Experience with the particulate prostaglandin endoperoxide synthase assay for testing non-steroidal antiinflammatory drugs.

A microsomal prostaglandin endoperoxide synthase preparation was obtained from sheep vesicular glands and used as a test system for non-steroidal antiinflammatory drugs. The activity was measured oxygraphically with arachidonic acid as substrate. The assay conditions were optimized with respect to the concentrations of enzyme, substrate and hydroperoxidase co-substrate as well as preincubation. The validity of the test was assessed by eight known prostaglandin H synthase inhibitors and two antiinflammatory drugs not acting on this enzyme. Sodium diclofenac proved to be the most potent inhibitor. As shown with indometacin as example the test shows a good reproducibility. The data were fitted to a kinetic mathematical model assuming two distinct inhibitor binding sites with different affinities. This model gave in most cases a good fitting of the experimental data.