Based on reports that copper deficiency can result in altered arachidonic acid (AA) metabolism and the knowledge that AA can modulate insulin secretion, we investigated the interaction of copper deficiency and AA on glucosestimulated insulin secretion by using isolated islets. Lean male (Fa/Fa) Zucker rats were fed either a copper-adequate (Cont) or low-Cu (Cu Defic) diet (8.7 vs. 0.5 μg coppedg diet) for 5 weeks. Pancreatic islets were isolated and incubated in medium containing 3.3, 8.3, or 16.7 mM glucose with or without 100 μM AA. Insulin secretion was measured after either 5 (phase I) or 45 (phase 11) min of incubation. In the absence of AA, islets from Cu Defic rats secreted more insulin during phase I than those from Cont rats; phase II insulin secretion was similar between the groups. Exogenous AA treatment increased insulin secretion from islets during both phases of insulin secretion, regardless of dietary copper treatment. In the presence of AA, islets from Cu Defic rats secreted more insulin in phase I than did islets from Cont rats at the 3.3 and 8.3 mM glucose levels. Similar findings were made for phase II insulin secretion. Consistent with this, Cu Defic rats tended to have higher plasma insulin levels than Cont rats (472.6 vs. 199.6 pM). In summary, Cu deficiency increases insulin release in isolated islets; this response is particularly pronounced when AA is present in the incubation medium.