Reduced coronary NO production in conscious dogs after the development of alloxan-induced diabetes.

The role of nitric oxide (NO) in the control of coronary blood flow (CBF) during the development of diabetes is unknown. To study this, mongrel dogs were chronically instrumented using sterile techniques for measurements of systemic hemodynamics and CBF. With heart rate controlled (150 beats/min), veratrine (1-10 micrograms/kg) caused dose-dependent increases in CBF; e.g., 5 mirograms/kg of veratrine increased CBF by 57 +/- 7% from 41 +/- 1.3 ml/min (P < 0.05). The dogs developed diabetes 4-5 wk after injection of alloxan (40-60 mg/kg iv, blood glucose levels were 384 +/- 18 mg/dl). After diabetes the same doses of veratrine caused smaller increases in CBF; i.e., 5 micrograms/kg of veratrine increased CBF by 32 +/- 2% (P < 0.05 compared with control) from 28 +/- 4 ml/min. ACh- and adenosine-induced coronary vasodilation were reduced after diabetes as well. In anesthetized dogs after diabetes, vagal stimulation caused smaller increases in CBF. ACh and bradykinin caused smaller increases in NO(-)(2) production in coronary microvessels from diabetic dogs. Furthermore, despite the fact that mRNA for endothelial cell NO synthase from the aorta was increased twofold with the use of Northern blotting, the protein for aortic endothelial constitutive NO synthase was reduced by 66% after diabetes, as determined by Western blotting. Our results indicate that the NO-dependent coronary vasodilation by the Bezold-Jarisch reflex is impaired in conscious dogs after diabetes. The mechanism responsible for the impaired endothelium-dependent coronary vasodilation is most likely the decreased release of NO from the endothelium.