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Berberine, when administered into a ear-vein of the rabbit anesthetized with urethane, produced a long-lasting, dose-related fall in blood pressure, but intraventricular berberine did not elicit the hypotensive response. This hypotensive activity of berberine was not influenced by pretreatment of vagotomization and atropine. Depressor responses induced by berberine were not impaired by diphenhydramine, chlorisondamine, guanethidine and propranolol, but reduced significantly by phentolamine pretreatment. Berberine attenuated markedly pressor responses of norepinephrine and epinephrine. These results suggest that berberine causes the hypotensive activity that is attributable to alpha adrenoceptor blockade, but not to a direct relaxant effect upon vascular smooth muscle.
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