ObjectiveTo study the protective effect of two thiazolidinediones (TZDs), rosiglitazone and pioglitazoneon, on the apoptosis of pancreatic islet beta-cells. MethodsMale Goto-Kakizaki (GK) rats (a spontaneously diabetic animal model of type 2 diabetes mellitus) and non-diabetic Wistar rats were randomly divided into four groups: Wistar group (W group, n=13),GK rats fed with rosiglitazone (R group, n=10), GK rats fed with pioglitazone (P group, n=10) and GK non-treated rats(G group, n=10). Rats in R group were given rosiglitazone (2 mg·kg-1·d-1) by gavage for 6 weeks; those in A group were given pioglitazone (3 mg·kg-1·d-1) by gavage for 6 weeks. The pancreatic specimens were obtained and treated for light microscope and transmission electron microscope. Bcl-2, Bax protein expression was examined by immunohistochemistry. The apoptosis of pancreatic islet beta-cell was examined by TUNEL. ResultsThe β-cells in G group showed signs of early apoptosis: nuclei shrinkage, disappearing nucleoli, and chromatin aggregation to nuclear membrane, and the changes were not observed in the other three groups. Bcl-2 expression was significantly higher in R group and P group than in G group (P<0.01), and there was no significant difference between the W group and G group. Bax expression was significantly lower in R group, P group, and W group than in G group (P<0.05), and there was no difference between the R group and P group. ConclusionIncreased β-cells apoptosis does exist in GK rat pancreatic islets, which may contribute to the development of diabetes. Rosiglitazone and pioglitazone can prevent β-cell from apoptosis, which might be related to the changes of Bcl-2 and Bax expression.