Idris Oyemitan
Professor,Obafemi Awolowo University, Nigeria.
Title: Evaluation of Neuropharmacological Activity and Determination of Chemical Composition of the Essential Oil of Plectranthus Aegyptiacus Fresh Leaf in Mice
Biography
Biography: Idris Oyemitan
Abstract
Background: Plectranthus aegyptiacus is an ethnomedicinal plant found in South-west Nigeria where it is used to manage fever, sensory diseases and cough among other ailments. The objective of this study was to evaluate the neuropharmacological activities of the essential oil of P. aegyptiacus fresh leaf in mice in addition to determine the oil’s chemical composition. Method: Essential oil of P. aegyptiacus (EOPA) was extracted from fresh leaves of the plant by hydro-distillation and analyzed to determine its chemical composition. The LD50 of the oil was determined orally and intraperitoneally. The EOPA (50-200 mg/kg, i.p., n=6) was tested for novelty-induced behavioural (NIBs), anxiolytic, sedative, anticonvulsant and analgesic activities using standard protocols. The probable mechanism(s) of the effect of the EOPA on the various neural pathways were studied using various antagonists. Results obtained for the oil were statistically analyzed and compared to negative and positive controls. Results: The LD50 values obtained for the EOPA were 2154 and 490 mg/kg for the oral and intraperitoneal routes respectively. The EOPA significantly (p<0.05–0.01) inhibited all behavioural display, significantly (p<0.05-0.01) increased the time spent on the open arms of the elevated plus maze, blocked the hind limb tonic extension on the maximal electric shock and protected the mice against PTZ–induced mortality, significantly (p<0.05-0.001) shortened sleep latency and prolonged total sleeping time induced by ketamine (100 mg/kg), significantly (p<0.05)) reduced writhings caused by acetic acid (1% v/v) and significantly (p<0.05) increased the reaction time on the hot plate. Flumazenil (2 mg/kg) significantly (p<0.05) reversed the effect of the oil on NIBs; atropine, naloxone and cyproheptadine significantly (p<0.01-0.001) potentiated the inhibitory effect of the oil, while yohimbine did not alter the effect of the oil on NIBs. Major compounds identified in the oil were antioxine, germacrene-D and p-cimene.
Conclusion: The major effect of the oil was depression of the CNS and it demonstrated significant anxiolytic, sedative, anticonvulsant and analgesic activities in mice. The mechanism of action of the oil is suggested to be mainly augmentation of GABAergic neurotransmission. Furthermore, this research inferentially validated the pharmacological basis for the folkloric use of the plant
Keywords: Plectranthus aegyptiacus, chemical composition, central nervous system activities, antioxine.