Inhibition of acetylcholine-induced EDHF response by elevated glucose in rat mesenteric artery

The effects of high glucose on endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxations of isolated rat mesenteric artery and the possible involvement of reactive oxygen species in these responses were investigated. After precontraction with phenylephrine (3 × 10− 8-10− 7 M), acetylcholine (10− 8-3 × 10− 6 M) and A 23187 (10− 8-3 × 10− 6 M), a calcium ionophore, induced concentration-dependent relaxations in the presence of NW-nitro-l-arginine methyl ester (L-NAME) (10− 4 M) and indomethacin (10− 5 M). These relaxations were abolished in the presence of charybdotoxin (2 × 10− 7 M) plus apamin (10− 7 M) and were assumed to be mediated by EDHF. Effects of elevated glucose were examined by incubating the arterial rings for 6 h in Krebs-Henseleit solution containing 22.2 mM glucose. Under these conditions relaxation to acetylcholine was significantly attenuated but was unchanged when the tissues were incubated for 6 h in solution containing 11.1 mM mannitol used as hyperosmotic control. Addition of superoxide dismutase (SOD) (75 U/ml) and combination of SOD with catalase (200 U/ml) during incubation with high glucose significantly preserved the impairment of EDHF-mediated relaxations to acetylcholine. A 23187-induced endothelium-dependent relaxation was not affected by high glucose. Similarly, relaxations to pinacidil (10− 10-10− 5 M) and to sodium nitroprusside (SNP) (10− 10-3 × 10− 7 M) were also unchanged in the rings exposed to high glucose. These results suggest that in rat mesenteric arteries exposed to elevated glucose receptor-dependent EDHF-mediated relaxations (acetylcholine-induced) are impaired whereas receptor-independent ones (A 23187-induced) and responses to smooth muscle relaxants that exert their effects through mechanisms independent of endothelium are unaffected. Our findings lead us to propose that reactive oxygen species like superoxide (·O2−) and hydrogen peroxide (H2O2) do seem to play a role in the impairment of EDHF-mediated relaxations in the presence of elevated glucose.