Some cardiovascular effects of the aqueous extract of the leaves of Starchytarpheta jamaicensis L. (Vahl)

Traditionally, many herbal doctors claim, some plants are known for their anti-hypertensive effects. The high patronage of sellers of such herbs may be an indication of the plants efficacy. However, their mechanisms of action as well as the active constituents may not have been documented.

The efficacy of powdered Stachytarpheta jamaicensis (L.) Vahl. leaves, known for treating hypertension in some Nigerian communities, was investigated in anaesthetized normotensive male rabbits. The extract was administered intravenously at doses ranging from 2.5–80mg/kg. The extract caused a dose-dependent fall in blood pressure and heart rate. 2.5mg/kg of the extract reduced the mean arterial pressure (MAP) from the initial 102.8±4.2mmHg to 96.6±7.3mmHg and the heart rate (HR) from 398.3±8.3 beats/min to 373.1±9.7 beats/min. 80mg/kg reduced MAP and HR to 38.9±3.1mmHg and178.3±83.7beats/min respectively.

The results showed that the water extract has a significant dose-dependent hypotensive effect. It has been shown in this study that the extract may not be acting through histamine release or through the stimulation of muscarinic receptors. Neither atropine nor promethazine inhibited the hypotensive effect of the extract. The acute hypotensive effect of the extract may be partly due to the negative chronotropic effect or to a direct effect on vascular smooth muscle.