METHEMOGLOBIN FORMATION AFTER ADMINISTRATION OF HEMOGLOBIN CONJUGATED TO CARBOXYLATE DEXTRAN IN GUINEA-PIGS - ATTEMPTS TO PREVENT THE OXIDATION OF HEMOGLOBIN

In 1990, McGown demonstrated in vitro a limitation of extracellular methemoglobin (metHb) formation by releasing and recycling of ascorbic acid by red blood cells [1]. In order to investigate the autoxidation of free or modified hemoglobin in plasma and the possibility of reproducing McGown's phenomenon in vivo, we performed a 50% blood mass exchange in guinea-pigs with a 70+/-5 g/l dex-BTC-Hb solution (metHb<5%). Methemoglobin was determined according to Evelyn-Malloy's method. We observed a clear but limited oxidation of plasmatic hemoglobin (MetHb similar to 30-40% at t=12hrs up to t=24hrs). A similar blood mass exchange was performed with the same hemoglobin solution which was previously totally oxidized into metHb. 40% of this methemoglobin was found to be reduced after 12hrs. These results demonstrated a marked reducing activity by residual blood as shown by others [2]. The addition of potentially protective compounds such as ascorbic acid (non enzymatic intraerythrocytar reduction pathway), methylene blue or riboflavin (enzymatic intraerythrocytar pathway), allowed a significant drop in the methemoglobin level. On the contrary, we didn't observe any reducing effect with reduced glutathione.