Teucrium polium‑induced Vasorelaxation Mediated by Endothelium‑dependent and Endothelium‑independent Mechanisms in Isolated Rat Thoracic Aorta

Objective: There are some reports on hypotensive and antispasmodic effects of Teucrium polium L. (Lamiaceae) (TP). Subjects and Methods: The activity of different concentrations of TP extract (1, 2, 4 and 8 mg/ml) was evaluated on contractile responses of isolated aorta to potassium chloride (KCl) and phenylephrine (PE). Results: The cumulative concentrations of the extract induced a concentration‑dependent relaxation in the aorta precontracted by PE and KCl. Extract‑induced vasorelaxations in denuded aortic rings precontracted by PE and KCl at lower concentrations were considerably less than intact aortic rings, but this effect was significantly more at concentrations of 4 mg/ml for PE‑, 4 and 8 mg/ml for KCl‑induced contractions. All the extract concentrations (except 1 mg/ml) significantly relaxed PE‑induced contraction in the presence of NG‑nitro‑L‑arginine methyl ester. Indomethacin reduced effectively extract‑induced vasorelaxation at 1 and 2 mg/ml. The extract reduced PE‑ and KCl‑induced contractions in the presence of cumulative calcium concentrations and after incubation with diltiazem; this vasorelaxant effect of TP was decreased. TP‑induced relaxation was inhibited by heparin, ruthenium red, glibenclamide, and tetraethylammonium, but 4‑aminopyridine had no effect on TP‑induced relaxation. Conclusion: TP extract has vasorelaxant effect on isolated rat thoracic aorta which mediated by endothelium‑dependent and endothelium‑independent mechanisms. The relaxation mainly was mediated by inhibition of calcium influx in vascular smooth muscle cells. It seems that the vasorelaxant effect of extract at lower concentrations was mediated by nitric oxide and prostacyclin.