RESUMO

The pharmacological activities of the water extract of Piper marginatum Jacq. (Piperaceae), a plant reputed in the Brazilian folk medicine for its analgesic/antiinflammatory, hemostatic and skin wound-healing properties, were assessed. Intraperitoneal injection (i. p.) of the extract (0.1 to 1 g/kg) in mice and rats caused piloerection, sialorrhea, lacrimation, muscle relaxation and dyspnea. At doses above 1 g/kg the extract caused respiratory arrest and death. Intravenous injection of the extract (0.1 to 0.5 mg/kg) into anesthetized rats caused a dose-related hypertension (by 27 to 48 %) that was blocked by prazosin (1 mg/kg) and yohimbine (2 mg/kg). Pithing, reserpine treatment and ganglionic blockade with hexamethonium (5 mg/kg) enhanced the effect. Oral treatment of unanesthetized rats and intragastric administration to anesthetized animals also produced hypertension. The sympathomimetic activity of the extract in isolated vas deferens, left atria and mesenteric arterial bed preparations paralleled that of noradrenaline, and was blocked to the same extent as noradrenaline by α-blockers. The plant extract (0.5 and 1 g/kg, p. o.) also reduced carrageenin-induced paw edema in rats by 80 to 90 % of the control, but it had less effect on the volume of exudate and leucocyte migration in carrageenin-induced pleurisy. Likewise, the extract had a small analgesic effect on the acetic acid-induced writhing test in mice. It is concluded that the antiedema effect of the plant extract is mainly related to its vasoconstrictor constituent(s). This sympathomimetic activity may explain the plant's reputed hemostatic properties when applied topically to bleeding skin wounds. The predominant vasoconstrictor component of P. marginatum detected in HPLC analysis was noradrenaline, whose activity is apparently preserved in the crude extract and produces vasoconstriction after oral administration.