REDUCTION OF NO-INDUCED METHEMOGLOBINEMIA REQUIRES EXTREMELY HIGH-DOSES OF ASCORBIC-ACID IN-VITRO

The objective of the present study was to investigate the treatment of nitric oxide (NO)-induced methemoglobinemia by ascorbate and its cons equences on red blood cell (RBC) glutathione in vitro. RBC were obtain ed from five healthy volunteers. The following experiments were carrie d out: (I) After methemoglobin generation by NO, ascorbate was added ( 2) RBC were simultaneously exposed to NO and ascorbate (3) Methemoglob in was generated by NO, ascorbate was added and incubation with NO con tinued. (1) After discontinuation of NO. the mean half life for methem oglobin was reduced from 195 min (controls) to 60 min (10 mM ascorbate ) in a dose-dependent manner. (2) Methemoglobin formation after 3 h of NO exposure was 2.7 +/- 0.3 % in controls and 1.8 +/- 0.1% with 10 mM ascorbate (p < 0.01). (3) Further methemoglobin formation was inhibit ed only by 10 mM ascorbate (p < 0.001). NO incubation did not affect R BC glulathione (86.5 +/- 19.6 and 86.5 +/- 19.6 mg/l, respectively). T reatment with 10 mM ascorbate significantly decreased glutathione (p < 0.002). In vitro, NO-induced methemoglobin formation is significantly decreased only by a high (10 mM) ascorbate concentration. Glutathione , critical for ascorbate activity, is not influenced by NO.