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

Abstract

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. Randomised cross-sectional study. Forty type II diabetic patients free from diabetic neuropathy, with similar anthropometric parameters, volunteered for our study. Insulin action, residual pancreatic C-peptide secretion and the cardiac autonomic nervous system were investigated by euglycaemic hyperinsulinaemic 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. The patients were categorized into those with good (HbA1c < or = 7.0) and poor (HbA1c > or = 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). Our study demonstrated that preserved C-peptide secretion is associated with a well balanced cardiac autonomic activity in type II diabetic patients.