Acetylcholine-Induced Relaxation of Rabbit Basilar Artery In Vitro Is Rapidly Reduced by Reactive Oxygen Species in Acute Hyperglycemia

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Abstract
We examined the effects of acute hyperglycemia on the function of rabbit cerebral arteries in vitro. It was hypothesized that increased formation of reactive oxygen species (ROS) could occur, which could explain how hyperglycemia aggravates certain pathologic situations such as cerebral ischemia. Three-millimeter basilar artery segments were incubated in either normoglycemic (NG, 5.5 mM D-glucose) or hyperglycemic (HG, 25 mM D-glucose) solution containing 3.10(-6) M indomethacin. After 90 minutes equilibration, a test (=T1) of relaxation to acetylcholine (Ach) at three concentrations was performed on histamine-precontracted segments. Three further identical tests were performed (T2-T4), after 30-minute rest periods. Ach responses in NG solution were stable, whereas those in HG solution, although greater at T1, fell progressively from one test to the next (P < 0.0001 versus NG), whereas nitroprusside responses did not change. In separate experiments, this time-dependent fall in Ach responses was significantly prevented by superoxide dismutase (SOD) plus catalase (P = 0.0003), but not by SOD alone. It was also significantly prevented by the NAD(P)H oxidase inhibitors diphenyleneiodonium (P = 0.020) and apocynin (P = 0.0179), but not by allopurinol (xanthine oxidase inhibitor). Control experiments with l-glucose ruled out a hyperosmotic or non-specific glucose effect. We conclude that, in HG solution in vitro, rapidly increasing ROS production largely derived from NAD(P)H oxidase reduced relaxation to acetylcholine. The rapidity of this effect suggests that the function of these arteries may be affected during brief periods of hyperglycemia in vivo.