Thiazolidinediones improve insulin sensitivity in adipose tissue and reduce the hyperlipidaemia without affecting the hyperglycaemia in a transgenic model of type 2 diabetes

Aim/hypothesis. The aim of this study was to examine the effects of thiazolidinediones on the MKR mouse model of type 2 diabetes. Methods. Six-week-old wild-type (WT) and MKR mice were fed with or without rosiglitazone or pioglitazone for 3 weeks. Blood was collected from the tail vein for serum biochemistry analysis. Hyperinsulinaemic-euglycaemic clamp analysis was performed to study effects of thiazolidinediones on insulin sensitivity of tissues in MKR mice. Northern blot analysis was performed to measure levels of target genes of PPAR γ agonists in white adipose tissue and hepatic gluconeogenic genes. Results. Thiazolidinedione treatment of MKR mice significantly lowered serum lipid levels and increased serum adiponectin levels but did not affect levels of blood glucose and serum insulin. Hyperinsulinaemic-euglycaemic clamp showed that whole-body insulin sensitivity and glucose homeostasis failed to improve in MKR mice after rosiglitazone treatment. Insulin suppression of hepatic endogenous glucose production failed to improve in MKR mice following rosiglitazone treatment. This lack of change in hepatic insulin insensitivity was associated with no change in the ratio of HMW : total adiponectin, hepatic triglyceride content, and sustained hepatic expression of PPAR γ and stearoyl-CoA desaturase 1 mRNA. Interestingly, rosiglitazone markedly enhanced glucose uptake by white adipose tissue with a parallel increase in CD36, aP2 and GLUT4 gene expression. Conclusions/ interpretation. These data suggest that potentiation of insulin action on tissues other than adipose tissue is required to mediate the antidiabetic effects of thiazolidinediones in our MKR diabetic mice.