Hypotensive action of an aqueous extract of Pimenta dioica (Myrtaceae) in rats

RESUMO

The intra-venous (i.v.) hypotensive action of the final aqueous fraction of Pimenta dioica was studied in Spontaneously Hypertensive Rats (SHR). The rats were anaesthetized (sodium pentobarbital 50 mg/kg), the trachea, right carotid artery and jugular vein were cannuated for adequate ventilation, direct blood pressure measurement and intra-venous administration of extract, solutions and drugs. The arterial line was connected to a pressure transducer (Viggo-Spectramed model P23 XL) and a polygraph (Grass model 7H) and monitored continuously during the firts five minutes after plan extract administration and then at 5 and 15 minute intervals for one hour. Responses were taken as the maximum pressure changes observed during this period. Increasing doses of the final aqueous fraction were given i.v. to groups of six SHR each. It produced a dose dependent decrease in blood pressure and the ED50 was 45 mg/kg. To discard that the hypotensive effect of the extracts was due to its ionic composition, a solution containing KCl, NaCl, CaCl2 adn MgCl2 equivalent to hte ion contents present in a dose of 50mg/kg of total asqueous extract was injected to Sprague-Dawley rats (SDN) using the same method as described above. It did not produce singificant changes in blood pressure. Pharmacological antagonistic studies were done injection either autonomic ganglion,alfa adrenoceptor,beta adrenoceptor and cholinergic receptor blockers prior to extract administration in SHR rats. Atropine, propranolol and phentolamine did no affect the hypotensive effect to the final aqueous fraction. With hexamethonium (autonomic ganglion blocker) the hypotensive response was diminished in a significant way (p<0.05). The hypotensive action of the final aqueous extract was not mediated through cholinergic, alfa o beta adrenergic receptors. The extract may posses vasorelaxing activity which could no be eviden after autonomic ganglion blockade due to extreme vasodilation present prior to extract administration. Future studies should address the question of a possible direct vasodilating effect of the extracts. Key words: Pimenta dioica, traditional medicine, herbal medicine, antihypertensive effect, arterial hypertension