Objective: To investigate the nature and time course of autonomic nervous system changes elicited by a 21-week ad libitum high-fat diet (HFD) in dogs.
Results: The HFD increased body weight (+22.0+/-2.8% at week 21) with an abdominal circumference gain significantly more elevated than the thoracic one. The increases in insulin and free fatty acid plasma levels were correlated with body weight changes. Systolic and diastolic blood pressures and heart rate significantly increased (+23+/-6, +28+/-5 and 19+/-9% respectively). Arterial hypertension was characterized by an increase in cardiac output (+22.3+/-7.7%), in left ventricular mass (+18.1+/-5.0% at week 21) and a decrease in spontaneous baroreflex efficiency (-55+/-6%). The time course of autonomic changes (using spectral analysis of systolic blood pressure and heart rate) showed the existence of time-dependent modifications, which were linked with food intake. The initial rise in arterial blood pressure during body weight increment (observed between the 1st and 8th week of HFD) was associated with a transient increase in the low frequency band of systolic blood pressure variability and noradrenaline plasma levels associated with a long-lasting decrease in the high frequency band of heart rate variability. Early changes in short-term variability were significantly correlated with free fatty acid plasma levels. In contrast, the steady-state of obesity-related hypertension was associated with a decreased high frequency band of heart rate variability, without significant changes in noradrenaline plasma levels.
Conclusions: This study shows that the HFD induces abdominal obesity, hyperinsulinaemia and arterial hypertension, with a left ventricular hypertrophy associated with a biphasic changes in autonomic activity: an early and long-lasting decrease in parasympathetic nervous system activity and an early but transient increase in sympathetic activity. The present data suggest that autonomic nervous system changes are dependent on the time course of obesity development.