Vasorelaxant effect of monoterpene carvacrol on isolated human umbilical artery

Carvacrol (CRV) is the main compound of essential oils extracted primarily from Thymus and Origanum species. Its various biological activities were confirmed: antioxidant, anti-inflammatory, antibacterial, antifungal, anti-tumour, antinematodal, and vasorelaxant action. Although vasodilation mediated by CRV was previously described, the exact mechanism of its action has not yet been established. Hence, the aim of this study was to investigate CRV vasoactivity on human umbilical arteries (HUA) and the different pathways involved in its mechanism of action using the tissue bath methodology. CRV caused a significant decrease in vascular tension of 5-HT-pre-contracted umbilical arteries, with EC₅₀ of 442.13 ± 33.8 µmol/L (mean ± standard error of the mean-SEM). At 300 µmol/L, CRV shifted downward the 5-HT concentration-response curve with a statistical significance of p < 0.001 obtained for the four highest concentrations. At a concentration of 1 mmol/L, CRV completely abolished BaCl₂-induced contraction in Ca²⁺-free Krebs-Ringer bicarbonate solution and the BAY K 8644-induced contraction in Krebs-Ringer bicarbonate solution (p < 0.001). Isopentenyl pyrophosphate, the antagonist of TRPV₃ channel, was able to decrease the efficacy of CRV (p < 0.001). The blocking of L-type Ca²⁺ channels on smooth muscle cells is the most probable mechanism of CRV-induced vasorelaxation. However, the role of TRPV₃ channels in CRV-induced vasodilation of HUA cannot be excluded either.