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

In 1990, McGown demonstrated in vitro a limitation of extracellular me themoglobin (metHb) formation by releasing and recycling of ascorbic a cid by red blood cells [1]. In order to investigate the autoxidation o f free or modified hemoglobin in plasma and the possibility of reprodu cing McGown's phenomenon in vivo, we performed a 50% blood mass exchan ge in guinea-pigs with a 70+/-5 g/l dex-BTC-Hb solution (metHb<5%). Me themoglobin was determined according to Evelyn-Malloy's method. We obs erved a clear but limited oxidation of plasmatic hemoglobin (MetHb sim ilar to 30-40% at t=12hrs up to t=24hrs). A similar blood mass exchang e was performed with the same hemoglobin solution which was previously totally oxidized into metHb. 40% of this methemoglobin was found to b e reduced after 12hrs. These results demonstrated a marked reducing ac tivity by residual blood as shown by others [2]. The addition of poten tially protective compounds such as ascorbic acid (non enzymatic intra erythrocytar reduction pathway), methylene blue or riboflavin (enzymat ic intraerythrocytar pathway), allowed a significant drop in the methe moglobin level. On the contrary, we didn't observe any reducing effect with reduced glutathione.