Relationship of thrombin‐stimulated arachidonic acid release and metabolism to mitogenesis and phosphatidylinositol synthesis

Thrombin and certain prostaglandins are both capable of stimulating the proliferation of cultured cells. Since thrombin stimulates the release and metabolism of arachidonic acid, the precursor of prostaglandins, we examined the relationship between this release and metabolism and the stimulation of cell division in cultured fibroblasts. We also examined the role of prostaglandin synthesis in thrombin‐stimulated phosphatidylinositol synthesis. The data in this report demonstrate that the release and metabolism of arachidonic acid are not necessary for thrombin‐stimulated cell division. The presence of a low concentration of chymotrypsin prevented thrombin‐stimulated arachidonic acid release and metabolism without affecting the stimulation of cell division. Furthermore, thrombin‐stimulated cell division occurred in the presence of indomethacin concentrations that prevented cyclooxygenase‐mediated metabolism of arachidonic acid. The following experiments showed that thrombin‐stimulated phosphati‐dylinositol synthesis was brought about by a cyclooxygenase‐mediated metabolite(s) of arachidonic acid. Indomethacin inhibited the cyclooxygenase‐mediated metabolism of arachidonic acid without affecting the thrombin‐stimulated release of arachidonic acid. Indomethacin also inhibited thrombin‐stimulated phosphatidylinositol synthesis. The dose dependence of this inhibition paralleled the inhibition by indomethacin of cyclooxygenase‐mediated metabolism of arachidonic acid. In addition, prostaglandin F₂, stimulated phosphatidylinositol synthesis in the presence of indomethacin concentrations which prevented thrombin‐stimulated phosphatidylinositol synthesis.