Cardiovascular effects of an extract from the roots of a shrub Elaeophorbia drupifera

A crude extract was prepared from the roots of E. drupifera. Lethality studies in mice showed a dose‐mortality relationship with an LD50 of 145 mg/kg mice i.p. The extract (2–260 µg/kg. i.v.) was tested in graded doses on the blood pressure and heart rate of urethane anaesthetized rats. The results showed that the extract decreased both the blood pressure and heart rate in a dose‐dependent manner. The maximum decrease in blood pressure (control, 78.3 ± 6.5 mmHg) and heart rate (control, 120.2 ± 5.5 beats/min) produced by the extract was about 46.2% and 41.7% (% control), respectively. Blocking the beta adrenoceptors with propranolol (0.5 µg/kg. i.v.) did not prevent the action of the extract on both the blood pressure and heart rate, suggesting that the extract was acting at a different site. This view was supported by the observation that the extract significantly depressed the increase in blood pressure and heart rate caused by bilateral occlusion of the common carotid artery. Also, the extract was found to prolong ACh‐induced hypotension in the rats. In animals pretreated with atropine sulphate (0.2 mg/kg. i.v), the extract was less effective in depressing the blood pressure. However, this atropine antagonism was surmounted by raising the concentration of the extract. Finally, in vitro studies using isolated arterial strips revealed that the extract also had a relaxant effect on vascular smooth muscle. This relaxant effect was dose‐dependent and was attenuated and/or abolished by phentolamine (0.5 µg/mL). Also, the extract relaxed aortic strips precontracted with noradrenaline (1 × 10−7 mol L−1) but failed to relax strips precontracted with KCl (50 mmol/L). We conclude that the crude extract from the roots of E. drupifera probably contains acetylcholine‐like agent(s) which interferes with the cholinergic mechanism, as well as catecholamine‐like agent(s) exhibiting mainly alpha‐adrenoceptor activity. Copyright © 1999 John Wiley & Sons, Ltd.