Islet phospholipase A(2) activation is potentiated in insulin resistant mice

Insulin resistance is followed by an islet adaptation resulting in a compensating increase in insulin secretion and hyperinsulinemia. The mechanism underlying this increased insulin secretion is not established. We studied whether islet phospholipase A(2) (PLA(2)) contributes by using C57BL/6J mice fed a high-fat diet, since we previously showed that the insulin responses to the two PLA(2)-activating insulin secretagogues carbachol and cholecystokinin (CCK) are enhanced in this model. CCK (100 nM) and carbachol (100 microM) stimulated [(3)H]AA efflux, reflecting PLA(2) activation, both in islets from mice after 12 weeks on high-fat diet and in controls. The efflux increase was more pronounced in islets from high-fat diet-fed mice during both CCK (by 93 +/- 46%; P = 0. 034) and carbachol (by 64 +/- 22%; P = 0.009) stimulation. Also a direct PLA(2) activation by mellitin (2 microg/ml) elicited a potentiated efflux in islets from the insulin-resistant mice (by 361 +/- 107%; P = 0.002). The results suggest that exaggerated non-glucose-induced PLA(2) activation contributes to the islet compensation in insulin resistance.