Biphasic effect of hydrogen peroxide on skeletal muscle arteriolar tone via activation of endothelial and smooth muscle signaling pathways

We hypothesized that hydrogen peroxide (H₂O₂) has a role in the local regulation of skeletal muscle blood flow, thus significantly affecting the myogenic tone of arterioles. In our study, we investigated the effects of exogenous H₂O₂ on the diameter of isolated, pressurized (at 80 mmHg) rat gracilis skeletal muscle arterioles (diameter of ∼150 μm). Lower concentrations of H₂O₂ (10 ⁶-3 × 10^-5 M) elicited constrictions, whereas higher concentrations of H₂O₂ (6 × 10^-5-3 × 10^-4 M), after initial constrictions, caused dilations of arterioles (at 10^-4 M H₂O₂, ∼19 ± 1% constriction and 66 ± 4% dilation). Endothelium removal reduced both constrictions (to -10 ± 1%) and dilations (to 33 ± 3%) due to H₂O₂. Constrictions due to H₂O₂ were completely abolished by indomethacin and the prostaglandin H ₂/thromboxane A₂ (PGH₂/TxA₂) receptor antagonist SQ-29548. Dilations due to H₂O₂ were significantly reduced by inhibition of nitric oxide synthase (to 38 ± 7%) but were unaffected by clotrimazole or sulfaphenazole (inhibitors of cytochiome P-450 enzymes), indomethacin, or SQ-29548. In endothelium-denuded arterioles, clotrimazole had no effect, whereas H₂O₂-induced dilations were significantly reduced by charybdotoxin plus apamin, inhibitors of Ca ²⁺-activated K⁺ channels (to 24 ± 3%), the selective blocker of ATP-sensitive K⁺ channels glybenclamide (to 14 ± 2%), and the nonselective K⁺-channel inhibitor tetrabutylammonium (to -1 ± 1%). Thus exogenous administration of H ₂O₂ elicits 1) release of PGH₂/TxA₂ from both endothelium and smooth muscle, 2) release of nitric oxide from the endothelium, and 3) activation of K⁺ channels, such as Ca ²⁺-activated and ATP-sensitive K⁺ channels in the smooth muscle resulting in biphasic changes of arteriolar diameter. Because H ₂O₂ at low micromolar concentrations activates several intrinsic mechanisms, we suggest that H₂O₂ contributes to the local regulation of skeletal muscle blood flow in various physiological and pathophysiological conditions.