ABSTRACT
Ocimum basilicum is a dicotyledonous shrub grown in most parts of Nigeria. Its medicinal properties had gained popularity in traditional medicine. In addition the leaves are eaten in soups in many homes. It consists of a well defined mixture of flavonoids, vitamins, amino acids, sugars, anions, linalool, tannins, rosmarinic acid, salicylic acid, essential oils, fats and terpenes. The acute oral toxicity [determination of median lethal dose (LD50)], in vitro and in vivo experiments of aqueous and methanolic extracts were done. Acute toxicity test of aqueous and methanolic extracts of Ocimum basilicum was carried out on mice. In this study, fasted mice were given 10, 100, 1000, 1600, 2900 and 5000 mg/Kg of both extracts. Median lethal dose (LD50) was 3807.89 and 2154.07 mg/Kg for aqueous and methanolic extracts respectively. The study to determine in vivo effect of Ocimum basilicum leaf extracts of the shrub was on the gastrointestinal transit time in conscious rats. In the in vivo experiment, fasted rats were given 20, 40, 60 and 80 mg/Kg of the extracts orally and fifteen minutes later, 0.5ml of 10% charcoal (BaSO4 .H2O) was administered into the conscious animals. The control group received the vehicle (normal saline) before the charcoal meal. In the in vitro experiment the effect of 4.00 X 10-6, 8.00 X 10-6, 1.60 X 10-5, 3.20 X 10-5, 6.40 X 10-5, 1.28 X 10-4, 2.56 X 10-4, 5.12 X 10-4, 1.024 X 10-3 and 2.048 X 10-3 g/ml of both aqueous and methanolic extracts on the frequency and strength of contraction of an isolated rabbit ileum was determined using a microdynamometer. The result of the study indicates that aqueous and methanolic extracts of Ocimum basilicum leaves delays the gastrointestinal transit and inhibits the strength and rate of gastrointestinal smooth muscle contraction in a dose dependent manner. To study the possible mechanisms of action of extracts, phentolamine (α- receptor blocker) at concentration of 4.00 X 10-10, 8.00 X 10-10, 1.6 X 10-9, 3.2 X 10-9, 6.4 X 10-9 and 1.28 X 10-8 g/ml was able to abolish the inhibitory effect of both extracts on smooth muscle contraction. As a result, its inhibitory effect on smooth muscle cells may be mediated via α-receptors located on the cell membrane.