ABSTRACT
As the search for, and development of new drugs continues, drug companies engage in the large-scale pharmacological screening of medicinal plants. This creates the need to elucidate the mechanism of action of medicinal plants found to possess biological activity as a means of deriving their full therapeutic potential. This research was carried out to investigate the mechanism of the antihypertensive action of Vernonia amygdalina, Ocimum gratissimum, and Pterocarpus erinaceus using animal models. The dried 70% ethanolic extracts of the plants were prepared at varying concentrations ranging from 0.4 mg/mL to 50 mg/mL. These extracts were administered at varying doses alone and in the presence of selected antagonists like prazocin in anesthetized cat in-vivo and to rabbit jejunum and spontaneously beating guinea pig right atrium. Adrenaline and atropine were used as control drugs.The effects of these plants extracts were demonstrated on the Finkleman preparation and they were found to induce relaxation of the rabbit jejunum. They also reduced both the rate and force of contraction of spontaneously beating guinea pig's right atrium. The cardiovascular effects of the extracts were investigated on cat blood pressure. The effect of atropine tested in the presence of V. amygdalina and O. gratissimum showed a change in the pattern of induced fall in blood pressure but does block the fall in blood pressure induced by the extracts. While the exact mechanism of the antihypertensive action of these extracts has not been fully determined, the result of this research work proposes that the mechanism could either be blocking calcium channels or have direct activity on lowering blood pressure. It is therefore recommended that further studies be conducted on the extracts to better understand the mechanism of antihypertensive actions of these plants.