The role of arachidonic acid (AA) and its lipoxygenase metabolites in gonadotropin releasing hormone (GnRH) induced α-subunit gene expression was investigated in the transformed gonadotroph cell line αT3-1. The stable analog [d-Trp6]GnRH (GnRHa) stimulated [3H]AA release from prelabeled cells after a lag of 1–2 min. Addition of AA stimulated α-subunit mRNA levels in a dose-dependent manner, a significant effect being detected at 5 μM AA. Among various lipoxygenase metabolites of AA, only the 5-lipoxygenase products 5-hydroxyeicosatetraenoic acid (5-HETE) and leukotriene C4 (LTC4) stimulated α-subunit mRNA levels. However, while 5-HETE and LTC4 (0.1 nM each) were active already after 30 min of incubation, similar to GnRHa, AA (20 μM) stimulated α-mRNA levels after 1 h of incubation. Addition of the phospholipase A2 inhibitor 4-bromophenacyl bromide (BPB) or the selective 5-lipoxygenase inhibitor L-656,224 inhibited GnRHa elevation of α-subunit mRNA by 65%, while the cyclooxygenase inhibitor indomethacin had no effect. Addition of AA (20 μM) or LTC4 (0.1 nM) to normal cultured rat pituitary cells mimicked the rapid (30 min) stimulatory effect of GnRH (1 nM) upon α-subunit, LHβ, and FSHβ mRNA levels, while 5-HETE (0.1 nM) stimulated only FSHβ mRNA levels at this time point. Thus AA and selected 5-lipoxygenase products, in particular LTC4, participate in GnRHa-induced α-subunit mRNA elevation.
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