Abstract

Piper guineense is a popular herbal medicine used to manage pains and arthritis among other indications in South-West Nigeria. Previous biological studies report anti-oxidant, anti-microbial and antidiabetic activities for the essential oil of the plant while studies on its acute toxicity profile, potential analgesic and anti-inflammatory activities were unavailable. This study investigated the antinociceptive and anti-inflammatory effect of the plant fruit volatile component and determines its acute toxicity profile in rodents in an attempt to rationalize the use of the plant in folkoloric medicine. Essential oil of fresh fruits of P. guineense obtained by hydrodistillation was emulsified with Tween 80 and evaluated for acute toxicity test (LD₅₀) through the oral (p.o.) and intraperitoneal (i.p.) routes in mice. The oil (50 to 200 mg/kg, i.p.) was tested for anti-nociceptive activity on the hot plate and acetic acid-induced writhing models in mice, while the anti-inflammatory activity was assessed on the egg albumin-induced rat paw oedema. The LD₅₀ values obtained were 693 mg/kg, i.p. and 1265 mg/kg, p.o. The oil dose-dependently caused significant (p<0.01) prolongation of reaction time on the hot plate comparable to positive control, morphine signifying central antinoceceptive effect, significantly (p<0.01) inhibited writhings induced by acetic acid analogous to diclofenac suggesting peripheral mechanism and caused significant (p<0.01) reduction in egg albumin-induced rat paw oedema comparable to dexamethasone, indicating anti-inflammatory activity. This study shows that the essential oil of P. guineense was moderately toxic, possessed significant antinociceptive and anti-inflammatory activities which can be used to rationalize the use of the plant in ethnomedicine.

Key words: Piper guineense, volatile oil, acute toxicity, hot plate, egg albumin.