Abstract: AIM: To study factors influencing mannitol to induce blood-brain barrieropening. METHODS: By constant flow pump, mannitol with different concentrationwas infused into left internal carotid artery of adult Wistar rats via their left external carotid artery at different speed, time.Firstly, after mannitol with a concentration of25%was transfused, the optimal open time of BBB was investigated using Evans blue as an indicator by injection at different time.Then influences of concentration of mannitol, speed of infusion, change of time on mannitol to induce BBB opening were studied. Finally, death rate was counted according to sex, body weight in order to observe the influence of sex, body weight on tolerance of rats. RESULTS: The open degree of BBB was optimal after2min when3.6ml mannitol with a concentration of25%was infused in30s at a speed of0.12ml·s,.However, mannitol with a concentration of20% did not almost have any effect on opening of BBB.Slowing of infusion speed or shortening of infusion time of mannitol reduced opening degree of BBB.Body weight affected rat tolerance to mannitol, the tolerance of the rat was higher in those with higher weight. CONCLUSION: The factors influencing mannitol to induce BBB opening are as follows:concentration, infusion speed, keeping time of mannitol.And the tolerance to mannitol is not concerned with the sex of the rats, but the body weight of the rats

Key words: pharmacology, mannitol, blood-brain barrier, rat