The Autonomic Nervous System and Obesity

The rationale for this study is that even small alterations to energy metabolism can significantly change energy balance and body weight in the long term. We will test the hypothesis that the sympathetic nervous system (SNS) activity contributes to resting and thermogenic components of energy expenditure (EE). This study is divided in four different parts: (1), (2), (3), (4). Part (1): we will gauge the contribution of the sympathetic nervous system to resting energy expenditure, blood pressure, and determine differences between lean, obese, and patients with primary autonomic failure . Part (2): we will determine the degree of sympathetic blockade by a gradual infusion of the ganglionic blocker trimethaphan.\[Part 2 has been closed\] Part (3): we will determine the energy balance in patients with primary autonomic failure. Part (4): we will determine the contribution of the sympathetic nervous system to lipolysis.\[Part 4 has been closed\] Subjects selections\*: For part (1) and (2) we will study six groups of subjects (n = 40 for each group): patients with pure autonomic failure, patients with multiple system atrophy, healthy normal controls (BMI \<= 25), obese controls (BMI 30-40) and obese hypertensive (BMI 30-40) and lean hypertensive (BMI 20-28). A time interval of at least 1 week is required for those subjects who wish to participate in part (1) and part (2). For part (3) we will study two groups of subjects (n=12 for each group): patients with autonomic failure, and their age sex-matched sedentary, healthy controls. For part (4) we will study two groups of subjects (n=12 for each group): healthy normal controls (BMI 20-25), obese controls (BMI 30-40). \*Part 2 and 4 have been closed.