Lewis Landsberg

Fasting, Feeding and Regulation of the Sympathetic Nervous System

THE importance of catecholamines in the regulation of metabolic processes has been recognized for over 50 years. Catecholamines influence metabolism in two major ways: they increase the rate of cel...

RELATION OF OBESITY AND DIET TO SYMPATHETIC NERVOUS SYSTEM ACTIVITY

The hypothesis that dietary intake and obesity stimulate the sympathetic nervous system was investigated in a cross-sectional study of 572 men aged 43-85 years from the Normative Aging Study. Habitus was represented by body mass index, as a measure of overall adiposity, and by the ratio of abdomen-to-hip circumference (abdomen/hip ratio), as a measure of centripetal fat distribution. Sympathetic activity was assessed by measurement of 24-hour urinary norepinephrine excretion. Increased body mass index and total caloric intake were independently associated with increased 24-hour urinary norepinephrine excretion (p=0.0001 andp=0.0055, respectively). In addition, mean urinary norepinephrine excretion was higher in subjects classified as either hyperglycemic (serum fasting glucose 2:113 mg/dl) and hyperinsulinemic (serum fasting insulin >19 /tIU/ml) (p=0.0023) or in subjects classified as either hyperglycemic or hyperinsulinemic (/>=0.0063) than the mean urinary norepinephrine excretion in normal subjects. These relations were demonstrated to be independent of age, smoking status, and physical activity. Our results are consistent with the hypothesis that insulin mediates sympathetic stimulation in response to dietary intake and increases sympathetic nervous system activity in the obese.

Autonomic Regulation of Thermogenesis

Adaptive thermogenesis has been best studied in the context of temperature regulation during cold exposure. It is well established that the maintenance of constant body temperature in the face of environmental cold depends upon adaptive changes in heat production, and that the biological processes involved are under the precise control of the central nervous system. Although the somatic motor system contributes to temperature regulation, the primary importance of the autonomic nervous system in the regulation of thermogenesis is well recognized. The sympathetic nervous system, in particular, and to a lesser extent the adrenal medulla, appear to play the major role in the regulation of mammalian thermogenesis. The parasympathetic system may also participate in the regulation of thermogenic processes, but the role of this portion of the autonomic system is, at present, less clearly defined.