Inhibition of prostaglandin synthesizing enzymes by haptoglobin and plasma of rats with inflammation.

Administration of carrageenin or adjuvant to rats to induce inflammation produced increases in the plasma haptoglobin level. Simultaneously, there was an increase in the activity of the plasma inhibitor of prostaglandin E2 synthesis. Partially purified haptoglobin inhibited the microsomal over-all conversion of arachidonic acid to prostaglandin E2. The addition of the haptoglobin inhibited two heme-dependent reactions catalyzed by a purified enzyme of seminal vesicle microsome, i.e., the prostaglandin G2 synthesis from arachidonic acid and the conversion of prostaglandin G2 to H2. However, the plasma inhibitory activity was accounted for only partially by the haptoglobin contained in the plasma from treated rats.