BLOOD-PRESSURE-LOWERING ACTION OF ACTIVE PRINCIPLE FROM TRACHYSPERMUM-AMMI (L) SPRAGUE

Trachyspermum ammi (L.) Syn. Carum copticum (L.) Bth. (Apiaceae) is lo cally known as Ajowan. Bioassay-directed fractionation of Trachyspermu m ammi has resulted in the isolation of thymol which is present in oth er plants as well. However, its action on blood pressure has not been studied so far. In anaesthetized rats, thymol (1-10 mg/kg) produced do se-dependent fall in blood pressure and heart rate. These effects were nor blocked by atropine (1 mg/kg) and thymol did not modify presser r esponse of norepinepherine, which rules out the possibility of choline rgic stimulation or adrenergic blockade. In spontaneously beating atri a, thymol caused decrease in force and rate of atrial contractions. Th ese effects remained unaltered in the presence of atropine. In rabbit aorta, thymol caused relaxation of norepinepherine and potassium induc ed contractions in a concentration-dependent manner. These relaxant ef fects remained unchanged after the removal of endothelium. Moreover, a tropine, propranolol, indomethacine and glibenclamide did not alter th e vasorelaxation by thymol. These results suggest that Trachyspermum a mmi contains a calcium channel blocker-like constituent (thymol) which may explain the hypotensive and bradycardiac effects observed in the in vivo studies.