title: Arachidonate metabolism in the mouse thyroid implication of the lipoxygenase pathway in thyrotropin action.
abstract: The present study of compares the effects of various inhibitors of arachidonate metabolism on mouse thyroid cyclo-oxygenase and lipoxygenase activities and thyrotropin-augmented cyclic-AMP accumulation. Mouse thyroid homogenate converts [1-14C]- arachidonate to several products of the cyclo-oxygenase pathway as well as one major product of the lipoxygenase pathway, 12-L-hydroxyeicosatetraenoic acid (12-Hete). Prostaglandin (PG) formation in thyroid homogenates is inhibited by 1-10 microM indomethacin and etya. 12-HETE accumulation is reduced by 91%, 83% and 20% by 5 microM ETYA, 15-HETE, and indomethacin, respectively. Thyrotropin-stimulated cyclic-AMP accumulation, measured in whole thyroid lobes by radioimmunoassay, is reduced by 45% and 73% by 50 microM and 100 microM ETYA, respectively; indomethacin is without effect at these concentrations. 15-HETE reduces thyrotropin-augmented cyclic-AMP accumulation by 57% and 100 microM. In product inhibition studies, 10 microM 12-HETE reduced the formation of radiolabeled 12-HETE by 20%. 10 microM PGE2, PGF2 alpha or PGD2 had no effect on [1-14C]-PG formation. 12-HETE, however, reduced PG synthesis by 76% at 10 microM. This is the first report implicating the arachidonate lipoxygenase pathway in thyrotropin action at the level of cyclic-AMP regulation. Additionally, our finding that 12-HETE inhibits prostaglandin synthesis suggests that the cyclo-oxygenase and lipoxygenase pathways in the mouse thyroid may be highly integrated.
mesh_terms: D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000096:biosynthesis / Q000378:metabolism* / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D006893:Hydroxyeicosatetraenoic Acids; D007213:Indomethacin / Q000494:pharmacology; D008084:Lipoxygenase / Q000378:metabolism*; D051379:Mice; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000378:metabolism*
chemical_list: D001095:Arachidonic Acids; D006893:Hydroxyeicosatetraenoic Acids; D016718:Arachidonic Acid; D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; C025984:15-hydroxy-5,8,11,13-eicosatetraenoic acid; D013972:Thyrotropin; D000242:Cyclic AMP; D008084:Lipoxygenase; D011451:Prostaglandin-Endoperoxide Synthases; D007213:Indomethacin