Plasma nitrate clearance in mice: modeling of the systemic production of nitrate following the induction of nitric oxide synthesis.

Nitric oxide (NO) is produced in mammals by the enzyme NO synthase (NOS) in response to a number of agents, including the experimental antitumour agent flavone acetic acid (FAA) and the cytokine tumour necrosis factor-alpha (TNF). NO is converted rapidly in the presence of oxygen, water and haemoglobin to oxidation products, largely nitrate. To quantitate the production of nitric oxide it is necessary to know the clearance of nitrate. The concentration of nitrite and nitrate ion in the plasma of C3H and BDF1 (C57BL6 x DBA2) mice was assessed before and after injection of sodium nitrate and sodium nitrite. Nitrite was covered rapidly to nitrate and the kinetics of elimination of nitrate were determined. There was no significant difference between results obtained with different mouse strains, between levels of nitrite and nitrate, or between i.p. and i.v. administration, and the observations were therefore combined. The volume of distribution of nitrate was 0.71 +/- 0.04 l/kg and the clearance was 0.32 +/- 0.02 l/h-1/kg-1 (plasma half-life, 1.54 h). Using previously published data, we developed a pharmacokinetic-pharmacodynamic model that relates the production of TNF in response to administration of FAA, the enhancement of NOS activity in response to TNF, and the elevation of plasma nitrate in response to NO production. This information permits the prediction from observed plasma nitrate values of the amount of NOS induced in vivo.