in human plasma. Clot lysis was measured over time, using a microscopic imaging technique. The fractional clot loss (FCL) and initial lytic rate (LR) were used to quantify lytic efficacy. RESULTS AND CONCLUSIONS: LR values for (- US) treated clots were 0.8+/-0.1(control), 1.8+/-0.3 (Epf), 1.5+/-0.2 (rt-PA), and 1.3+/-0.4 (rt-PA + Epf) (% clot width/minute) respectively. In comparison, the (+ US) group exhibited LR values of 1.6+/-0.2 (control), 4.3+/-0.4 (Epf), 6.3+/-0.4 (rt-PA), and 4.6+/-0.6 (rt-PA + Epf). For (- US) treated clots, FCL was 6.0+/-0.8 (control), 9.2+/-2.5 (Epf), 15.6+/-1.7 (rt-PA), and 28.0+/-2.2% (rt-PA + Epf) respectively. FCL for (+ US) clots was 13.5+/-2.4 (control), 20.7+/-6.4 (Epf), 44.4+/-3.6 (rt-PA) and 30.3+/-3.6% (rt-PA + Epf) respectively. Although the addition of eptifibatide enhances the in-vitro lytic efficacy of rt-PA in the absence of ultrasound, the efficacy of ultrasound and rt-PA is greater than that of combined ultrasound, rt-PA and eptifibatide exposure.     

尿激酶溶栓联合亚低温治疗对急性脑梗死患者血浆F1+2及D-D的影响

目的通过研究尿激酶溶栓联合亚低温治疗对血浆F1+2及D-D的影响,探讨其对急性脑梗死患者凝血、纤溶系统的作用机制。方法将29例急性脑梗死患者分为溶栓组及低温组,观察其在溶栓前和溶栓后不同时点的F1+2及D-D水平。结果尿激酶溶栓联合亚低温治疗能显著抑制F1+2及D-D。结论尿激酶溶栓联合亚低温治疗对急性脑梗死患者凝血和纤溶系统具有一定影响,可以显著降低患者血栓再形成的风险。     

Ultrasound affects distribution of plasminogen and tissue-type plasminogen activator in whole blood clots in vitro

Ultrasound of 2 MHz frequency and 1.2 W/cm(2) acoustic intensity was applied to examine the effect of sonication on recombinant tissue-type plasminogen activator (rt-PA)-induced thrombolysis as well as on the distribution of plasminogen and t-PA within whole blood clots in vitro. Thrombolysis was evaluated quantitatively by measuring clot weight reduction and the level of fibrin degradation product D-dimer (FDP-DD) in the supernatant. Weight reduction in the group of clots treated both with ultrasound and rt-PA was 35.2% +/-6.9% which is significantly higher (p<0.0001) than in the group of clots treated with rt-PA only (19.9% +/-4.3%). FDP-DD level in the supernatants of the group treated with ultrasound and rt-PA increased sevenfold compared to the group treated with rt-PA alone, (14895 +/-2513 ng/ml vs. 2364 +/-725 ng/ml). Localization of fibrinolytic components within the clots was accomplished by using gel-entrapping technique and immunohistochemistry. Spatial distributions of t-PA and plasminogen showed clearly that ultrasound promoted the penetration of rt-PA into thrombi significantly (p<0.0001), and broadened the zone of lysis from 8.9 +/-2.6 microm to 21.2 +/-7.2 microm. We speculate that ultrasound enhances thrombolysis by affecting the distribution of rt-PA within the clot.     

Dependence of blood clot lysis on the mode of transport of urokinase into the clot--a magnetic resonance imaging study in vitro

Magnetic resonance imaging was employed to study the dependence of clot lysing patterns on two different modes of transport of urokinase into whole blood clots. In one group of clots (nonperfused clots, n1 = 10), access of urokinase to the fibrin network was possible by diffusion only, whereas in the other group (perfused clots, n2 = 10) bulk flow of plasma containing urokinase was instituted through occlusive clots by a pressure difference of 3.7 kPa (37 cm H2O) across 3 cm long clots with a diameter of 4 mm. It was determined separately that this pressure difference resulted in a volume flow rate of 5.05 +/- 2.4 x 10(-2) ml/min through occlusive clots. Perfused clots diminished in size significantly in comparison to nonperfused ones already after 20 min (p less than 0.005). Linear regression analysis of two-dimensional clot sizes measured by MRI showed that the rate of lysis was more than 50-times faster in the perfused group in comparison to the nonperfused group. It was concluded that penetration of the thrombolytic agent into clots by perfusion is much more effective than by diffusion. Our results might have some implications for understanding the differences in lysis of arterial and venous thrombi.     

Therapeutic effect of diagnostic ultrasound on enzymatic thrombolysis. An in vitro study on blood of normal subjects and patients with coronary artery disease

If delivered at elevated intensity, ultrasound potentiates enzymatic clot dissolution; however, an elevated acoustic intensity damages vascular wall and favors reocclusion. This study's aim was to investigate whether exposure to high-frequency, low-intensity ultrasound - generated by a diagnostic scanner -enhances enzymatic thrombolysis, and if this effect differs in clots from blood of normal subjects and of patients with coronary artery disease (CAD). Venous blood samples were drawn from 10 healthy volunteers and from 10 CAD patients on chronic medical treatment, which also included aspirin. Each sample generated 2 radiolabelled clots, which were positioned in 2 in vitro models filled with human plasma recirculating at 37 degrees. One clot was exposed to acetyl salicylic acid (60 microg/ml), tissue plasminogen activator (3 microg/ml) and heparin (1 IU/ml), while the other was exposed to the same medications plus ultra-sound (2.5 MHz, mechanical index = 1.0) for 3 hours. Enzymatic thrombolysis was measured as solubilization of radiolabel. Normal subjects and patients did not significantly differ as to coagulation parameters, weight, volume and density of the clots, and fibrinolytic activity (p = 0.794). Ultrasound exposure did not influence thrombolysis in clots of normal subjects (p = 0.367), while it enhanced the dissolution of clots of CAD patients (p = 0.013). The enhancement was equal to 51% at 5 minutes, 32% at 15 minutes, 27% at 30 minutes, 20% at 1 hour and 19% at 3 hours (p < 0.05). Diagnostic ultrasound enhances enzymatic dissolution of clots generated from the blood of CAD patients, likely due to chronic treatment and in particular to aspirin.     

溶栓联合神经保护剂对大鼠脑梗死的保护作用

目的探讨高危儿早期干预降低脑性瘫痪发生率的效果。方法高危儿120例分为早期干预组(60例)和常规组(60例)。干预组除接受常规育儿指导外,还进行综合的康复训练。常规组仅接受常规的育儿指导。结果1岁时脑性瘫痪发生率干预组为3.33%(2/60),常规组为16.67%(10/60),2组比较差异有统计学意义(P<0.05)。结论高危儿早期干预可降低脑瘫的发生率。     

Effects of microbubbles on transcranial Doppler ultrasound-assisted intracranial urokinase thrombolysis

Introduction

To evaluate the efficacy of microbubbles in transcranial Doppler ultrasound (TCD)-assisted urokinase thrombolysis.

Materials and Methods

Male New Zealand white rabbits (N = 32) were randomly divided into 2 groups, a urokinase group and a combined urokinase plus microbubble group. The middle cerebral artery (MCA) was occluded by injecting autologous blood clots through the carotid artery. In the urokinase plus microbubble group, sulfur hexafluoride (SonoVue) microbubbles were injected intravenously immediately after intravenous injection of urokinase. The 2 groups were monitored by TCD from before until 2 h after thrombolysis, and the hemodynamic changes and infarct size were recorded.

Results

The urokinase alone group had 1 case of complete recanalization and 4 cases of partial recanalization (recanalization rate, 31.3%). The urokinase plus microbubble group had 3 cases of complete recanalization and 6 cases of partial recanalization (recanalization rate, 56.3%). The average size of the infarction foci was 13.9% in the urokinase group and 9.1% in the urokinase plus microbubble group (P = 0.025). Pathological examination revealed no cerebral hemorrhage in either group.

Conclusions

The addition of microbubbles enhanced the effects of transcranial Doppler ultrasound-assisted urokinase thrombolysis.     

Comparative analysis of fibrinolytic properties of Alteplase,Tenecteplase and Urokinase in an in vitro clot model of intracerebral haemorrhage

ObjectiveHematoma lysis with recombinant tissue plasminogen activator (rtPA) has emerged as an alternative therapy for spontaneous intracerebral and intraventricular haemorrhage (ICH and IVH). However, the MISTIE III and CLEAR III trial failed to show significant improvement of favourable outcomes. Besides experimental and clinical trials revealed neurotoxic effects of rtPA. The demand for optimization of fibrinolytic therapy persists. Herein, we used our recently devised clot model of ICH to systematically analyse fibrinolytic properties of rtPA, tenecteplase and urokinase.MethodsIn vitro clots of human blood (size: 25 ml and 50 ml; age: 1.5 tenecteplase, 24 tenecteplase and 48 tenecteplase) were produced and equipped with a catheter into the clot core for drug delivery and drainage. Various doses of tenecteplase and urokinase with different treatment periods were examined (overall 117 clots), assessing the optimal dose and treatment time of these fibrinolytics. Clots were weighed before and at the end of treatment. These results were compared with clots treated with 1 mg rtPA or with 0.9% sodium chloride solution.ResultsThe optimal treatment scheme of tenecteplase was found to be 100 IU with an incubation time of 30 min, for urokinase it was 50 000 IU with an incubation time of 20 min. The relative clot end weight of tenecteplase and urokinase (31.3±11.9%, 34.8 ±7.7%) was comparable to rtPA (36.7±10.7%). Larger clots were more effectively treated with tenecteplase compared to the control group (P=0.0013). urokinase and tenecteplase had similar lysis rates in aged clots and 90 min clots. One and two repetitive treatments with tenecteplase were as effective as two and three cycles of urokinase.ConclusionsIn our in vitro clot model we could determine optimal treatment regimens of tenecteplase (100 IU, 30 min) and urokinase (50 000 IU, 20 min). Urokinase and tenecteplase were comparable in their fibrinolytic potential compared to 1mg rtPA in small clots and showed an effective lysis in aged clots. tenecteplase was more effective in larger clots.     

Ultrasound-facilitated thrombolysis using tissue-plasminogen activator-loaded echogenic liposomes

INTRODUCTION: Targeted delivery of thrombolytics to the site of occlusion is an attractive concept, with implications for the treatment of many thrombo-occlusive diseases. Ultrasound enhances thrombolysis, which can be augmented by the addition of a contrast agent. We have previously reported development of echogenic liposomes (ELIP) for targeted highlighting of structures with potential for drug and gene delivery. This study evaluated the potential of ELIP for thrombolytic loading, and the effect of ultrasound exposure of thrombolytic-loaded ELIP on thrombolytic efficacy. MATERIALS AND METHODS: Tissue-plasminogen activator (tPA) was loaded into ELIP. Echogenicity was assessed and reported as mean grayscale values. Whole porcine clots were treated with plasma, free tPA, tPA+Optison (echocontrast agent), or tPA-loaded ELIP, with and without ultrasound (1 MHz, continuous wave, 2 W/cm(2), for 2 min). Clots were weighed before and after a 30-min treatment period, and results reported as percent clot mass loss. RESULTS: tPA entrapment into ELIP was feasible with 50% entrapment, and retention of echogenicity. Treatment with tPA-loaded ELIP resulted in effective clot lysis with an effect similar to treatment with free tPA. Ultrasound exposure of tPA-loaded ELIP resulted in enhanced thrombolysis (49.5% relative improvement vs. no ultrasound). Much of the ultrasound effect appeared to be related to drug release from the tPA-ELIP complex. CONCLUSIONS: We have demonstrated entrapment of tPA into ELIP with effective clot lysis and drug release using ultrasound. Our tPA-loaded ELIP has potential for specific highlighting of clots to confirm agent delivery and help focus ultrasound therapy for targeted ultrasound-facilitated thrombolysis.     

Insertion of fibrin peptides into urokinase enhances fibrin affinity

Low molecular weight two-chain urokinase is a 33-kD plasminogen activator, which has no innate affinity for fibrin and consequently, its use to facilitate lysis of blood clots may lead to systemic activation of plasminogen. In order to impart clot affinities to this urokinase form (UK) we have generated two novel fibrin-binding derivatives by partially reducing UK and exchanging the native disulfide-linked peptide A with peptide A analogs. The peptide A analogs contained the fibrin-adherent fibrin-derived sequences, GPRP (derived from positions 17-20 of the fibrinogen alpha chain) or QAGDV (407-411 sequence of the fibrinogen gamma chain), each coupled through amino-hexanoic acid to a synthetic peptide, LKFQCGQK, containing the Leu 144-Lys 158 sequence of the urinary plasminogen activator A Chain. The resultant derivatives contained about 0.4 moles peptide analog/mole UK, were 75% active toward synthetic UK substrates, and were recovered in a nearly 80% yield. The two fibrin peptide derivatives had a five-fold greater affinity for the clots.