Effects of tetrandrine on seven vascular smooth muscles

The effects of tetrandrine (Tet) on seven isolated vascular strips of rabbit were compared. The influence of Tet, verapamil (Ver) and phentolamine (Phen) on noradrenaline (NA) dose-response curves were studied. Tet injibited the contraction evoked by high K+ (60 mM) in thoracic aortic strips and more prominently in mesenteric arterial strips. Phen competiticely antagonized NA. Tet and Ver also antagonized NA but in a noneompetitive manner. Calcium was antagonized by Tet and Ver noncompetitively.
The findings suggest that the Tet-induced telaxation on vascular smooth muscle results from its antagonism to calcium, similar to verapamil.