Hydroxyl-radical formation during prostaglandin formation catalysed by prostaglandin cyclo-oxygenase [proceedings].

The results indicate that haptoglobin may account for at least part of the inhibitor activity of plasma or serum. This seems to be consistent with the finding that administration of glucocorticoids in rats induced parallel changes in plasma inhibitor activity and haptoglobin concentration. However, no clear relationship between the haptoglobin concentration and the inhibitory actions of several vertebrate sera on the prostaglandin synthetase system could be demonstrated, except that the chicken and foetal calf sera with no haptoglobin were devoid of inhibitor activity. This might be explained by differences in the haptoglobin types of various sera, but other explanations are possible. The above results and our unpublished finding that the activity of the endogenous inhibitor of prostaglandin synthetase purified from Cohn IV-4 is associated with the haptoglobin fraction, together with the results of Deby et al. (1978), firmly support the view that haptoglobin might be the main protein that inhibits prostaglandin synthetase in uitro. This offers a new interpretation of the most characteristic and most important function of haptoglobin, the haemoglobin-binding capacity. Further investigation of this inhibitor activity of haptoglobin may lead to new results on haptoglobin-haemoglobin interactions.