Measurement of plasma nitrite by chemiluminescence.

Studies have demonstrated that plasma nitrite ([Formula: see text]) reflects endothelial nitric oxide (NO) production. In addition, [Formula: see text] has been shown to have biological activities associated with its reduction to NO in blood and tissues. Therefore, determination of plasma [Formula: see text] has been proposed as a prognostic marker for cardiovascular diseases. Typical concentrations of [Formula: see text] in the plasma are in the nanomolar range and determination of this [Formula: see text] poses a challenge in terms of both sensitivity and specificity. Thus, a highly sensitive, chemiluminescence method that is based on the reduction of [Formula: see text] by potassium iodide and iodine is being used to determine the nitrite in biological fluids. This method has the sensitivity, but also measures other nitric oxide species such as S-nitrosothiols and N-nitrosamines. We, therefore, developed an alternative method based on the reduction of [Formula: see text] by ascorbic acid in strongly acidic media. As part of the methodology, glacial acetic acid and ascorbic acid are introduced into the purge vessel of the NO analyzer. Samples containing [Formula: see text] are injected into the purge vessel and the chemiluminescence signals generated as a result of the formation of NO are then measured. We find that under these conditions [Formula: see text] is stoichiometrically reduced to NO. Other traditional NO-generating species, such as S-nitrosothiols, N-nitrosamines, nitrated lipids, and nitrated proteins, did not interfere in the determination of plasma [Formula: see text]. Using the present method, plasma [Formula: see text] in fasting human subjects has been determined to be in the range of 56-210 nM (mean +/- SD = 110 +/- 36 nM; n = 8).