Vascular relaxing effect of Hydrocotyle umbellata L. is mediated by blocking of l-type Ca²⁺ channels

Hydrocotyle umbellata L. is a medicinal herb for the treatment of some health problems including hypertension, according to traditional medicine. Even so, its vascular effects and the pharmacological action mechanisms have not been analyzed.

This experiment aimed to analyze the effects of hydroalcoholic extract of Hydrocotyle umbellata L. (HEHU) on isolated vessels and verify the interaction of hibalactone (chemical marker) against Ca_v1.2 channels using molecular docking.

Vascular reactivity experiments were performed using rat aortas with (E⁺) or without endothelium (E^-) in an isolated organ bath. Computational molecular docking approaches were used to show the direct effect on L-type Ca²⁺ Channels.

HEHU (0-560 μg/mL) induced relaxation of the pre-contracted arteries in a concentration-dependent manner. The maximum effect was higher in E⁺ (76.8 ± 4.1%) as compared to E^- (47.3 ± 5.5%). Pre-treatment of E⁺ arteries with L-NAME or ODQ reduced the relaxation to similar level of E^- arteries. The treatment of arteries with MDL-12,330 A, diclofenac, propranolol and atropine did not change the relaxation induced by HEHU. The contraction caused by internal Ca²⁺ release induced by caffeine was reduced after HEHU treatment. Moreover, the HEHU also impaired the contraction induced by Ca²⁺ influx stimulated with phenylephrine or high KCl. The docking study demonstrated the effectiveness of hibalactone in blocking the Ca_v1.2 channel.

These findings show that HEHU induces vascular relaxation which is potentiated (but not dependent) by endothelial cells. Blocking of Ca²⁺ influx seems to be the main mechanism for the vascular effects of HEHU.