Hypertension is associated with endothelial dysfunction characterized by decreased vasorelaxation. Our research group recently demonstrated that hydroalcoholic extract of Syzygium cumini leaves (HESc) reduces the blood pressure in spontaneously hypertensive rats (SHR). This study evaluated the ability of HESc and chloroform fraction (CF) in promoting vasorelaxation on resistance arteries rings. Endothelium-deprived superior mesenteric artery rings were suspended in organ baths containing warm perfusion medium that was continuously bubbled with carbogen and then the vasorelaxant ability of HESc and CF were assayed. The cumulative additions of HESc (0.1 to 10 mg/mL) caused a concentration-dependent relaxant response, in precontracted preparations by NE or KCl. CF (0.1 to 1.0 mg/mL) exhibited remarkable vasorelaxant activity in preparations endothelium-denuded pre-contracted with NE, in a concentration-dependent manner. The pretreatment of TEA did not decrease significantly in relaxation. The incubation of CF (0.25 and 0.5 mg/ml) reduced in a concentration-dependent way, the Emax induced by NE in mesenteric artery, however, did not altered the pD2 of the NE. Additionally, CF promoted concentration-dependent manner, maximal effect inhibition and also led to a significant rightward shift in the concentration-response curve for Ca2+ in endothelium-denuded rings. This finding indicates that S. cumini acts as a vasorelaxant agent and interfere with the responsiveness of vascular smooth muscle cell, probably acting on the regulation of intracellular Ca2+ levels through voltage-operated calcium channels.
Key words: S. cumini, calcium channels, vasorelaxant, medicinal plant, antihypertensive.
SHR, Spontaneously hypertensive rat; HESc, Hydroalcoholic extract; CF, Chloroform fraction; NE, Norepinephrine; VSMC, Vascular smooth muscle cell; Emax, Maximum effect; ROOC’s, Receptor-operated Ca2+ channels; VOOC’s, Voltage-dependent Ca2+ channels; BKCa, Large-conductance Ca2+ activated K+ channels; TEA, Tetraethylammonium.