Starvation decreases insulin secretion, prostaglandin E2 production and phospholipase A2 activity in rat pancreatic islets.
Pancreatic islets, isolated from rats starved for 48 h, secreted significantly less insulin in the presence of 2 mmol glucose/l than islets of fed controls. In contrast, the insulin secretory response of islets from fed and starved rats to a challenge of 20 mmol glucose/l was similar. Concentrations of prostaglandin E2 (PGE2) in islets from starved rats incubated with 2 mmol glucose/l were significantly lower compared with those in control islets obtained from fed animals. Although glucose (20 mmol/l) stimulated PGE2 production in islets from starved and fed rats by 2.7- and 1.6-fold respectively, the concentrations achieved were the same as a consequence of the different prestimulated concentrations. Incubation with [14C]arachidonic acid of sonicated islet preparations from fed rats and separation of metabolites generated by high-pressure liquid chromatography, indicated the biosynthesis of a number of cyclo-oxygenase- and lipoxygenase-derived compounds, including 6-keto-PGF1 alpha, PGF2 alpha, PGE2 and 12-hydroxyeicosatetraenoic acid. Metabolism of arachidonic acid to cyclo-oxygenase-derived compounds occurred with the same efficiency, but production of lipoxygenase-derived compounds was reduced by 50% in sonicated islets from starved compared with fed rats. Activity of phospholipase A2 of islets from starved rats was significantly less than that measured in islets from fed rats, although the degree of stimulation by 20 mmol glucose/l was the same in both types of islet. These alterations in the phospholipase A2/arachidonic acid cascade may contribute to the diminished insulin secretory response of islets from starved rats to relatively low concentrations of glucose.