The Tiger Milk Medicinal Mushroom TM02®, Lignosus rhinocerus (Agaricomycetes), Water-Soluble Sclerotial Extract (xLr®) Induces Vasorelaxation in Rat Isolated Aortae

<i>Lignosus rhinocerus</i> (Cooke) Ryvarden, a traditional medicinal mushroom in Southeast Asia, is utilized for various health conditions. Although there is evidence that <i>L. rhinocerus</i> sclerotia supplementation had decreased systolic blood pressure and improved acetylcholine-induced vasorelaxation, the underlying mechanism remains poorly understood. Therefore, this study investigated the vasorelaxant effect and possible mechanism of action of <i>L. rhinocerus</i> TM02^&#174; sclerotial cold water extract (xLr^&#174;) on rat-isolated aortae using an organ bath technique. Aortic rings removed from Sprague Dawley rats were pre-contracted with phenylephrine (PE) prior to the construction of the cumulative concentration-response curve to xLr^&#174;. Exposure to increasing concentrations of xLr^&#174; significantly relaxed the pre-contracted aorta &#91;maximum tissue contraction or relaxation response (<i>E</i>_max): 97.70 &#177; 5.21&#37;; <i>P</i> &#61; 0.0005&#93;. Furthermore, our findings revealed that the xLr^&#174;-induced vasorelaxation is independent of endothelium and muscarinic receptor-mediated pathways. The attenuation of PE-induced contractions by SKF96365 and nifedipine suggests the possible effect of xLr^&#174;-induced vasorelaxation on the inhibition of external calcium influx through membrane calcium channels. This is the first study detailing the endothelium-independent vasorelaxant effects of xLr^&#174; in isolated blood vessels. These findings have enhanced our understanding of the pharmacological effects of xLr^&#174; on vasculature.