High glucose impairs acetylcholine-mediated vasodilation in isolated arteries from Mourning doves (Z. macroura)

Normal avian plasma glucose levels are 1.5-2 times greater than mammals of similar size. In mammals, hyperglycemia induces oxidative stress and impaired endothelium-dependent vasodilation. Prior work has shown that mourning doves have high levels of antioxidants and isolated vessels have low endogenous oxidative stress. Therefore, the hypothesis was that endothelium-dependent vasodilation of isolated avian arteries would not be impaired following acute exposure to high glucose. Isolated small resistance cranial tibial arteries (c. tibial) were cannulated and pressurized in a vessel chamber then incubated with either normal or high glucose (20mM vs. 30mM) for 1h at 41°C. Vessels were then pre-constricted to 50% of resting inner diameter with phenylephrine (PE) followed by increasing doses of acetylcholine (ACh; 10(-9) to 10(-5)M, 5min per step). Percent vasodilation was measured by tracking the inner diameter with edge-detection software. Contrary to our hypothesis, ACh-induced vasodilation was impaired with acute exposure to high glucose (p=0.013). The impairment was not related to increased osmolarity since vasodilation of arteries exposed to an equimolar combination of 20mM d-glucose and 10mM l-glucose was not different from controls (p=0.273). Rather, the impaired vasodilation was attributed to oxidative stress since superoxide levels were elevated 168±42% (p=0.02) and pre-exposure of arteries to the superoxide dismutase mimetic tiron (10mM) improved vasodilation (p<0.05). Therefore, isolated arteries from doves do not have endogenous mechanisms to prevent impaired vasodilation resulting from high glucose-mediated increases in oxidative stress.