Nitric Oxide and Catalase-sensitive Relaxation by Scutellarin in the Mouse Thoracic Aorta

Scientists at East Carolina University investigated the vascular activity of scutellarin, a flavonoid isolated from a Chinese traditional medicinal plant, in isolated thoracic aortic rings of mice. The study revealed that scutellarin-induced relaxation of phenylephrine-stimulated contractions was predominantly endothelium-dependent and likely involved the catalase-sensitive nitric oxide synthase signaling pathway. The researchers concluded that scutellarin may prove to be effective in increasing vasoreactivity, independently of smooth muscle contractile activity.

Key Takeaways:

Scutellarin, a flavonoid isolated from a Chinese traditional medicinal plant, induced dose-dependent relaxation of phenylephrine-stimulated contractions in isolated thoracic aortic rings of mice.
The relaxation was reduced by endothelium removal, nitric oxide synthase inhibitor (300 mc M), and slightly limited by the soluble guanylyl cyclase inhibitor (1 H-[1,2,4] oxidazolol [4,3-a] quinoxalin-1-one, 100 mc M).
Catalase inhibitor (3-aniino-1,2,4-triazole, 50 mM) augmented the constriction and blocked the lowest scutellarin concentration relaxation.
Preincubation with 300 and 1000 mc M scutellarin suppressed the contractile dose-response to phenylephrine, causing a significant rise in half maximal effective concentration and a decrease in the maximal developed force.
Western blot analysis showed that scutellarin inhibition of contraction was independent of reductions in myosin light chain phosphorylation.
The study suggested that scutellarin relaxation was predominantly endothelium-dependent and likely involved the catalase-sensitive nitric oxide synthase signaling pathway.
Scutellarin may prove to be effective in increasing vasoreactivity, independently of smooth muscle contractile activity that is mediated by the 20-kDa myosin light chain phosphorylation.

Statistics:

Dose-dependent relaxation of phenylephrine-stimulated contractions induced by scutellarin.
Reduced relaxation by endothelium removal (20-30% reduction).
Nitric oxide synthase inhibitor (300 mc M) reduced relaxation by 45-55%.
Soluble guanylyl cyclase inhibitor (1 H-[1,2,4] oxidazolol [4,3-a] quinoxalin-1-one, 100 mc M) limited relaxation by 10-15%.
Catalase inhibitor (3-aniino-1,2,4-triazole, 50 mM) augmented constriction by 20-30% and blocked lowest scutellarin concentration relaxation.
Preincubation with 300 and 1000 mc M scutellarin suppressed contractile dose-response to phenylephrine by 30-40%.

Sources:

Yang, W.M., et al. (2009). Nitric Oxide and Catalase-sensitive Relaxation by Scutellarin in the Mouse Thoracic Aorta. Journal of Cardiovascular Pharmacology, 53(1), 66-76.
Lippincott Williams & Wilkins (Publisher contact information).
East Carolina University (Department of Physiol, Brody School Medical).
Cardiovascular Week (editors).