Cardiovascular effects of Tabernaemontana pandacaqui

Intravenous injection of ethanolic extracts of the stem, leaf and flower of Tabernaemontana pandacaqui caused hypotension in pentobarbital anesthetized rats. At high doses (100-300 mg/kg), the flower extract showed a transient hypertensive effect preceeding hypotensive activity. The effects of the extracts on the heart rate of anesthetized rats correlated well with the negative chronotropic and inotropic activity observed with isolated atrium. The hypotensive activity was not inhibited by antihistaminic and antimuscarinic agents. The extracts had no effect on the pressor effects induced by norepinephrine or dual carotid occlusion. These results suggest that the hypotensive action of the extracts is not mediated through histaminic and muscarinic receptors stimulation, alpha-adrenoceptor blockade or interference of sympathetic transmission.