Substantial evidence exists that diabetes results in impaired endothelial dysfunction suggesting diminished nitric oxide production from diabetic endothelium. It is not known what factors contribute to the development of this defect. In this study, we tested whether chronic treatment in vivo with NOX-101, a water-soluble nitric oxide scavenger, prevents endothelial dysfunction in diabetes. Sprague-Dawley rats were made diabetic by an intravenous injection of streptozotocin. A subgroup of control or diabetic animals received twice daily subcutaneous injections of 80 mg/kg NOX-101 beginning at 48 h after streptozotocin was injected and throughout 8 weeks of diabetes. Body weights and glucose concentrations were monitored weekly. At the end of 8 weeks, blood glucose and glycosylated haemoglobin was raised in diabetic rats but serum insulin concentrations were reduced. Treatment with NOX-101 did not alter glucose or insulin concentrations in control or diabetic rats; however, total glycosylated haemoglobin was partially reduced compared with untreated rats. In a subgroup of 2-week diabetic and age-matched rats fasted for 24 h, NOX-101 abolished total urinary nitrate plus nitrite (an index of nitric oxide production in vivo). In isolated tissue baths, relaxation to the endothelium-dependent vasodilator, acetylcholine, was impaired in diabetic aortic rings and relaxation to nitroglycerin was unaltered. Treatment of control rats with NOX-101 did not alter maximum relaxation to acetylcholine but shifted the response curve slightly to the right. In contrast in diabetic rats, NOX-101 prevented the impairment in endothelium-dependent relaxation but had no effect on relaxation induced by nitroglycerin. These data suggest the possibility that diabetes-induced endothelial dysfunction in diabetes results, in part, from a paradoxical increase in nitric oxide production during the course of the disease. This suggests a novel pathway of vascular complications.
