Studies on Lipid Metabolism in Articular Cartilage III. Prostaglandin Production and Its Origin in Articular Chondrocytes

Rabbit articular chondrocytes prelabeled with both 〔3H〕 arachidonate and 〔14C〕 stearate were used to characterize prostaglandin production and its origin when they were stimulated by Ca ionophore A23187 or bradykinin. The time course of the radioactivity release into the medium and intracellular lipid changes were followed. When the articular chondrocytes were incubated with both stimulants, the release of 〔3H〕 radioactivity into the medium increased up to 60 minutes amounting to about 10% of the total incorporated 〔3H〕 for A23187 and about 6% for bradykinin, respectively. During this time, very little 〔14C〕 labeled material was released into the medium. About 95% of the 〔3H〕 radioactivity released was arachidonate. However, prostaglandin E2 was found to be distinctly produced by both forms of stimulation. Small amounts of 6-keto-prostaglandin F1α appeared to be produced by the A23187 stimulation. Concomitant to the 〔3H〕 radioactivity release into the medium, significant 〔3H〕 loss from phosphatidylcholine (PC) from the cells was also found, but no significant change of 〔3H〕 was observed in other phospholipids, diacylglycerol and triacylglycerol of the cells. Since 〔3H〕 radioactivity was predominantly located in the 2-position of PC, the 〔3H〕 arachidonate might have been released from the 2-position of PC by the action of phospholipase A2 which was probably activated by the stimulation of A23187 or bradykinin. There was no significant change in the breakdown of PC between 16:0/20:4 and 18:0/20:4 species