H2O2 is an endothelium-derived relaxing factor in the cerebral artery of the mouse

Annick Drouin & Éric Thorin. Montreal Heart Institute, Faculty of Medicine, Department of Surgery, Montreal, Quebec, H1T 1C8, Canada.

Hydrogen peroxide (H2O2) induces relaxation of cerebral arteries ( Rosenblum, 1987). More recently, H2O2 has been referred to as an endothelium-derived hyperpolarising factor in mice ( Matoba et al., 2000). Others suggest that H2O2 induces relaxation via activation of the cAMP pathway ( Iida & Katusic, 2000). The purpose of the present study was to characterise the dilatory mechanism of action of endothelium-derived H2O2 in the mouse cerebral artery.

Posterior cerebral arteries (average diameter of 110 m m) were isolated from 12±2 week-old C57Bl/6 male mice (29±1g) and pressurized at 60 mm Hg in an arteriograph (Vequaud & Thorin, 2001). Endothelium-dependent dilatation to acetylcholine (ACh, 0.1nM to 30 µM) or to exogenous H2O2 (0.1nM to 30 µM) were obtained in vessels pre-constricted with phenylephrine (30 µM). Results are reported in percentage of the maximal diameter obtained in zero Ca2+. Data are reported as mean±sem of n= 6.

In the presence of catalase (100 U/ml), ACh-induced maximal dilatation was reduced (P<0.05) from 45±6% to 15±2%. N-nitro-L-arginine (L-NNA, 10 µM), a NOS inhibitor, likewise reduced ACh-dependent dilatation to 24±3% (P<0.05). Combination of catalase and L-NNA, however, had no additive inhibitory effects, leading to a maximal dilatation to ACh of 16±1%. The endothelial NOS is known to generate O 2 - in the absence of tetrahydrobiopterin (BH 4; Vasquez-Vivar et al., 1998), with superoxide dismutase generating H2O2. In the presence of catalase, BH 4 (1 mM) restored (P<0.05) the maximal dilatation induced by ACh (36±1%). Exogenous H2O2 induced a similar maximal dilatation with or without the endothelium (28±2 % and 23±2% respectively). This response was prevented (P<0.05) by catalase (3±1%) or ODQ (10 µM, 3±1%), an inhibitor of soluble guanylate cyclase.

In conclusion, ACh induces a dilatation of the cerebral artery of the mouse partly by stimulating the release of endothelium-derived H2O2. H2O2 apparently originates from the activity of the NOS in absence of BH4 and activates the smooth muscle guanylate cyclase to produce the dilatation. These results suggest that in normal conditions, H2O2 is an endothelium-derived relaxing factor in mouse cerebral arteries.

Iida & Katusic (2000). Stroke. 31, 2224-2230.
Matoba et al. (2000). J. Clin. Invest. 106, 1521-1530.
Rosenblum (1987). Circ. Res. 61 , 601-603.
Vasquez-Vivar et al. (1998). Proc. Natl. Acad. Sci. USA. 95, 9220-9225.
Vequaud & Thorin (2001). Circ. Res. 89 , 716-722.