The involvement of hydrogen peroxide in vasorelaxation to oleoylethanolamide in rat mesenteric arteries

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

We have shown that vasorelaxation to hydrogen peroxide (H2O2) is endothelium-dependent, and in first order mesenteric arteries (G1) is primarily nitric oxide-mediated. It also appears to be involved in EDHF-type responses, either directly or indirectly, in third order mesenteric arteries (G3) (Wheal et al., 2010b). Furthermore, we have reported a role for the endothelium in vasorelaxation to the endocannabinoid-like molecule N-oleoylethanolamide (OEA) (Wheal et al., 2010a). Therefore, the aim of this study was to examine the involvement of H2O2 in vasorelaxant responses to OEA and the endocannabinoid anandamide in rat mesenteric arteries.

Mesenteric arterial beds were taken from male, Wistar rats (250 – 360g). First (G1) and third (G3) order branches from the superior mesenteric artery were dissected free of adherent tissue, then placed onto wires in a myograph and all subjected to 9.81 mN of tension and left to equilibrate in warmed, gassed Krebs’-Henseleit buffer. Vessel tone was raised with methoxamine, and concentration-response curves to OEA or anandamide were conducted in the absence and presence of the nitric oxide synthase inhibitor, L-NAME (300μM), and catalase (1000 U/ml), which were added 30 minutes before experimentation.

OEA relaxed G1 mesenteric arteries in a concentration-dependent manner which was unaffected by catalase (pEC50% OEA Control = 6.95 ± 0.67, n = 6; Catalase-treated = 7.57 ± 0.66, n = 6; mean ± s.e.mean). However in G3 vessels, catalase inhibited vasorelaxation (P<0.05, two-way ANOVA vs. Controls, pEC50% OEA Control = 7.10 ± 0.55, n = 7; Catalase-treated = 5.52 ± 0.36, n = 6). Combined treatment with L-NAME further reduced this response (pEC50 Catalase + L-NAME = 4.27 ± 0.08, n = 4, P<0.05, two-way ANOVA vs. Catalase-treated group). The combination of catalase + L-NAME was not used in G1 vessels.

In summary, H2O2 is partly responsible for the vasorelaxant actions of OEA and anandamide, but only in smaller rat mesenteric arteries. This involvement is only uncovered following inhibition of nitric oxide synthesis.

Wheal et al. (2010a). Brit J Pharmacol. 160: 701-711.

Wheal et al. (2010b). BPS winter meeting poster presentation.

This work was funded by the British Heart Foundation.