Background: Plasma nitrite/nitrate (NOx) is a stable end product of the vasodilator nitric oxide (NO). However, there are few reports about plasma NOx levels in humans.
Hypothesis: The purpose of this study was to assess the availability of plasma NOx for evaluating basal endogenously-synthesized or endothelium-derived NO, and to examine whether NOx levels are lowered in patients with coronary artery disease (CAD) or its risk factors.
Methods: Plasma NOx levels were measured using an automated system based on the Griess reaction. NOx levels for a 24-h period reproducibly became lowest at 6 A.M. in restricted healthy volunteers, and became stable in inpatient volunteers at 6 A.M. within 4 days after admission.
Results: Based on these findings, NOx levels at 6 A.M. in inpatients can be considered as the basal levels. In 40 inpatients suspected of CAD (28 men, 12 women; mean age 60 +/- 11 years), the basal levels of NOx were not related to CAD and its risk factors, except for hypercholesterolemia. The NOx level of patients with hypercholesterolemia was significantly lower than that of patients with normal cholesterol (n = 16,34 +/- 16 mumol/l vs. n = 24, 49 +/- 23 mumol/l, p < 0.03). Furthermore, the NOx levels correlated negatively with the total cholesterol and low-density lipoprotein cholesterol levels (r = -0.40, p < 0.01; r = -0.47, p < 0.003, respectively), but not with other lipid fraction levels.
Conclusion: The results suggest that the quantity of basal endothelium-derived NO synthesis may be decreased in the presence of hypercholesterolemia.