The Role of Endothelin in the Supine Hypertension of Autonomic Failure

Inclusion Criteria: * Patients with autonomic failure and supine hypertension from all races, who are in the hospital participating in the study "The Evaluation and Treatment of Autonomic Failure" (IRB# 000814). * Supine hypertension, defined as a systolic blood pressure \>150 mm Hg or diastolic blood pressure \> 90 mm Hg. * Males and females, between 18-85yr. * Provide written informed consent to participate in the study and understand that they may withdraw their consent at any time without prejudice to their future medical care. Exclusion Criteria: * Pregnant women. * High-risk patients (e.g. heart failure, symptomatic coronary artery disease, liver impairment, history of stroke or myocardial infarction). * History of serious allergies or asthma. * In the investigator's opinion, have clinically significant abnormalities on clinical, mental examination or laboratory testing. * All medical students.