The hypothesis that arachidonate metabolites participate in the regulation of insulin secretion by isolated pancreatic islets from the rat will be evaluated by 4 sets of experiments: I) We have demonstrated islets synthesis of some lipoxygense and cyclo-oxygenase products. The possible synthesis of additional (e.g. monoxygenase derived) metabolites will be assessed by preparation of labelled (3H,2H, and 14C) standards of the compounds of interest and comparison of these materials to islet-derived products by sequential high performance liquid chromatographic and gas chromatographic mass spectrometric (GC-MS) analyses. II) We have demonstrated that glucose stimulates islet synthesis of lipoygenase and cycloxygenase products (measured by GC-MS methods) at a concentration which maximally stimulates insulin secretion (measured by RIA). This secretagogue effect on concomitantly measured insulin secretion and arachidonate metabolite synthesis will be examined as a function of a) time after exposure to glucose and of b) glucose concentration, c) with glucose isomers and analogs and with other secretagogues, and d) for any additional arachidonate metabolites (such as monoxygenase products) identified as above. III) We have demonstrated that eicosa-(5,8,11,14)-tetrynoic acid (ETYA) (20uM) suppresses both glucose-induced insulin secretion and islet synthesis of lipoxygenase and cyclooxygenase products. This effect of inhibitors of arachidonate metabolism on insulin secretion and metabolite synthesis will be examined: a) with inhibitors of arachidonate lipoxygenases, cyclooxygenase, and monoxygenases, b) as a function of inhibitor concentration, c) as a function of time after exposure to secretagogue and of secretagogue concentration, and d) with several secretagogues. IV) The influence of exogenous standards of arachidonate metabolites on insulin secretion will be examined as a function of a) metabolite concentration, b) time after exposure to the metabolite, and c) concentration of glucose. These studies may broaden understanding of biochemical events regulating insulin secretion and suggest pharmacologic means for manipulation of these processes in diabetes mellitus.
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