Basal nitric oxide production is not reduced in patients with noninsulin-dependent diabetes mellitus

Vascular disease is the leading cause of morbidity, disability and death in patients with noninsulin-dependent diabetes mellitus. Abnormalities in endothelium-derived nitric oxide (NO) have been demonstrated to be involved in the pathogenesis of vascular disease. By measuring hemodynamic responses to a NO synthase agonist or antagonist, previous studies have shown the presence of NO deficiency in patients with noninsulin-dependent diabetes mellitus, a method of assessing bioactive NO formation. However, direct biochemical evidence that this is the case, has not been produced. In vivo NO is metabolized into nitrate, an end breakdown product of NO, which can be used as an index of endogenous NO formation. To investigate further whether decreased basal synthesis of NO may be a major cause of endothelium-mediated vascular dysfunction in patients with noninsulin-dependent diabetes mellitus, the plasma nitrite/nitrate levels of 15 patients were examined and compared with 13 normal controls. The results showed that in basal conditions plasma nitrite/nitrate levels were not reduced in diabetic patients compared with normal controls (37.3 +/- 14.7 versus 29.4 +/- 8.6 mumol/l). It was concluded that in noninsulin-dependent diabetes mellitus patients, endothelium-derived basal NO formation is not impaired. This study, taken with previous observations, suggests that factors other than diminished basal NO production, such as reduced bioavailability of NO probably due to the augmented production of superoxide anion with subsequently increased inactivation of NO, contribute to the high incidence of vascular disease in patients with noninsulin-dependent diabetes mellitus.