Acta Poloniae Pharmaceutica ñ Drug Research, Vol. 64 No. 6 pp. 547ñ552, 2007

ISSN 0001-6837 Polish Pharmaceutical Society

HYPOTENSIVE EFFECT OF AQUEOUS EXTRACT OF THE LEAVES OF PHYLLANTHUS AMARUS SCHUM AND THONN (EUPHORBIACEAE).
*FABIAN C. AMAECHINA and ERIC K. OMOGBAI Department of Pharmacology and Toxicology, University of Benin, Benin City, Nigeria
Abstract: The plant of Phyllanthus amarus is used as diuretic and to lower blood pressure in traditional medicine practice. The effect of the aqueous extract of the leaves of Phyllanthus amarus on blood pressure was evaluated in normotensive male rabbits. Intravenously administered aqueous doses (5 mg to 80 mg/kg) of the extract to anaesthesized normotensive male rabbits produced a significant fall in mean diastolic, systolic and mean arterial pressures in a graded dose response manner. The dose of 5 mg/kg produced the least hypotensive effect, causing a fall in mean diastolic, systolic, and mean arterial pressure of 13.3 ± 3.1, 19.7 ± 5.4, and14.3 ± 3.4 mmHg, respectively, while the dose of 80 mg/kg produced the greatest fall in mean diastolic, systolic, and mean arterial pressure of 49.7 ± 7.9, 45.5 ± 9.5, and 48.00 ± 6.5 mmHg, respectively. The extract had a greater blood pressure depressant effect on the diastolic blood pressure than on the systolic blood pressure. The highest dose of 80 mg/kg caused 62.5% fall in diastolic blood pressure, compared to the 33.2% fall in systolic blood pressure caused by the same dose. Atropine at the dose of 1 mg/kg blocked the hypotensive effect of the aqueous extract in a competitive manner. Promethazine at the dose of 1 mg/kg did not block the hypotensive effect of the aqueous extract, but potentiated the effect of the extract. After the administration of promethazine, the maximum tolerable dose of the extract was 40 mg/kg as compared to the initial dose of 80 mg/kg. The