Ciglitazone reverses cAMP-induced post-insulin receptor resistance in rat adipocytes in vitro

Ciglitazone (cig), a thiazolidine-dione, lowers glucose and insulin levels in animal models of diabetes type II but not in controls. Since catecholamines given to rat adipocytes in vitro induce insulin resistance similar to that seen in type II diabetes in vivo, we measured the effect of cig on mono-A14-[125I]insulin binding and 3-O-methyl-D-glucose transport (GT) in isolated rat adipocytes treated with isoprenaline (iso, 10 microM). Cig (less than or equal to 5 microM) reversed (ED50 10 nM) the inhibitory effect of iso on insulin stimulation of GT. It had no effect on either basal or insulin stimulated GT. Furthermore, cig did not influence insulin binding either in the presence or absence of iso, which indicates that cig acts only on a post-insulin receptor level. Cig also reversed the inhibition of GT by both forskolin, a cyclase activator and RO20-1724, an imidazolidine phosphodiesterase inhibitor but not that of db-cAMP. It thus seems that cig does not act within the cAMP system but only neutralizes its inhibitory effect on the insulin stimulation of GT.