Differential Effect of Tetrandrine on Aortic Relaxation and Chronotropic Activity in Rat Isolated Aorta and Atria

Abstract

Tetrandrine is known as a calcium blocker which can induce bradycardia as well as hypotension. It was however reported that the heart rate was unchanged during tetrandrine-induced hypotension. The possibility of different tissue sensitivity to various concentrations of tetrandrine was therefore investigated using the rat isolated aorta and atria. It was found that tetrandrine (1 × 10^-5M) was sufficient to suppress more than 90% of the aortic contraction induced by norepinephrine (1 × 10^-8M) or KCl (50 mM). However, only 10% of the initial heart rate was suppressed by 1 × 10^-5M tetrandrine. It was therefore concluded that the aorta and atria might have different sensitivity to tetrandrine.