A Possible Role for Lipoxygenase and Epoxygenase Arachidonate Metabolites in Prolactin Release from Pituitary Cells

Abstract

We studied the effects of selected leukotrienes and hydroxyeicosatetraenoic acids (HETEs) on prolactin release from primary cultures of female rat anterior pituitary cells. Leukotrienes B4, C4, and D4 had no effect on basal prolactin release; however, they did enhance prolactin release that was stimulated by 1 or 5 nM thyrotropin-releasing hormone (TRH). Leukotriene C4 also enhanced prolactin release that was induced by phorbol myristate acetate (a protein kinase C activator) by maitotoxin (a calcium uptake stimulator), and by angiotensin II. 5-HETE, 12-HETE, and 15-HETE stimulated basal prolactin release at high concentrations (1 µM and greater), and 5-HETE and 12-HETE enhanced TRH-and angiotensin II-induced prolactin release at lower (nanomolar) concentrations as well. In order to determine the role of endogenous arachidonate metabolites in prolactin release, pituitary cell cultures were exposed to selected inhibitors of the 5-lipoxygenase enzyme, which metabolizes arachidonate to leukotrienes and 5-HETE, and to those of the epoxygenase enzyme, which metabolizes arachidonate to epoxyeicosatrienoic acids. These inhibitors decreased basal and secretagogue-induced prolactin release. In additional experiments, it was determined that TRH enhances the liberation from pituitary cells of arachidonate metabolites with high-performance liquid chromatography elution profiles similar to those of leukotriene C₄ and ω-OH-leukotriene B4 (a metabolite of leukotriene B4) and the HETEs. Therefore, the production of leukotrienes, HETEs, and epoxyeicosatrienoic acids may be necessary for the normal release of prolactin.