Relationship between autonomic cardiac activity, β-cell function, anthropometrics and metabolic indices in type II diabetics

OBJECTIVE: Recent studies have demonstrated that C-peptide exerts beneficial effects on the diabetic state, including improvements in kidney and nerve function. Thus, we investigated the effect of residual pancreatic C-peptide secretion on the cardiac autonomic nervous system in well- and poorly controlled type II diabetic patients. DESIGN: Randomised cross-sectional study. PATIENTS: Forty type II diabetic patients free from diabetic neuropathy, with similar anthropometric parameters, volunteered for our study. MEASUREMENTS: Insulin action, residual pancreatic C-peptide secretion and the cardiac autonomic nervous system were investigated by euglycaemic hyperinsuli-naemic clamp, glucagon bolus test and heart rate variability, respectively. M-values were used as an index of insulin sensitivity. High frequency (HF) and low frequency (LF) oscillations in heart rate were analysed. RESULTS: The patients were categorized into those with good (HbA_1c ≤ 7.0) and poor (HbA_1c ≥ 8.0) metabolic control. The patients with good metabolic control had fasting plasma glucose and C-peptide levels, plasma area under the curve (AUC) insulin and C-peptide levels, M-values, LF values and LF/HF ratio significantly lower than patients with poor metabolic control. In contrast, RR interval, total power and HF values had an opposite trend. Basal plasma C-peptide correlated with LF/HF in patients with good (r = -0.42; P <0.05) and poor metabolic control (r = -0.45; P <0.05). An even stronger correlation between AUC C-peptide and LF/HF in patients with good (r = -0.53, P <0.002) and poor metabolic control (r = -0.49; P <0.03), as well as in the whole group (r = -0.83; P <0.001) was found. By multiple regression analyses performed in all patients, LF/HF were independently associated with AUC C-peptide (t = -8.618; P <0.001) but not basal C-peptide levels (t = -0.137; P <0.88). CONCLUSION: Our study demonstrated that preserved C-peptide secretion is associated with a well balanced cardiac autonomic activity in type II diabetic patients.