Autonomic nervous system responses to hypo- and hyperglycemia in type 2 diabetes and prediabetes.

Objective: Previous research points to a role of the brain in the regulation of glucose and pathogenesis of type 2 diabetes (T2D) via modulation of counter-regulatory hormone secretion and activity in the autonomic nervous system (ANS). The aim of this study was to investigate glucose-dependent responses of catecholamines and ANS activity in individuals with T2D, prediabetes (PD), and normoglycemia (NG).

Design: Cross-sectional.

Methods: Individuals with T2D (n = 19, 7 men, HbA1c 49 mmol/mol), PD (n = 18, 8 men), and NG (n = 17, 3 men) underwent 1 stepwise hyperinsulinemic-euglycemic-hypoglycemic and 1 hyperglycemic clamp with repeated measurements of catecholamines, symptoms, heart rate variability (HRV), and hemodynamics.

Results: The hypoglycemic response of adrenaline was augmented in T2D and PD vs NG (both P < .05), and there was a strong association with insulin resistance (P < .05 for M-value). In relation to achieved glucose levels in both clamps, noradrenaline exhibited a steeper rise during hypoglycemia in T2D vs NG and PD (both P < .05). There were trends toward more marked autonomic hypoglycemic symptoms in T2D vs PD and NG. By contrast, insulin resistance was associated with attenuated responses of heart rate and HRV indices PLF and PHF at the target glucose plateau of 2.7 mmol/L (P < .05), independent of BMI and HbA1c.

Conclusion: Alterations in glucose-dependent responses of counter-regulatory hormones and the ANS appear before, and probably contribute to, the onset of T2D. Together with other reported alterations in neuroendocrine pathways, the findings suggest that a maladaptation of the brain's responses to glucose fluctuations is important in T2D progression.