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To investigate the effects of Siegesbeckiae Herba on the blood pressure, this study was carried out in the whole and the spinal rabbits, using its water and ethanol extracts. When Siegesbeckiae Herba water extract (SGWE) and ethanol extract (SGEE) were administered into the whole rabbits by route of ear vein, both of them produced fall of blood pressure. The difference between these two extracts was that SGEE is more potent than SGWE. The depressor effects of SGWE and SGEE were not affected by vagotominization but inhibited by pretreatment of atropine. The depressor responses of the whole rabbits to intravenous SGWE and SGEE were weakened by treatment of animals with bethanidine or phentolamine but not by propranolol. Pretreatment of the whole rabbits with diphenhydramine significantly weakened the depressor effects of SGEE. Infusion of SGWE and SGEE in the whole rabbits did not influence the presser effects caused by angiotensin, norepinephrine or carotid artery occlusion. SGEE, when given into the lateral ventricle of the whole rabbits or into the vein of the spinal rabbits, elicited fall of blood pressure, respectively.
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