Objective To investigate the mechanism of the permeability change in the blood brain barrier(BBB)at early stage of infectious brain edema which was pretreated with LPS.Methods PMNs were isolated and purified.The concentration of Glu was measured in the supernatant without cells.The rat BMECs were primarily isolated and cultured.The permeability of BMECs waB evaluated by measuring the passing rate of 125 I-BSA via γ ray counter.The expression of NMDAR1 on BMECs was evaluated.Results The concentration of Glu in the LPS preconditioning PMNs subgroup at 5 rain time point was highest.In each group conditioned for 240 min,the permeability index of Bake average of the LPS preconditioning PMNs extract group was highest(P＜0.01).The expression of NMDARI increased in the LPS preconditioning PMNs extract group was more than that in other groups.Conclusions The research showed for the first time that the concentration of Glu increased after LPS preconditioning and the Glu excreted by PMNs can promote the permeability of BMECs and change the function of BBB,which possibly may be related the mechanism of NMDAR1 expression increased in BMECs.