[Superoxide anion inhibit endothelium-dependent relaxation in rat mesenteric artery]

To explore the resistant arterial effect of superoxide anion and its possible mechanisms.

The third branch of the superior mesenteric artery in male Sprague-Dawley (200-300 g) rats was rapidly excised. Periadventitial fats and connective tissues were removed and the artery was dissected into about 2 mm rings. Each ring was dispensed between two stainless steel wires (diameter 0.0394 mm) in a 5 ml organ bath (DMT 610 M, Danish Myo Technology, Denmark). Isometric force recording studies in vitro of rat mesenteric arterial rings were recorded by Powerlab Syetem. Exposure of arteries to superoxide was accomplished through the auto-oxidation of pyrogallol added to the artery baths. Then endothelium-dependent or independent relaxation was investigated, respectively.

Exposure to pyrogallol (10, 100, 300, and 1 000 micromol/L) which could produce superoxide anion for 15 min resulted in a dose-dependent manner in a decrease of acetylcholine(ACh)-induced relaxation in rat mesenteric artery. Especially, the two predominant components of acetylcholine(ACh)-induced endothelium-dependent relaxation, EDHF component and NO component were both inhibited by superoxide anion from pyrogallol. However, exposure to superoxide anion from pyrogallol had no effect on the endothelium-independent relaxations to pinacidil or sodium nitroprusside (SNP) in rat mesenteric artery.

These results indicate that superoxide anion can inhibit the endothelium-dependent relaxation in rat mesenteric artery, but has no effect on the endothelium-independent relaxation, in which the inhibited effect of EDHF and NO from endothelium is involved.