Blood pressure lowering action of active principle from Trachyspermum ammi (L.) sprague

Trachyspermum ammi (L.) Syn. Carum copticum (L.) Bth. (Apiaceae) is locally known as Ajowan. Bioassay-directed fractionation of Trachyspermum ammi has resulted in the isolation of thymol which is present in other plants as well. However, its action on blood pressure has not been studied so far. In anaesthetized rats, thymol (1-10mg/kg) produced dose-dependent fall in blood pressure and heart rate. These effects were not blocked by atropine (1 mg/kg) and thymol did not modify presser response of norepinepherine, which rules out the possibility of cholinergic stimulation or adrenergic blockade. In spontaneously beating atria, thymol caused decrease in force and rate of atrial contractions. These effects remained unaltered in the presence of atropine. In rabbit aorta, thymol caused relaxation of norepinepherine and potassium induced contractions in a concentration-dependent manner. These relaxant effects remained unchanged after the removal of endothelium. Moreover, atropine, propranolol, indomethacine and glibenclamide did not alter the vasorelaxation by thymol. These results suggest that Trachyspermum ammi contains a calcium channel blocker-like constituent (thymol) which may explain the hypotensive and bradycardiac effects observed in the in vivo studies.