Abstract: AIM: To compare the peculiarity of effects between moxonidine and clonidine on decreasing blood pressure in spontaneous hypertensive rats (SHR). METHODS: Arterial blood pressure and heat rate were directly determined by a catheter on the carotid artery or indirectly determined by a tail-cuff method in conscious and anesthetized SHR after once or repeatedly oral administration, respectively.RESULTS: Moxonidine showed a dose-dependent effect on reducing blood pressure and heat rate after once large dose oral administration in conscious SHR.The effect on decreasing blood pressure and heart rate after oral administration of 10 mg·kg^-1moxonidine was equal to the effects after oral administration of 1 mg·kg^-1clonidine.The rate of reducing blood pressure by moxonidine was equal to that by clonidine, and the decreasing in heart rate was little and short after repeatedly small dose oral administration of moxonidine.Moxonidine exerted a dose-dependent effect on reducing blood pressure after small dose oral administration in anesthetized SHR.There was no significant difference between moxonidine and clonidine in reducing rate of blood pressure after same dose administration (P>0.05).CONCLUSION: The effects of 10mg·kg^-1moxonidine on reduced blood pressure and heart rate in SHR is equal to the effects of 1mg·kg^-1clonidine after once large dose oral administration.There is no significant difference between the moxonidine and clonidine of the same dose in reducing blood pressure after repeatedly small dose oral administration in SHR.

Key words: moxonidine, clonidine, SHR, hypertension, antihypertensive drug