Arachidonic acid metabolism in isolated pancreatic islets. I. Identification and quantitation of lipoxygenase and cyclooxygenase products

The metabolism of arachidonic acid by pancreatic islets has been studied with purified populations of large numbers of islets isolated from the rat. Sequential high-performance liquid chromatographic analyses of islet-derived metabolites of ³H-labeled arachidonate in both reversed and normal phases with ¹⁴C-labeled internal standards have demonstrated synthesis by the islets of the cyclooxygenase products prostaglandin E₂, prostaglandin F_2α, thromboxane B₂ and 12-hydroxyheptadecatrienoic acid as well as the lipoxygenase product 12-hydroxyeicosatetraenoic acid (12-HETE). Islet synthesis of these compounds was suppressed with appropriate inhibitors of arachidonate metabolism. Synthesis of the identified metabolites from endogenous arachidonate has also been quantitated with the use of deuterated internal standards, capillary column gas chromatographic analyses, and negative ion-chemical ionization mass spectrometric measurements. The relative abundances of metabolites derived from exogenous, radiolabeled arachidonate versus endogenous precursor differed considerably, and 12-HETE was by far the most abundant of these metabolites synthesized from endogenous arachidonate. Platelets contaminating the isolated islet preparations have been excluded as the source of the identified arachidonate metabolites. These studies establish that cells intrinsic to pancreatic islets synthesize a clearly characterized profile of arachidonate lipoxygenase and cyclooxygenase products. The sensitive and specific mass spectrometric methods for quantitation of these compounds permit detailed evaluation of their possible participation in insulin secretion from isolated islets.