Effects on glucose-induced insulin secretion of lipoxygenase-derived metabolites of arachidonic acid.

Our previous data suggested that lipoxygenation of endogenously released arachidonic acid (AA) is a critical step in stimulus-secretion coupling in the pancreatic beta cell. In the current study using monolayer cultures of neonatal rat islet cells, exogenous arachidonic acid (AA) (5 micrograms/ml) potently stimulated insulin release in the presence of a substimulatory glucose concentration, and potentiated release induced by glucose. Since the latter stimulatory effect of AA is prevented by inhibitors of the lipoxygenase pathway, we examined the effects of various lipoxygenase pathway products on glucose-induced insulin secretion. The mediator was not one of the stable end-products of either limb of the lipoxygenase pathway: 12- or 5-hydroxyeicosatetraenoic acid (HETE) (0.5-2000 ng/ml) did not alter insulin release, whereas 11-HETE, 15-HETE, leukotriene (LT)B4 and the delta 6 trans isomers of LTB4, LTC4 and 11-trans LTC4 all inhibited insulin release. Furthermore, diethylcarbamazine, a selective leukotriene synthesis inhibitor, did not prevent AA- or glucose-induced insulin release, arguing against a role for LTs as the mediator of AA's stimulatory effect. However, the unstable intermediate 12-hydroperoxyeicosatetraenoic acid (12-HPETE), and positional isomers of 12-HPETE, potentiated glucose-induced insulin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)