The effects of insulin and beta-adrenergic stimulation on glucose transport, glut 4 and PKB activation in the myocardium of lean and obese non-insulin dependent diabetes mellitus rats

Glucose uptake, glut 4 translocation and activation of protein kinase B wer e measured in Langendorff perfused hearts from (i) Wistar control, (ii) lea n, neonatal Streptozotocin induced (Stz) and (iii) Zucker (fa/fa) obese dia betic rats of 10-12 weeks old. Hearts were subjected to stimulation with in sulin, isoproterenol (beta -adrenergic agonist) or a combination of insulin and isoproterenol, during the perfusion protocol. Basal myocardial glucose uptake was impaired in both diabetic models, but could be stimulated signi ficantly by insulin. In the Zucker rats, the time-course of insulin action was delayed. Insulin and beta -stimulation of glucose uptake were not addit ive. Evaluation of sarcolemmal membranes from these hearts showed that the affinity of glut 4 was significantly lower in the Zucker but not in the Stz hearts while a reduced affinity found with a combination of insulin and be ta -stimulation in control hearts, was absent in both diabetic models. Tota l membrane lysates were analyzed for glut 4 expression while an intracellul ar component was generated to quantify translocation on stimulation as well as activity of protein kinase B (PKB). At this age, the neonatal Streptozo tocin induced diabetic animals presented with more faulty regulation concer ning adrenergic stimulated effects on elements of this signal transduction pathway while the Zucker fa/fa animals showed larger deviations in insulin stimulated effects. The overall response of the Zucker myocardium was poore r than that of the Stz group. No significant modulation of beta -adrenergic signaling on insulin stimulated glucose uptake was found. The PI-3-kinase inhibitor wortmannin, could abolish glucose uptake as well as PKB activatio n elicited by both insulin and isoproterenol.