Abstract
Prostaglandin E2 (PGE2) production by rabbit synoviocytes was markedly stimulated by hydroxyapatite only after a 60‐minute delay. Release of 3H‐arachidonic acid (C20:4) and 3H‐PGE2 from cells with phospholipids that were prelabeled with 3H‐C20:4 did not occur in parallel. At 240 minutes, phospholipase activity in sonicated cell suspensions had increased only 38%, while cyclooxygenase activity had doubled (109%). This doubling, as well as the production of synoviocyte PGE2, was prevented by inhibiting the synthesis of protein. Cyclooxygenase is an inducible enzyme, and as such, it is a rate‐controlling step in PGE2 production.

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