TUMOR-NECROSIS-FACTOR-ALPHA INCREASES RELEASE OF ARACHIDONATE AND PROLACTIN FROM RAT ANTERIOR-PITUITARY-CELLS

We investigated the effect of tumor necrosis factor-alpha (TNF-alpha), a product of activated macrophages, on the release of arachidonate from dispersed anterior pituitary cells. Primary cultures of anterior pituitary cells from rats were preincubated with [H-3]arachidonate to label their phospholipid-containing components. The cells were then washed and incubated with vehicle or test agents, and PRL release into the medium and [H-3]arachidonate cleaved from phospholipid were measured. TNF-alpha significantly increased the release of both PRL and [H-3] arachidonate release in a time- and dose-dependent manner. Other cytokines, such as interleukin-1-alpha, interleukin-1-beta, and gamma-interferon, had no effect on [H-3]arachidonate release. To define the role of calcium in TNF-alpha-induced arachidonate release, dispersed pituitary cells were incubated with low calcium medium, which decreased arachidonate release in response to TNF-alpha. TNF-alpha potentiated the release of [H-3]arachidonate and PRL promoted by phospholipase-A2 and melittin, and markedly shifted the dose-response curve to the left. Inhibitors of phospholipase-A2, such as p-bromophenacyl bromide and quinacrine, had no effect on TNF-alpha-induced [H-3]arachidonate and PRL release. BW755C, an inhibitor of the conversion of arachidonate to its metabolites, decreased TNF-alpha-induced PRL release, while indomethacin, a prostaglandin synthesis inhibitor, had no effect on TNF-alpha-induced PRL release. These data indicate that arachidonate metabolites may be involved in the process of TNF-alpha-induced PRL release.