Objective To evaluate the effect of astragaloside Ⅳ on postoperative cognitive function in aged rats.Methods Sixty healthy male Sprague-Dawley rats,aged 22 months,weighing 360-480 g,were divided into 4 groups(n=15 each)using a random number table:control group(group C),surgery group(group S),low-dose astragaloside Ⅳ group(group L-AGS)and high-dose astragaloside IV group(group H-AGS).At 3 days prior to surgery,astragaloside Ⅳ 20 and 40 mg/kg were injected intraperitoneally once a day in L-AGS and H-AGS groups,respectively.The equal volume of normal saline was given instead in C and S groups.The animals underwent splenectomy under anesthesia with 1.8% isoflurane in S,L-AGS and H-AGS groups.Five rats in each group were randomly sacrificed at 1 day after operation,the hippocampi were removed for determination of interleukin-1beta(IL-1β),tumor necrosis factor-alpha(TNF-α)and IL-6 contents(by enzyme-linked immunosorbent assay)and expression of activated caspase-3,Bax and Bcl-2(by Western blot).The left animals underwent Morris water maze test at 15 days after operation.Results Compared with group C,the escape latency was significantly prolonged,the frequency of crossing the original platform was reduced,the space exploration time was shortened,the expression of activated caspase-3 and Bax was up-regulated,the expression of Bcl-2 was down-regulated,and the IL-1β,TNF-α and IL-6 contents were increased after operation in group S(P<0.05).Compared with group S,the escape latency was significantly shortened,the frequency of crossing the original platform was increased,the space exploration time was prolonged,the expression of activated caspase-3 and Bax was down-regulated,the expression of Bcl-2 was up-regulated,and the IL-1β,TNF-α and IL-6 contents were decreased after operation in L-AGS and H-AGS groups(P<0.05).Compared with L-AGS,the escape latency was significantly shortened,the frequency of crossing the original platform was increased,the space exploration time was prolonged,and the TNF-α contents were decreased after operation in group H-AGS(P<0.05).Conclusion Astragaloside Ⅳ can improve the postoperative cognitive function in a dose-dependent manner in aged rats.