Plasma glucose concentrations were measured in: 1) conscious and anesthetized rats during an iv glucose tolerance test (IVGTT) and 2) conscious and anaesthetized phentolamine/propranolol blocked rats during an IVGTT. Anesthesia was induced with ketamine (120 mg.kg-1) or pentobarbitone (60 mg.kg-1) ip at -30 min of the beginning of the IVGTT, which was followed by 2 injections of the anesthetic agents at intervals of 30 min. Propranolol (2 mg.kg-1) was given ip at -25 and -5 min. An iv infusion of phentolamine (0.015 mg.min-1) was started at -20 min and continued up to the end of the experiment. During the IVGTT, the anesthetized rats showed a moderate hyperglycemic response to glucose load compared to conscious animals (ketamine: p < 0.01 at 5 min; and p < 0.05 at 10-20 min; pentobarbitone: p < 0.05 at 5-20 min). The hyperglycemic response to glucose administration in the conscious rats was not affected by adrenergic blockade (p > 0.05). While in ketamine anesthetized rats the increased glucose response was abolished by adrenergic blockade (p < 0.05 at 5-10 min), this effect was not seen in pentobarbitone anesthetized animals. These results suggest the existence of an inhibitory tone on insulin secretion and a glycogenolytic response in ketamine anesthetized rats, probably mediated by adrenergic inervation of the pancreas and liver and by circulating catecholamines secreted from the adrenal medulla.