Insulin receptor autophosphorylation and kinase activity in streptozotocin diabetic rats. Effect of a short fast.

Insulin receptor associated kinase activity and its relationships with the insulin resistance of streptozotocin-induced diabetes were investigated in rats, using solubilized, partially purified insulin receptors from liver membranes. Insulin receptor kinase activity was measured by means of both autophosphorylation and phosphorylation of the exogenous substrate Glu4:Tyr1. Diabetes was associated with a 45% reduction in kinase activity, in the same number of insulin receptors, with no change in insulin binding affinity. To investigate the independent roles of hyperglycemia and hypoinsulinemia on the observed impairment of receptor kinase activity, diabetic rats were fasted for 24 h in order to normalize blood glucose levels only. After this short fast, no change in kinase activity, from the values measured in fed diabetic animals, was observed. Our findings suggest that streptozotocin diabetes is associated with a reduction of insulin receptor kinase activity, which a short fast is not able to reverse.