70 consecutive caucasian offsprings of type 2 diabetic subjects, admitted to our department, were screened. In all subjects, after an overnight fast, oral glucose tolerance tests (OGTTs) was performed: samples blood for glucose and plasma insulin were collected before and 2 h after a glucose load consisting of 75 g glucose anhydrate in 300 ml of water ingested over the course of 5 min. Also, fasting plasma insulin was measured to evaluate the insulin-resistance by the homeostasis model assessment-index (HOMA-I). Among them, 50 caucasian subjects (age: 47.71 ± 9.96 years, 32 men and 18 women), with normal OGTTs, were admitted in this study and were divided in two groups: offsprings with insulin resistance and offsprings without insulin resistance:
Subjects with hypertension , diabetes mellitus, impaired fasting glycemia, impaired glucose tolerance , obesity, dyslipidemia, cardiac arrhythmias, microalbuminuria and with drug treatment or diseases that could potentially disturbs carbohydrate metabolism (glucocorticoids, furosemide, beta-blockers, etc.) and cardiac autonomic activity (beta-blockers, anti-arrhythmics, ACE-inhibitors) were excluded.
The control group consisted of 25 sex and age matched healthy non insulin resistant subjects with normal OGTTs and without familiarity for type 2 diabetes mellitus.
Height, weight and body circumferences were measured on all subjects. Body mass index (BMI, kg/m2) was calculated as weight divided by height squared. Waist-to-hip ratio (WHR) was defined as waist circumference divided by hip circumference.
Informed consent was obtained from all participants; all the investigations were performed in accordance with the participants of the Declaration of Helsinki.
The insulin-resistance was evaluated by the homeostasis model assessment index (HOMA-I) [25–28]. The HOMA-I was calculated by the formula: fasting plasma glucose (mmol/L) x fasting plasma insulin (μU/ml)/ 22,5, as described by Matthews and coworkers . Insulin-resistance was defined as the third and fourth quartiles of HOMA-I.
The index subject were subdivide into two groups based on HOMA-I: 1) group of insulin-resistant offsprings (IR); 2) group of non insulin-resistant offsprings (NIR).
Autonomic nervous activity was evaluated by heart rate variability (HRV) analysis during 24-hour ECG recording. All Holter recordings were performed using a three-channel recorder. Autonomic nervous activity was analysed following the recommendations of the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology . Spectral estimates of R-R interval were obtained from stationary regions free of ectopic beats and technical artefacts. The standard deviation of normal-to-normal RR intervals (SDNN) (ms) and the square root of the mean of the sum of the squares of differences between adjacent NN intervals (RMS-SD), correlated with parasympathetic system, were calculated and were divided in two periods: night (0 am – 6 am) and day (7 am – 9 pm). Fast Fourier Transform was used to obtain power spectral estimates of HRV. Total power in the frequency range (0 – 0.40 Hz) was divided into low frequency (LF: 0.04 – 0.15 Hz, modulated by sympathetic system) and high frequency (HF: 0.15 – 0.40 Hz, modulated by parasympathetic system). The power of LF and HF components was considered in normalized units (n.u.). Subjects were analysed for 24 hours, at 10 minutes interval. Artificial data and arrhythmic were excluded. The day was divided in four periods: night (0 am – 6 am), morning (7 am – 12 am), afternoon (1 pm – 6 pm), evening (7 pm – 11 pm). Data analyses were performed with software Del Mar Avionics Accuplus 363, Irvine California, USA.
All analysis were done with SPSS 12.0 (SPSS Inc., Chicago, IL, USA) for Windows XP. Data are presented as means + SD. For data with multiple time points, variables were analysed by the general linear model ANOVA and simple regression analyses were carried out by standard techniques 95% confidence intervals (CT) were calculated for regression coefficient. Means values were considered significant at p < 0.05.