Contribution of hydrogen peroxide to vasorelaxation in rat mesenteric arteries

Amanda Wheal, Stephen Alexander, Michael Randall. School of Biomedical Sciences, University of Nottingham, Nottingham, NG7 2UH, United Kingdom.

In recent years there has been much interest in the vascular actions of hydrogen peroxide (H2O2), and its potential role in endothelium-derived hyperpolarising factor-type (EDHF) relaxations (Shimokawa, 2010), either as an EDHF or through its potentiation (Edwards et al., 2008). The aim of this study was to investigate the mechanism of action of this reactive oxygen species and its involvement in EDHF-type responses in large and small rat mesenteric arteries.

Mesenteric arterial beds taken from male, Wistar rats (250 – 360g) were bathed in Krebs’-Henseleit buffer. First (G1) and third (G3) order branches from the superior mesenteric artery were then cleared of adipose and connective tissue, and were all mounted in a wire myograph at a basal tension of 9.81 mN (this tension leads to optimal methoxamine-induced tone). Once equilibrated, vessels were contracted with methoxamine, and concentration-response curves to the endothelium-dependent relaxant carbachol or H2O2 were conducted in the absence and presence of the nitric oxide synthase inhibitor, L-NAME (300μM), and catalase (1000 U/ml).

In G1 arteries, responses to carbachol were concentration-dependent and completely relaxed the tissue. Responses were inhibited by L-NAME (Control: pEC50 = 8.62 ± 0.39, Rmax = 110 ± 9%, n = 4; L-NAME: pEC50 = 6.55 ± 0.74, Rmax = 107 ± 19 %, n = 5; mean ± s.e.mean), but were not affected by catalase. In G3, responses to carbachol were unaffected by either L-NAME or catalase but the maximum relaxation (Control = 101 ± 3 %, n = 4; Combined treatment = 34 ± 4%, n = 5) was significantly reduced by their combination (one-way ANOVA, P < 0.0001). In G1, H2O2 caused relaxations which were sensitive to both L-NAME and removal of the endothelium, whilst in G3 the vasorelaxant responses were unaffected by L-NAME, but abolished by catalase..

In conclusion, H2O2 has a multi-factorial mechanism of action. Vasorelaxation to H2O2 is endothelium-dependent, and in G1 mesenteric arteries is primarily nitric oxide-mediated. It also appears to be involved in EDHF-type responses, either directly or indirectly, in smaller arteries.

Shimokawa, H (2010). Pflugers Arch - Eur J Physiol. 459: 915–922.

Edwards DH et al. (2008). Arterioscler Thromb Vasc Biol. 28: 1774-1781.

This work was funded by the British Heart Foundation.