Vasorelaxant effect of Tribulus terrestris extract and fractions on isolated rat aortae

Tribulus terrestris (Zygophylaceae) has been used by traditional medicine as tonic, aphrodisiac and diuretic agent, as well as to treat cardiovascular diseases. However, the vascular effect of Tribulus terrestris fruits is poorly explored. Thus, the aim of this study is to assess effect of Tribulus terrestris fruit preparations on rat aortae. Dried crude ethanol deriving from Tribulus terrestris fruit extract (CE) was partitioned to produce hexane (HEX), dichloromethane (DCM), ethyl acetate (EtOAc), butanol (BuOH) and methanol/water-soluble (MWS) fractions. These preparations had their phytochemical profile assessed though UPLC-ESI-MS. Concentration-response curves plotted for CE, or for its fractions, were built in precontracted vessels with, or without, intact endothelium. Cumulative addition of both CE and its fractions (0.1-1,000 µg/mL) to a phenylephrine-induced precontracted vessel (10-7 M) promoted vasorelaxant effect in a concentration-dependent manner, and it did not depend on the vascular endothelium. EtOAc (1,000 µg/mL) applied to endothelium-denuded rings has fully inhibited phenylephrine-induced contractions. Likewise, EtOAC (1,000 µg/mL) added to nominally Ca2+-free depolarizing solution inhibited CaCl2-induced contractions. UPLC-ESI-MS analyses have indicated that EtOAC is rich in cinnamic acid amide derivatives. Altogether, the herein analyzed data suggest that the vasorelaxant effect of EtOAc can likely be attributed to the blockage of voltage-gated calcium channels.