Endothelium‐Independent Relaxation of Alkaloid Boldine in Isolated Aortas From Normotensive and Hypertensive Rats: Participation of Ca ²⁺ Channels

The regulation of vascular tone plays a fundamental role in blood pressure homeostasis and still represents a significant challenge in clinical practice. Boldine, a naturally occurring alkaloid from Peumus boldus, has emerged as a compound of interest due to its therapeutic potential. This study explored boldine's vasorelaxant effects on aortas of normotensive (NTR) and spontaneously hypertensive (SHR) rats. Nω-Nitro-l-arginine methyl ester (l-NAME) (a nitric oxide synthase inhibitor), ODQ (a soluble guanylate cyclase inhibitor), and tetraethylammonium (TEA) (a nonselective K⁺ channel blocker) exerted a modest inhibitory effect, causing a rightward shift in the boldine-induced relaxation curves without significantly affecting the maximal relaxation. Boldine affected both endoplasmic reticulum-based IP₃ and ryanodine receptors (RyRs) and transmembrane calcium channels in NTR aortas, whereas in SHR aortas, its actions were linked to IP₃ and RyRs receptors. These findings indicate that boldine's vasorelaxant effects may contribute to vascular tone regulation through modulation of Ca²⁺ channels.