The effect of HA was not disap peared by pretreatment with H_ receptor blocker, cimitidine or α_ receptor b locker, yoh预先icvH 受体阻断剂甲氰咪胍 ,或α 受体阻断剂Yohinbin(育亨宾 )对HA的中枢心血管效应均无影响。