Objective To study the possible mechanism of Phlegm-Transforming Network Vessels-Freeing Formula in preventing and treating bleeding after thrombolytic therapy with recombinant tissue plasminogen activator（rt-PA）in acute cerebral infarction.Methods Totally 240 SD rats were randomized into the sham operation group

model group

rt-PA group and low-dose

middle-dose

and high-dose Chinese medicinal groups.The middle cerebral artery occlusion models were established with self-embolism.The low-dose

middle-dose

and high-dose Chinese medicinal groups were injected 5.67mg/kg of rt-PA through the tail vein 3 hours after thrombus injection.After thrombolytic therapy

the low-dose

middle-dose and high-dose Chinese medicinal groups were gavaged with 0.72g/kg

1.44g/kg and 2.88g/kg concentrated solution of PhlegmTransforming Network Vessels-Freeing Formula

respectively.The rt-PA group was gavaged with equal amount of normal saline after thrombolytic therapy.The sham operation group and model group were gavaged with equal amount of normal saline at the same time point.Each group was given intragastric administration twice daily for 7 days.The morphology of endothelial cells in ischemic region of cerebral cortex was observed with electron microscopy at the 6th

24th and 72nd hour and on the 7th day of experiment.The expressions of occluding

claudin-1 and ZO-1 proteins were detected with Western blotting.Results Comparing with the sham operation group

the expressions of occluding

claudin-1 and ZO-1 proteins were significantly decreased at the 24th and 72nd hour and on the 7th day of experiment in the model group（P<0.05）.Comparing with the model group

the expressions of occluding and claudin-1 proteins were significantly increased at the 6th

24th and 72nd hour of experiment in the high-dose Chinese medicinal group（P<0.05）

and the expression of occluding protein was significantly increased at the 24th and 72nd hour of experiment in the middle-dose Chinese medicinal group（P<0.05）.Comparing with the rt-PA group

the expression of occluding protein was significantly increased at the 24th and 72nd hour of experiment in the middle-dose and high-dose Chinese medicinal groups（P<0.05）.The expression of claudin-1 protein at the 72nd hour of experiment and the expression of ZO-1 protein at the 24th hour of experiment in the middle-dose Chinese medicinal group was significantly higher than that in the rt-PA group respectively（P<0.05）.Conclusion Phlegm-Transforming Network VesselsFreeing Formula may protect the integrity of blood brain barrier by improving the morphology of endothelial cells in cerebral cortex and regulating the expressions of occluding

claudin-1 and ZO-1 proteins.