Extracellular superoxide dismutase in the vascular system of mammals

Plasma extracellular superoxide dismutase (EC-SOD) from the pig, cat, rabbit, guinea pig and mouse was found to be heterogeneous with regard to heparin affinity and could be separated into three fractions: A without affinity, B with weak affinity and C with relatively high affinity. Rat plasma EC-SOD was deviant and contained only A and B fractions. There were very large interspecies differences in total plasma EC-SOD activity and in division of the activity between the different fractions. Intravenous injection of heparin resulted in the pig, dog, cat, rabbit, guinea pig and mouse in a prompt increase in the plasma SOD activity. The increase was due to release of EC-SOD C to plasma, most probably from endothelial cell surfaces. In the rat, heparin induced no increase in plasma SOD activity, apparently because of the absence of EC-SOD C in this species. The relative heparin-induced increase in plasma EC-SOD C varied between 2 and 11 in the different species and was distinctly correlated with the heparin affinity of EC-SOD C in the particular species. Apparently the EC-SOD C, present in the vasculature, forms an equilibrium between plasma and endothelium, whereas EC-SOD A and B primarily exist in plasma. The wide diversity of EC-SOD in the vascular system of mammals with regard to total amount, division into fractions and distribution between plasma and endothelium indicates that the pathogenic potential of superoxide radicals in the extracellular space might vary much between species.