Vasodilatory Effect of Alpinia officinarum Extract in Rat Mesenteric Arteries

Abstract

Background: Alpinia officinarum (A. officinarum) is known to exhibit a beneficial effect for anti-inflammatory, anti-oxidant, and anti-hyperlipidemic effects. However, no sufficient research data are available on the cardiovascular effect of A. officinarum. Thus, in this study, we investigate whether A. officinarum extract has direct effects on vascular reactivity.

Methods: To examine whether A. officinarum extract affects vascular functionality, we measured isometric tension in rat mesenteric resistance arteries using a wire myograph. After arteries were pre-contracted with high-K⁺ (70 mM), phenylephrine (5 µM), or U46619 (1 µM), A. officinarum extract was treated.

Results: A. officinarum extract induced vasodilation in a concentration-dependent manner, and this effect was endothelium independent. To further investigate the mechanism, we incubated arteries in a Ca²⁺-free and high-K⁺ solution, followed by the cumulative addition of CaCl₂ (0.01-2.5 mM) with or without A. officinarum extract (30 µg/mL). Pre-treatment of A. officinarum extract reduced the contractile responses induced by cumulative administration of Ca²⁺, which suggests that extracellular Ca²⁺ influx was inhibited by the treatment of A. officinarum extract. These results were associated with a reduction in phosphorylated MLC₂₀ in VSMCs treated with A. officinarum extract. Furthermore, eucalyptol, an active compound of A. officinarum extract, had a similar effect as A. officinarum extract, which causes vasodilation in mesenteric resistance arteries.

Conclusion: A. officinarum extract and its active compound eucalyptol induce concentration-dependent vasodilation in mesenteric resistance arteries. These results suggest that administration of A. officinarum extract could exert beneficial effects to treat high blood pressure.

Keywords: Alpinia officinarum; Ca2+; eucalyptol; mesenteric resistance arteries; relaxation; vasodilation.

Figure 1

A. officinarum extract-induced vasodilation in rat mesenteric arteries. (A₁–C₁), data showing responses to cumulative administration of A. officinarum extract (1–100 μg/mL) on high-K⁺ (A₁) or U46619 (B₁) or phenylephrine (C₁) -induced contraction. (A₂–C₂), statistical analysis of the relaxation response to A. officinarum extract. Mean ± SD (n = 7). Inset, representative trace showing responses to vehicle, DMSO (0.0005–0.05%). (W/O: wash out; AO: Alpinia officinarum extract).

Figure 1

A. officinarum extract-induced vasodilation in rat mesenteric arteries. (A₁–C₁), data showing responses to cumulative administration of A. officinarum extract (1–100 μg/mL) on high-K⁺ (A₁) or U46619 (B₁) or phenylephrine (C₁) -induced contraction. (A₂–C₂), statistical analysis of the relaxation response to A. officinarum extract. Mean ± SD (n = 7). Inset, representative trace showing responses to vehicle, DMSO (0.0005–0.05%). (W/O: wash out; AO: Alpinia officinarum extract).

Figure 2

Endothelium-independent vasodilation induced by A. officinarum extract. (A), A. officinarum extract-induced vasodilation in the endothelium intact mesenteric arteries. (B), A. officinarum extract-induced vasodilation in the endothelium denuded mesenteric arteries. (C), A. officinarum extract-induced vasodilation in the presence of eNOS inhibitor L-NNA (500 μM). (D), A. officinarum extract-induced vasodilation in the presence of eNOS inhibitor L-NAME (300 μM). (E), statistical analysis of A. officinarum extract-induced vasodilation. Mean ± SD (n = 5). (Ach: acetylcholine; W/O: wash out; AO: Alpinia officinarum extract; L-NNA: N-ω-Nitro-L-arginine; L-NAME: N-ω-Nitro-L-arginine methyl ester).

Figure 3

Effect of K⁺ channel blockers on A. officinarum extract-induced vasodilation. (A), effect of A. officinarum extract in the mesenteric artery pre-contracted with U46619 (1 μΜ). (B–E), effect of A. officinarum extract in the presence of TEA (B), or BaCl₂ (C), or glibenclamide (D), or 4-AP (E). (F), statistical analysis of the relaxation response of A. officinarum extract in the presence of various K⁺ blockers. Relaxation of arteries is expressed as the percentage of the contraction induced by U46619 (1 μΜ). Mean ± SD (n = 5). (AO: Alpinia officinarum extract; TEA: tetraethylammonium; Gli: glibenclamide; 4-aminopyridine: 4-AP).

Figure 4

Decrease in Ca²⁺-induced contraction in A. officinarum extract-treated mesenteric arteries. (A), Representative trace showing the effect of A. officinarum in the mesenteric arteries, treated with cumulative addition of CaCl₂ (0.1–2 mM). (B), statistical analysis of contraction induced by CaCl₂ in the mesenteric arteries, with or without A. officinarum. Mean ± SD (n = 7). ** p < 0.01, *** p < 0.001 (CPA: cyclopiazonic acid; W/O: wash out; AO: Alpinia officinarum extract).

Figure 5

Effect of A. officinarum extract on the phosphorylation of 20 kDa myosin light chain (MLC₂₀). (A), representative Western blot analysis for phosphorylated MLC₂₀ (phospho–MLC₂₀) and total MLC₂₀ (total–MLC₂₀) in control VSMCs, VSMCs treated with phenylephrine (5 µΜ), and VSMCs co-treated with phenylephrine (5 µΜ) and A. officinarum (30 µg/mL). (B). Quantitative data for phosphorylated MLC₂₀. * p < 0.05 (AO: Alpinia officinarum extract).

Figure 6

Eucalyptol-induced vasodilation in rat mesenteric resistance arteries. (A₁–C₁), data showing responses to cumulative administration of eucalyptol (100 µM–5 mM) on high-K⁺ (A₁) or U46619 (B₁) or phenylephrine (C₁) -induced contraction. (A₂–C₂), statistical analysis of the relaxation response to eucalyptol. (D₁), effect of L-NNA (500 µM) on the eucalyptol-induced vasodilation. (D₂), statistical analysis of the relaxation response to eucalyptol in the presence of L-NNA. Inset: representative trace showing responses to vehicle, tween 80 (0.0002–0.02%). Mean ± SD (n = 7). (W/O: wash out).