Neuroendocrine responses to hypoglycaemia decrease within the first year after diagnosis of type 1 diabetes

Abstract

Neuroendocrine responses (adrenaline, noradrenaline and pancreatic polypeptide (PP)) to hypoglycaemia are often diminished in long-term diabetic patients, but the role of autonomic nervous system changes in these reductions is not yet fully clarified. In order to establish whether such changes in neuroendocrine responses occur early in the course of diabetes, we investigated the responses to insulininduced hypoglycaemia during the first year of type 1 diabetes. Autonomic and somatic nerve function tests were performed concomitantly. Six type 1 diabetes patients were studied 3 and 12 months after diagnosis of diabetes. Hypoglycaemia was induced by i.v. insulin infusion after an overnight normalization of blood glucose. Autonomic nerve function was evaluated by cardiovascular tests, and somatic nerve function by nerve conduction velocities. A 50% reduction was found in adrenaline (p< 0.025) and noradrenaline (p< 0.05) responses to hypoglycaemia; PP, too, was significantly diminished at 12 months compared with 3 months after diagnosis of type 1 diabetes. Rate of glucose recovery did not differ at month 12 compared with month 3. Cardiovascular autonomic nerve function tests did not change and remained within the normal range throughout the study. Altered neuroendocrine responses to hypoglycaemia may occur early in the course of type 1 diabetes. These are unlikely to be due to structural changes (i.e. autonomic neuropathy), but rather to changes in central nervous system activity patterns, i.e. a higher threshold (i.e. a lower blood glucose level) for hypothalamic activation of the sympathoadrenal system.