The present study was undertaken to assess the effects of hydroxylamine, a nitric oxide (NO) donor, on ionic and secretory events in rat pancreatic islets. Hydroxylamine provoked a concentration-dependent inhibition of the glucose-induced insulin release. This inhibitory action was counteracted by glibenclamide. Moreover, hydroxylamine increased the rate of 86Rb outflow from perifused islets. This effect persisted in the absence of external Ca2+ but was impaired by glibenclamide. Hydroxylamine decreased 45Ca outflow, [Ca2+]i and insulin output from islets exposed to 16.7 mM glucose and extracellular Ca2+. By contrast, hydroxylamine did not affect the increase in 45Ca outflow and [Ca2+]i evoked by K+ depolarization. These experimental results suggest that the negative insulinotropic action of the NO donor results, at least in part, from the activation of ATP-sensitive K+ channels leading to a decrease in Ca2+ influx and [Ca2+]i. Additional mechanisms, however, could also be involved in the NO donor modulation of the secretory process.