OVERFEEDING, AUTONOMIC REGULATION AND METABOLIC CONSEQUENCES

The autonomic nervous system plays an important role in the regulation of body processes in health and disease. Overfeeding and obesity (a d isproportional increase of the fat mass of the body) are often accompa nied by alterations in both sympathetic and parasympathetic autonomic functions. The overfeeding-induced changes in autonomic outflow occur with typical symptoms such as adiposity and hyperinsulinemia. There mi ght be a causal relationship between autonomic disturbances and the co nsequences of overfeeding and obesity. Therefore studies were designed to investigate autonomic functioning in experimentally and geneticall y hyperphagic rats. Special emphasis was given to the processes that a re involved in the regulation of peripheral energy substrate homeostas is. The data revealed that overfeeding is accompanied by increased par asympathetic outflow. Typical indices of vagal activity (such as the c ephalic insulin release during food ingestion) were increased in all o ur rat models for hyperphagia. Overfeeding was also accompanied by inc reased sympathetic tone, reflected by enhanced baseline plasma norepin ephrine (NE) levels in both VMH-lesioned animals and rats rendered obe se by hyperalimentation. Plasma levels of NE during exercise were, how ever, reduced in these two groups of animals. This diminished increase in the exercise-induced NE outflow could be normalized by prior food deprivation. It was concluded from these experiments that overfeeding is associated with increased parasympathetic and sympathetic tone. In models for hyperphagia that display a continuously elevated nutrient i ntake such as the VMH-lesioned and the overfed rat, this increased sym pathetic tone was accompanied by a diminished NE response to exercise. This attenuated outflow of NE was directly related to the size of the fat reserves, indicating that the feedback mechanism from the periphe ry to the central nervous system is altered in the overfed state.