Vasorelaxant Effect of Trachelospermi caulis Extract on Rat Mesenteric Resistance Arteries

Abstract

Background: Trachelospermi caulis (T. caulis) has been used as a traditional herbal medicine in Asian countries. Although it is well known that T. caulis has beneficial effects, no sufficient research data are available on the cardiovascular effect of T. caulis. We investigated whether T. caulis extract has vascular effects in rat resistance arteries in this study.

Methods: To examine whether T. caulis extract affects vascular reactivity, we measured isometric tension of rat mesenteric resistance arteries using a multi-wire myograph system. T. caulis extract was administered after arteries were pre-contracted with high K⁺ (70 mM) or phenylephrine (5 µM). Vanillin, a single active component of T. caulis, was used to treat mesenteric arteries.

Results: T. caulis extract caused vascular relaxation in a concentration-dependent manner, which was endothelium-independent. To further identify the mechanism, we incubated the arteries in Ca²⁺-free solution containing high K⁺, followed by a cumulative administration of CaCl₂ (0.01-2.0 mM) with or without T. caulis extract (250 µg/mL). The treatment of T. caulis extract decreased contractile responses induced by the addition of Ca²⁺, which suggested that the extracellular Ca²⁺ influx was inhibited by the T. caulis extract. Moreover, an active compound of T. caulis extract, vanillin, also induced vasodilation in mesenteric resistance arteries.

Conclusion: T. caulis extract and its active compound, vanillin, concentration-dependently induced vascular relaxation in mesenteric resistance arteries. These results suggest that the administration of T. caulis extract could help decrease blood pressure.

Keywords: Ca2+; Trachelospermi caulis; mesenteric resistance arteries; relaxation; vanillin; vasodilation.

Figure 1

T. caulis extract-induced vasodilation in rat mesenteric arteries. (A,B) Representative traces showing responses to cumulative administration of T. caulis extract (5–250 μg/mL) on high K⁺ (A) or phenylephrine (B)-induced contraction endothelium intact arteries. (C) Representative traces showing responses to cumulative administration of T. caulis extract (5–250 μg/mL) on phenylephrine-induced contraction in endothelium denuded arteries. (D) Statistical analysis of the relaxation response to T. caulis extract. Mean ± SD (n = 7). Endo + means endothelium-intact arteries and Endo − means endothelium-denuded arteries. * p < 0.05 and ** p < 0.005 for KCl (Endo +) versus PE (Endo −); ## p < 0.005 and ### p < 0.001 for PE (Endo +) versus PE (Endo −). Inset, representative trace showing responses to vehicle, DMSO (0.0025–0.125%). (W/O: wash out; TC: T. caulis extract; PE: phenylephrine).

Figure 2

T. caulis extract induced endothelium-independent vasodilation in rat mesenteric resistance arteries. (A) Representative trace showing T. caulis extract-induced vasodilation in the endothelium-intact mesenteric arteries. (B) Representative trace showing T. caulis extract-induced vasodilation in the endothelium-denuded mesenteric arteries. (C) Statistical analysis of T. caulis-induced vasodilation. Mean ± SD (n = 5). (ACh: acetylcholine; W/O: wash out; TC: T. caulis extract).

Figure 3

Effect of L-NNA, indomethacin and ODQ on T. caulis-induced vasodilation. (A–C) Representative trace showing T. caulis extract-induced vasodilation in the presence of L-NNA (A), ODQ (B) and indomethacin (C). (D) Statistical analysis of the relaxation response of T. caulis extract in the presence of L-NNA, ODQ and indomethacin. Relaxation of arteries is expressed as the percentage of the contraction induced by PE (5 μΜ). Mean ± SD (n = 5). (TC: T. caulis extract; L-NNA: Nω-Nitro-L-arginine; ODQ: 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one; W/O: wash out).

Figure 4

Effect of K⁺ channel blockers on T. caulis extract-induced vasodilation. (A–D) Effects of T. caulis extract in the mesenteric arteries pre-contracted with PE (5 μΜ) in the presence of TEA (A), BaCl₂ (B), 4-AP (C) or glibenclamide (D). (E) Statistical analysis of the relaxation response of T. caulis extract in the presence of K⁺ blockers. Relaxation of arteries is expressed as the percentage of the contraction induced by PE (5 μΜ). Mean ± SD (n = 7). (TC: T. caulis extract; TEA: tetraethylammoni-um; Gli: glibenclamide; 4-AP: 4-aminopyridine; W/O: wash out).

Figure 5

T. caulis extract inhibited extracellular Ca²⁺-induced vasoconstriction. (A,C) Representative traces showing the contraction responses by repeated addition of Ca²⁺ are not changed in endothelium-intact (A) and endothelium-denuded (C) arteries. (B,D) Representative traces showing the effect of T. caulis in the mesenteric arteries treated with cumulative addition of CaCl₂ (0.1–2.0 mM) in endothelium-intact (B) and endothelium-denuded (D) arteries. (E) Statistical analysis of contraction induced by CaCl₂ in the mesenteric arteries with or without T. caulis. Mean ± SD (n = 7). *** p < 0.001 and **** p < 0.0001 for control (Endo +) versus TC (Endo +); ### p < 0.001 and #### p < 0.0001 for control (Endo −) versus TC (Endo −); † p < 0.05 for control (Endo +) versus control (Endo −); $ p < 0.05, $$ p < 0.01, and $$$ p < 0.001 for TC (Endo +) versus TC (Endo −). Endo + means endothelium-intact arteries and Endo − means endothelium-denuded arteries. (W/O: wash out; TC: T. caulis extract).

Figure 6

T. caulis extract reduced contraction induced by L-type voltage-gated calcium channel activation. (A) Representative trace showing the contraction response was not changed by treatment of vehicle (DMSO). (B) Representative trace showing the effect of T. caulis on the mesenteric arteries pre-constricted by BAY K8644. (C) Statistical analysis of relaxation induced by TC extract in the mesenteric arteries pre-constricted by BAY K8644. Mean ± SD (n = 7). ** p < 0.01, *** p < 0.001, and **** p < 0.0001 for DMSO versus TC (W/O: wash out; TC: T. caulis extract).

Figure 7

Vanillin-induced vasodilation in rat mesenteric resistance arteries. (A,B) Representative traces showing responses to cumulative administration of vanillin (0.01–20 mM) on high-K⁺ (A) or PE (B)-induced contraction. (C) Statistical analysis of the relaxation response to vanillin. Mean ± SD (n = 7). * p < 0.05 and **** p < 0.0001 for KCl versus PE (W/O: wash out).