3 讨论 EGb 761主要含有黄酮苷(24%)和萜类内酯(6%)两种成分。黄酮类化合物主要有槲皮素、山奈黄素、异鼠李素。萜类内酯除银杏内酯外还有银杏苦内酯A、B、C和J。该制剂可抗脂质过氧化,对缺血和(或)缺氧损伤、机械损伤的神经元具有保护作用。它能减轻谷氨酸毒性,抑制血小板凝集,对抗凋亡,还能使眼动脉血流量增加。本研究结果证明EGb 761能抑制视神经横断后RGC凋亡,对RGC有保护作用,该结果与Hirooka等[11]的研究结果一致。 PERG是客观评价RGC功能的方法之一,其波形主要特征为一个正向的P50波和一个向下的N95波。根据各种疾病PERG的不同表现,Holder[12]认为两个波的起源不同。药理学分析也证明,N95波可被河豚毒素完全阻断,N95波依赖于RGC产生的动作电位。尽管P50波的确切起源还不清楚,并不能被河豚毒素阻断,但在青光眼患者和猴青光眼模型中P50波振幅均有所下降,因此推测它可能起源于RGC的胞体和(或)RGC的远端[13]。以往评价慢性高眼压引起的RGC数目减少常常采用闪光ERG[14],然而闪光ERG只代表视网膜外层电反应,PERG才真正代表视网膜内层电反应[15, 16]。迄今,尽管对PERG的确切起源尚未完全清楚,但起源于视网膜内层是一致公认的,主要是RGC[17]。Berardi等[18]证实横断大鼠视神经后可引起RGC逆行性变性,导致PERG反应消失,而闪光ERG不受影响。目前PERG已被应用于临床评价高眼压症和青光眼患者的视功能,并认为青光眼对PERG的N95的影响比P50大[19, 20]。BenShlomo等[9]首次应用PERG评价大鼠高眼压后RGC功能,并研究N95振幅和RGC数目的相关性,结果发现两者呈正相关关系。我们的研究也证明豚鼠视神经横断后,随着RGC数目的减少N95振幅逐渐降低,且两者呈正相关关系(r=0.858 68,P=0.001 5),表明PERG的N95振幅可评价RGC数目丧失的程度。 总之,腹腔注射EGb 761可抑制视神经横断后RGC凋亡,从而保护RGC的结构和功能。PERG是评价视神经横断后RGC丧失程度的有效指标之一。
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