ARACHIDONATE 12-LIPOXYGENASE IN PORCINE ANTERIOR-PITUITARY-CELLS - ITS LOCALIZATION AND POSSIBLE FUNCTION IN GONADOTROPHS

Arachidonate 12-lipoxygenase, which oxygenates positions 12 and 13 of arachidonic and linoleic acids, is present in porcine anterior pituita ry cells. Colocalization of the 12-lipoxygenase with various pituitary hormones was examined by immunohistochemical double-staining using an tibodies against 12-lipoxygenase and various anterior pituitary hormon es. Under light microscopy, approximately 7% of the cells producing lu teinizing hormone (LH) and follicle-stimulating hormone (FSH) were pos itive for 12-lipoxygenase, whereas the enzyme was detected in less tha n 2% ofthe cells producing thyrotrophin, prolactin, growth hormone (GH ), and adrenocoaicotrophin. In an attempt to examine the participation of 12-lipoxygenase metabolites in pituitary hormone release, we incub ated the primary culture of porcine anterior pituitary cells with 12-h ydroperoxy-arachidonic acid or 13-hydroperoxy-linoleic acid. Significa nt stimulation of LH and FSH release by these hydroperoxides was obser ved at 10 mu M in a time-dependent manner. At doses around 10 mu M the se compounds produced responses of similar magnitude to 1 nM gonadotro phin-releasing hormone (GnRH), but higher concentrations (30 mu M) of the compounds were required for GH release. In contrast, 12-hydroxy-ar achidonic and 13-hydroxy-linoleic acids were almost ineffective. Furth ermore, the gonadotrophin release by 1 nM GnRH was inhibited by nordih ydroguaiaretic acid (a lipoxygenase inhibitor) with an IC50 of about 5 mu M. Thus, the hydroperoxy (but not hydroxy) products of 12-lipoxyge nase may be involved in the release of pituitary hormones especially L H and FSH.