Mechanisms underlying the vascular relaxation activities of Zingiber officinale var. rubrum in thoracic aorta of spontaneously hypertensive rats

OBJECTIVE: To evaluate vasorelaxant and vasoconstriction effects of Zingiber officinale var. rubrum (ZOVR) on live rats and isolated aortic rings of spontaneously hypertensive rats (SHRs).

METHODS: Extracts of ZOVR were subjected to in-vivo antihypertensive screening using noninvasive blood pressures in SHRs. The most potent extract, ZOVR petroleum ether extract (ZOP) was then fractionated using n-hexane, chloroform and water. Isolated thoracic aortic rings were harvested and subjected to vascular relaxation studies of n-hexane fraction of ZOP (HFZOP) with incubation of different antagonists such as Nω-nitro-l-arginine methyl ester (L-NAME, 10 µmol/L), indomethacin (10 µmol/L), methylene blue (10 µmol/L), atropine (1 µmol/L), glibenclamide (10 µmol/L), prazosin (0.01 µmol/L), and propranolol (1 µmol/L).

RESULTS: During the screening of various ZOVR extracts, ZOP produced the most reduction in blood pressures of SHRs and so did HFZOP. HFZOP significantly decreased phenylephrine-induced contraction and enhanced acetylcholine-induced relaxation. L-NAME, indomethacin, methylene blue, atropine, and glibenclamide significantly potentiated the vasorelaxant effects of HFZOP. Propranolol and prazosin did not alter the vasorelaxant effects of HFZOP. HFZOP significantly suppressed the Ca2+-dependent contraction and influenced the ratio of the responses to phenylephrine in Ca2+-free medium.

CONCLUSION: This study demonstrates that ZOP may exert an antihypertensive effect in the SHR model. Its possible vascular relaxation mechanisms involve nitric oxide and prostacyclin release, activation of cGMP-KATP channels, stimulation of muscarinic receptors, and transmembrane calcium channel or Ca2+ release from intracellular stores. Possible active compounds that contribute to the vasorelaxant effects are 6-gingerol, 8-gingerol and 6-shogaol.