Fatty acids and cyclooxygenase and lipoxygenase pathway inhibitors modulate inositol phosphate formation in pancreatic islets

Isolated rat pancreatic islets prelabeled with myo-[³H]inositol respond to glucose and carbamylcholine with increased [³H] inositol phosphate (InsP) production. Prostaglandin E₂ (PGE₂) inhibits the effects of glucose and carbamylcholine on [³H]InsP production, Ionomycin reversed the effect of PGE₂ on glucose-stimulated [³H]InsP production. The cyclooxygenase inhibitors indomethacin, ibuprofen, and eicosatetraynoic acid potentiated [³H]InSP production in response to 5 and 10 mM glucose but not to 17 mw glucose. Indomethacin did not affect the carbamylcholine response. Unsaturated fatty acids, including arachidonic acid, linolenic acid, eicosapentaenoic acid, oleic acid, and eicosatetraynoic acid, increased [³H]InsP production. Arachidonic acid potentiated [³H]InsP accumulation in response to low concentrations of glucose, Indomethacin potentiated the response to arachidonic acid. Δ⁹-Tetrahydrocannabinol, which mobilizes endogenous fatty acids, also potentiated glucose-stimulated [³H]InsP production. The lipoxygenase inhibitors BW755C and nordihydroguaiaretic acid inhibited [³H]InsP production in response to glucose, carbamylcholine, and fatty acids. Thus, PGE₂ and endogenous cyclooxygenase products antagonize InsP production in islets, whereas fatty acids promote InsP accumulation.