RESUMEN
In the literature, the distribution of nitrite and nitrate, the major metabolites of nitric oxide (NO), between plasma and erythrocytes and its dependency on partial CO2 pressure (pCO2) in mammalian blood are uncertain. By means of a previously reported fully validated stable-isotope dilution gas chromatography-mass spectrometry (GC-MS) method, we measured nitrite and nitrate concentrations in heparinized plasma from venous, arterial and arterialized blood donated by five healthy non-exercising volunteers at three different time points (0, 15, 30 min). pCO2, pH and oxygen saturation were measured by standard techniques. The nitrite and nitrate concentrations and the nitrite-to-nitrate ratio in plasma did not correlate with pCO2 (r=-0.272, P=0.07). Nitrite was found to be almost evenly distributed between plasma and erythrocytes of another eleven healthy non-exercising subjects. In a rabbit model of ARDS, no differences were found in the plasma nitrite and nitrate concentrations comparing normoventilation with hypercapnia. Our studies suggest that the distribution of nitrite between plasma and erythrocytes at rest is largely even and independent of pCO2 in blood of healthy humans and rabbits with ARDS.