[Autonomic nervous system abnormalities in the initial phase of insulin resistance syndrome. Value of the study of variability of cardiac rate and blood pressure on a model of nutritional obesity].

Changes in the activity of the sympathetic activity are often involved in the development of human insulin-resistance syndrome. However, the nature of changes in both the parasympathetic and orthosympathetic components are still controversial. We have recently developed an experimental model reproducing in dog this morbid triptyque (obesity, hypertension and hyperinsulinism), obtained by hypercaloric hyperlipidic diet. The aim of the present study was to characterize the changes in autonomic nervous system and spontaneous baroreflex in the initial period of obesity-hypertension syndrome. Ten male Beagle-Harrier dogs were used in this study. We investigated before and during 20 weeks after the beginning of the hypercaloric diet, plasma insulin, noradrenaline levels, spontaneous baroreflex efficiency (using the sequence method), arterial blood pressure, heart rate and their spectral analysis (fast Fourier Transformation) in both low (LF: 50-150 mHz, reflecting sympathetic activity) and high (HF: respiratory rate +/- 50 mHz, reflecting parasympathetic activity) frequency bands. Body weight (+20%), systolic (SBP: +23%) and diastolic (+16%) blood pressure and heart rate (+19%) increased during 6 weeks and then remained stable. Concomitantly, high frequency of HR (22.01 +/- 1.9 vs 14.15 +/- 1.04% at 7th week) and BF of systolic blood pressure (15.6 +/- 1.1 vs 19.2 +/- 1.2% at 4th week); p < 0.07, showed a rapid decrease in parasympathetic tone and a early increase in sympathetic activity. Nevertheless, in steady state of this syndrome, parasympathetic tone returned to initial values (18.43 +/- 3.25% at 20th week). Insulinemia significantly increased from the 4th week (14.2 +/- 0.9 vs 25.3 +/- 2.2 microUI/mL at 20th week), but noradrenaline remained not modify (400 +/- 85 vs 312 +/- 45 pg/mL at 20th week). Spontaneous baroreflex efficiency also decreased from the 2nd week (35.5 +/- 5.5 vs 16.7 +/- 4.9 mmHg/ms at 20th week). This study shows that an hyperlipidic hypercaloric diet induces a decrease in both parasympathetic tone and spontaneous baroreflex efficiency, which could be the physiopathological link between obesity, hypertension and hyperinsulinism.