1. Natural Product Research Division, Department of Biological and Biomedical Sciences,
Aga Khan University Medical College, Karachi-74800, Pakistan
2. Department of Pharmacology, Faculty of Pharmacy, University of Karachi, Karachi, Pakistan

(Received: July 2, 2007; Accepted: October 5, 2007)

ABSTRACT

   Terminalia bellerica has been used as a folk medicine in a variety of ailments including hypertension.  Our aim was to investigate the possible mechanism of its blood pressure (BP)-lowering effect.  The crude extract of Terminalia bellerica fruit (Tb.Cr) which tested positive for flavonoids, sterols and tannins induced a dose-dependent (10-100 mg/kg) fall in the arterial BP of rats under anaesthesia.  In isolated guinea-pig atria, Tb.Cr inhibited the force and rate of atrial contractions.  In rabbit thoracic aorta, Tb.Cr relaxed the phenylephrine (PE, 1 µM) and K+ (80 mM)-induced contractions as well as  suppressed the PE (1 µM) control peaks in the Ca++-free medium, similar to that caused by verapamil.  The vasodilator effect of Tb.Cr was endothelium-independent as it was not opposed by Nω-nitro-L-arginine methyl ester in endothelium-intact rat aortic preparations and it occurred at the similar concentration in the endothelium-denuded tissues.  These results indicate that Terminalia bellerica lowers BP through Ca++ antagonist mechanism and thus provides a sound mechanistic background for its medicinal use in hypertension.

Key words: Terminalia bellerica, antihypertensive, Ca++ antagonist