Catalase has negligible inhibitory effects on endothelium‐dependent relaxations in mouse isolated aorta and small mesenteric artery

The current study examined the hypothesis that endothelial production of hydrogen peroxide (H 2 O 2 ) mediates relaxations to acetylcholine (ACh) in aorta and small mesenteric arteries (SMA) from mice. Relaxations to ACh (0.01–10 μ M ) and H 2 O 2 (0.1–1000 μ M ) were produced in aorta and SMA isolated from wild‐type C57BL/6 mice and type II diabetic mice (db/db). In SMA, relaxations to ACh were produced in the presence of N ω ‐nitro‐ L ‐arginine methyl ester ( 100 μ M ) and indomethacin (Indo, 10 μ M ). 1‐H[1,2,4]oxadiazolo[4,3‐]quinoxalin‐1‐one (10 μ M ) significantly reduced ACh‐induced relaxations in SMA, abolished responses in aorta, but had no effect on relaxations induced by H 2 O 2 . Catalase (2500 U ml −1 ) abolished responses to H 2 O 2 , but did not alter relaxations to ACh in the SMA and only caused a small rightward shift in responses to ACh in the aorta. ACh‐, but not H 2 O 2 ‐, mediated relaxations were significantly reduced by tetraethylammonium (10 m M ), the combination of apamin (1 μ M ) and charybdotoxin (100 n M ), and 25 m M potassium chloride (KCl). Higher KCl (60 m M ) abolished relaxations to both ACh and H 2 O 2 . Polyethylene glycolated superoxide dismutase (100 U ml −1 ), the catalase inhibitor 3‐amino‐1,2,4‐triazole (3‐AT, 50 m M ) and treatment with the copper chelator diethyldithiolcarbamate (3 m M ) did not affect relaxations to ACh. H 2 O 2 ‐induced relaxations were endothelium‐independent and were not affected by ethylene diamine tetraacetic acid (EDTA 0.067 m M ), 4‐aminopyridine (1 m M ), ouabain (100 μ M ) and barium (30 μ M ), 3‐AT or Indo. Although the data from this study show that H 2 O 2 dilates vessels, they do not support the notion that H 2 O 2 mediates endothelium‐dependent relaxations to ACh in either aorta or SMA from mice.British Journal of Pharmacology (2003) 140 , 1193–1200. doi: 10.1038/sj.bjp.0705549