Regulation of uncoupling protein-2 (UCP-2) in beta-cells is presently unclear but may involve oxidative stress. We tested for regulation by beta-cell toxic cytokines. Exposure to interleukin-1beta (IL-1beta, 10 ng/ml) for 6 h down-regulated UCP-2 mRNA in clonal INS-1 cells, by 37 +/- 7%, and in rat pancreatic islets, by 55 +/- 8%. In contrast, a 6 h exposure to IL-1beta did not affect viability as assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, or mitochondrial membrane potential, or ATP cellular contents. Continued exposure to IL-1beta was accompanied by decreased viability and persisting down-regulation of UCP-2 mRNA. Exposure to a combination of IL-1beta and tumor necrosis factor (TNF)-alpha for 48 h additively decreased cell viability and UCP-2 mRNA. The constitutive nitric oxide (NO) synthase inhibitor N-omega-nitro-L-arginine methyl ester (L-NAME, 1 mM) partially protected against toxicity but failed to significantly affect UCP-2 mRNA expression. The inducible NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 1 mM) protected completely against cytokine-induced toxicity. L-NMMA per se down-regulated UCP-2 mRNA (by 64 +/- 7%). Transfection with a UCP-2-antisense nucleotide failed to affect IL-1beta induced toxicity. In conclusion, down-regulation of UCP-2 mRNA by IL-1beta is an early event of cytokine interaction with beta-cells which is not directly coupled to toxicity.