Interleukin-1 stimulation of phospholipase activity in rat synovial fibroblasts

Tritiated arachidonic acid (3H-AA)—labeled rat synovial fibroblasts stimulated with human recombinant interleukin-1β (rIL-1β) released incorporated radiolabel in a time-dependent and dose-dependent manner, with labeled prostaglandins representing 29% of the released radiolabel. Treatment of the cells with dibutyryl cAMP or prostaglandin E2 enhanced both spontaneous and rIL-1β-induced 3H-AA release; treatment with indomethacin or naproxen inhibited the response. The effects of these cyclooxygenase inhibitors on 3H-AA release were not reversed by the addition of prostaglandin E2. The activities of phospholipase A, phospholipase C, and diglyceride lipase were detected in the homogenates of rat synovial fibroblasts. Pretreatment of synovial cells with rIL-1β resulted in a threefold stimulation of phospholipase A activity and a slight increase in phospholipase C activity in cell homogenates. These data show that rIL-1β stimulates phospholipase activities in rat synovial fibroblasts and that at least one of these activities may be regulated by either prostaglandins or cAMP.