Fig. 3.

Nitrite metabolism in fetal and adult whole blood and purified Hb. A: time course of disappearance of nitrite from maternal and fetal whole blood measured in vitro at 39°C after Hb concentrations; oxyHb saturations and pH are adjusted to be comparable. At time zero, 7.2 μmol of sodium nitrite are introduced to 10 ml blood. Nitrite disappears from fetal blood with an apparent half-time of 2.6 ± 0.9 min, significantly shorter than maternal blood, 6.7 ± 1.8 min (P < 0.001). B: more rapid initial increase in MetHb in fetal blood and a subsequently more rapid return to baseline dependent on high fetal MetHb reductase activity. C: time course of the disappearance of nitrite introduced into purified Hb solutions. The loss of nitrite is 1.9-fold faster in fetal Hb solutions than in maternal solutions.