The altered glucose utilization in cardiocytes isolated from streptozotocin (STZ)-induced diabetic rats and its reversibility to normal following 2-week insulin treatment were studied. 3-O-Methylglucose (3-O-MG) transport in cardiocytes isolated from normal rats was stimulated to 150% (P less than 0.01) above the basal level in the presence of 80 nM insulin. The basal 3-O-MG transport in diabetic rats was decreased to 41% of that in normal rats, and further an increase in 3-O-MG transport was not observed even in the presence of 80 nM insulin. Similar significant decreases in glucose uptake in the presence of both trace (0.8 microM) and 5.5 mM glucose were also found in diabetic rats. However, in normal rats, lactate release into the media was stimulated by only 16% (P less than 0.05), and glucose oxidation was not stimulated in the presence of insulin, there being no significant difference between normal and diabetic rats. On 2-week insulin treatment of diabetic rats, both the basal 3-O-MG transport and glucose uptake in the presence of trace and 5.5 mM glucose returned to normal levels, with significant improvement of the blunted acute insulin action. In addition, both lactate release and glucose oxidation were also significantly (P less than 0.05) increased by in vivo insulin treatment. The maximum insulin-stimulated 3-O-MG transport (r = -0.79, P less than 0.01) and glucose uptake in cells in the presence of 5.5 mM glucose (r = -0.74, P less than 0.01) both showed a negative correlation with the plasma glucose concentration, but not with the plasma free fatty acid level or the plasma triglyceride level.(ABSTRACT TRUNCATED AT 250 WORDS)