AUTONOMIC NERVOUS-SYSTEM IN EARLY INSULIN-RESISTANCE SYNDROME

Changes in the activity of the sympathetic activity are often involved in the development of human insulin-resistance syndrom. However, the nature of changes in both the parasympathetic End orthosympathetic com ponents are still controversial. We have recently developped an experi mental model reproducing in dog this morbid triptyque !obesity, hypert ension and hyperinsulinism), obtained by hypercaloric hyperlipidic die t. The aim of the present study was to characterize the changes in aut onomic nervous system and spontaneous baroreflexe in the initial perio d of obesity-hypertension syndrom. Ten male Beagle-Harrier dogs were u sed in this study. We investigated before and during 20 weeks after th e beginning of the hypercaloric diet, plasma insulin, noradrenaline le vels, spontaneous baroreflex efficiency (using the sequence method), a rterial blood pressure, heart rate and their spectral analysis (fast F ourier Transformation) in both low (LF : 50-150 mHz, reflecting sympat hetic activity) and high (HF: respiratory rate +/- SO mHz, reflecting parasympathetic activity) frequency bands. Body weight (+ 20 %), systo lic (SBP : + 23 %) and diastolic (+ 16 %) blood pressure and heart rat e (+ 19 %) increased during 6 weeks and then remained stable. Concomit antly, 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 to ne and a early increase in sympathetic activity. Nevertheless, in stea dy state of this syndrom, parasympathetic tone returned to initial val ues (18.43 +/- 3.25 % at 20th week). Insulinemia significantly increas ed from the 4th week (14.2 +/- 0.9 vs 25.3 +/- 2.2 mu Ul/mL at 20th we ek), but noradrenaline remained not modify (400 +/- 85 vs 312 +/- 45 p g/mL at 20th week). Spontaneous baroreflex efficiency also decreased f rom 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 decr ease in both parasympathetic tone and spontaneous baroreflex efficienc y, which could be the physiopathological link between obesity, hyperte nsion and hyperinsulinism.