BACKGROUND: Wu long dan is the experienced formula summarized in the long-term clinical practice on the treatment ischemic cerebral vascular disorder and aims at "benefiting qi,strengthening spleen,tonifying kidney,activating blood circulation,promoting circulation of collaterals and resolving phlegm". It is indicated in the previous researches that such formula acts on improving microcirculation of cerebrum,regulating neural endocrinal system and being against cerebral ischemic injury. The increased blood viscosity and disturbance endothelin and nitric oxide(NO) secreted from vessels and nerve cells have participated in the pathological progression of multi-infarct dementia(MID) and affect mutually.OBJECTIVE: To probe into the effect of wu long dan on blood viscosity,NO and endothelin in MID model in rats by duplicating MID rat model.DESIGN: A randomized controlled and experimental study based on the experimental animals.SETTING: Department of traditional Chinese medicine in a military medical university of Chinese PLA.MATERIALS: The experiment was performed in Laboratory of Department of Traditional Chinese Medicine in First Military Medical University of Chinese PLA and Laboratory of Department of Neurological Internal Medicine in affiliated Zhujiang Hospital from January to August 2002. SD male rats of clean grade were employed,weighted(270 ± 30) g (Qualified No. 2000337). In the experiment,there were blank control,model group,wu long dan low dosage group and wu long dan high dosage group.METHODS: After internal carotid artery isolated,dried blood suspension of homologous rats was injected at the ratio of 1:200 to prepare MID rat model. Cone-plate stationary method was adopted for the determination of blood viscosity,radioimmunoassay was for the determination of endothelin and cadmium-reduction-colorimetric method was for NO determination. Water-alcohol sedimentation was for the preparation of wu long dan.MAIN OUTCOME MEASURES: Primary indexes: whole blood viscosity,plasma viscosity,plasma endothelin and NO concentration in every experimental group. Secondary indexes: results of learning and memory test.creased significantly (200 s-1: 7.21 ± 1.02; 5 s-1: 11.24 ± 0.93,P ＜ 0.01 ),the plasma endothelin(ng/L) content(167.91 ±46. 87,P ＜0.01) and endothelia/NO(64.94 ± 11.14,P ＜0.01) were increased,and NO(μmol/L)(2.60 ± 0. 43,P ＜ 0.01 ) reduced. The significant difference in the vismedication group in rats(in high dosage 200 s-1: 4.28 ±0. 81,5 s-1:8.84±0.79,P ＜0.01; in low dosage 200 s-1: 5.22±0.92,5 s-1;9.18 ± 0. 81,P ＜ 0.05 ) with model group. Concerning to plasma endothelin(ng/L) (in high dosage 120. 18±34.51,P ＜ 0.01),NO (μmol/L)content(6.84 ± 0.79,P ＜ 0.01 ) and endothelin/NO(31.26 ± 8.41,P＜ 0.01 ),the significant differences presented in all of those compared with model group.CONCLUSION: The increased blood viscosity and the disturbance between endothelin and NO secreted from vessels and nerve cells have participated in the pathological progression of multi-infarction MID and affect mutually. Wu long dan with the efficacy of strengthening spleen and tonifying kidney,activating blood circulation,resolving phlegm and promoting the circulations of collaterals acts on antagonism and regulation of increased blood viscosity and abnormal secretion of NO and endothelin in MID model rats.