Cyclic AMP, cyclic GMP and glucose utilization by diabetic rat fat cells

Fat cells from epididymal adipose tissue from normal and streptozotocin-diabetic rats were studied to determine glucose utilization and cyclic nucleotide levels. Diabetic rat fat cells present a higher cAMP content (P less than 0.05) compared with controls. Addition of insulin decreases within 10-min incubation the cAMP content in both normal and diabetic cells (P less than 0.05). However, the value obtained in the latter remains by 25% higher than that of normal cells not exposed to insulin. No changes in cGMP were detected. Pretreatment of the diabetic animals during two days with propranolol (1 mg kg body wt-1 day-1) induces the decrease to normal levels of the fat cell cAMP content. However, it persists the impairment on glucose utilization observed in fat cells from diabetic animals. It seems that the increase in the intracellular amount of cAMP found in fat cells from diabetic rats is not involved, at least directly, to the impaired glucose utilization found in the diabetic state. Furthermore, through an unknown mechanism, pretreatment with propranolol can induce a drop in fat tissue cAMP toward normal values without normalizing glucose utilization.