Oxidative stress, followed by the apoptotic death of pancreatic beta cells, is considered to be one of causative agents in the evolution of the type 2 diabetic state; therefore, the protection of beta cells can comprise an efficacious strategy for preventing type 2 diabetes. In the present study, RIN-m5F cells (i.e. the rat insulinoma beta cell line) were stimulated with streptozotocin, resulting in a time- and concentration-dependent release of lactate dehydrogenase. There appeared to be significant apoptotic cell death after 2 h of treatment with streptozotocin at 10 mM, as demonstrated by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining and 2.6-fold activation of cellular caspase-3, an apoptotic enzyme. By contrast, some neuropeptides of the glucagon-secretin family and coenzyme Q(10), an endogenous mitochondrial antioxidant, could attenuate streptozotocin cytotoxicity, and especially pituitary adenylate cyclase-activating polypeptide (PACAP), at a concentration of 10(-7) M, exhibited 34% attenuation of lactate dehydrogenase release from streptozotocin-treated RIN-m5F cells. Quantitative RT-PCR experiments indicated the inhibitory effect of PACAP on streptozotocin-evoked up-regulation of pro-apoptotic factor (Noxa and Bax) and a 2.3-fold enhancement of Bcl-2 mRNA expression, a pro-survival protein, was also observed after addition of PACAP. The data obtained suggest the anti-apoptotic role of PACAP in streptozotocin-treated RIN-m5F cells through the regulation of pro-apoptotic and pro-survival factors.