Hypotensive and vasorelaxant effects induced by the ethanolic extract of the Mimosa caesalpiniifolia Benth. (Mimosaceae) inflorescences in normotensive rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Caatinga is highly influenced by its seasonality. This species is endemic in the northeastern region, which is rich in plants with pharmacological potential. Many of these plants are used by the population and some of them have confirmed pharmacological properties. Mimosa caesalpiniifolia Benth. (Mimosaceae) is a native plant from northeastern Brazil׳s caatinga, popularly known as sabiá and cascudo. The tea from the inflorescence of this species is used by the population of the semi-arid for the treatment of hypertension, and the utilization of the plant bark for the staunching of bleedings and wound washing in order to prevent inflammation; also, the ingestion of the bark infusion is used in the treatment of bronchitis. However, its pharmacological effects and mechanisms of action have not yet been studied. The aim of the present study was to determine the effect of the ethanolic extract of M. caesalpiniifolia on the cardiovascular system in rats. MATERIAL AND METHODS: In a study for the assessment of the hypotensive effect of the extract, the polyethylene catheters were inserted in the aorta artery and inferior vena cava for the measurement of the arterial pressure and heart rate. When intragastric administration was performed, only one catheter was implanted in the abdominal aorta. In studies for the vasorelaxant activity, mesenteric arterial rings (1-2mm) were used: they were kept in Tyrode׳s solution (95% O2 and 5% CO2) and submitted to tension of 0.75 g/f for 1h. The results were expressed as mean ± S.E.M., significant to the values of p<0.05. RESULTS: The administration of the doses through venous pathway (6.25; 12.5 and 25mg/kg, i.v.) promoted hypotension followed by bradycardia in the higher doses. The pre-treatment with atropine (2mg/kg, i.v.) interrupted both the hypotension and the bradycardia; with hexamethonium, hypotension was reverted and bradycardia was attenuated. While the administration of tea/flowers (25mg/kg i.v.) also promoted a following section of hypotension, a slight increase in heart rate was observed. When administered orally, MC-EtOH/flowers (100mg/kg, v.o.) promoted a decrease in the arterial pressure from 90 min on, without a significant alteration in the heart rate in relation to the control. In the in vitro study, a pharmacological trial was performed with the extracts obtained from parts of the species M. caesalpiifolia (leaves, bark, fruit and inflorescences). Among all extracts tested, the ethanolic extract from the inflorescences (MC-EtOH/flowers) presented higher vasorelaxant potency in relation to the other parts of the plant. Henceforth, MC-EtOH/flowers was used in the sequence. In mesenteric preparations pre-contracted with phenylephrine (10(-5)M), the MC-EtOH/flowers (0.1-750 µg/ml) promoted vasorelaxant effect regardless of the vascular endothelium. MC-EtOH/flowers inhibited the contractions induced by the cumulative addition of phenylephrine (10(-9)-10(-5)mol/l) or CaCl2 (10(-6)-3 × 10(-2)M), in a concentration-dependent way. In contractions induced by S(-)Bay K 8644, a Cav-L activator, the MC-EtOH/flowers promoted concentration-dependent relaxation, corroborating previous results. CONCLUSION: The tea of flowers of M. caesalpiniifolia promotes hypotension and tachycardia, whereas ethanolic extract (MC-EtOH) promotes hypotension and bradycardia involving the participation of the muscarinic and ganglionic pathways, as well as vasorelaxant action involving the Ca(2+) influx inhibition blockade.