Role of inosine in prevention of methaemoglobinaemia in the pig: in vitro studies.

Methaemoglobin reductase activity was studied in pig, human and cattle erythrocytes incubated in a medium containing glucose or inosine as NADH generator. With glucose, methaemoglobin reduction was very fast in human, less so in cattle and slowest in pig erythrocytes. With inosine, pig red cells reduced methaemoglobin more rapidly than human red cells and in bovine erythrocytes the enzyme activity was undetectable. In intact red cells the ability to reduce methaemoglobin depends on the amount of NADH the cell can produce with glucose or inosine utilization. The results show that pig red blood cells utilize inosine as the NADH generator for enzymatic reduction of methaemoglobin. The greater efficiency of pig red cells could be due to several factors: better inosine transport, more active metabolic pathway for inosine utilization (so that more NADH is produced), or greater MR activity when NADH is in excess. In any case, the high rate of methaemoglobin reduction could explain the lower prevalence of methaemoglobinaemia in pigs than in cattle.