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

• Published in: Life sciences (1973) 2005-11, Vol.78 (1), p.14-21
• Main Authors: Özkan, Melike Hacer, Uma, Serdar
• Format: Article
• Language: English
• Subjects: Acetylcholine - antagonists & inhibitors; Acetylcholine - pharmacology; Animals; Biological Factors - biosynthesis; Blood Glucose - physiology; Calcimycin - pharmacology; Elevated glucose; Endothelium, Vascular - drug effects; Endothelium, Vascular - physiology; Endothelium-derived hyperpolarizing factor; Free Radical Scavengers - pharmacology; In Vitro Techniques; Ionophores - pharmacology; Male; Mesenteric Arteries - drug effects; Mesenteric Arteries - metabolism; Muscle Contraction - drug effects; Muscle Relaxation - drug effects; Muscle Relaxation - physiology; Muscle, Smooth, Vascular - drug effects; Nitric Oxide - physiology; Phenylephrine - pharmacology; Rat mesenteric artery; Rats; Rats, Wistar; Reactive oxygen species; Reactive Oxygen Species - metabolism; Superoxide Dismutase - pharmacology; Vasoconstrictor Agents - pharmacology
• ISSN: 0024-3205; 1879-0631
• DOI: 10.1016/j.lfs.2005.02.036

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 N W-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 (·O 2 −) and hydrogen peroxide (H 2O 2) do seem to play a role in the impairment of EDHF-mediated relaxations in the presence of elevated glucose.