Adrenocorticotropic Hormone Stimulation in Postural Orthostatic Tachycardia Syndrome (POTS)

This study is to determine different chemical levels in the blood during a low salt diet. This study will compare normal volunteers to those with Postural Tachycardia Syndrome (POTS)

Patients with postural tachycardia syndrome had a subnormal increment in aldosterone with upright posture, which might reflect a blunted adrenal response to stimulation upon assuming upright posture. In this AIM, we propose to assess the adrenal response to aldosterone stimulation with intravenous adrenocorticotropin hormone. For this protocol, subjects enrolled in the parent study will be approached about this sub-study. Subjects will be assured that they are not required to participate in this study even if they choose to participate in the parent study. There will be no randomization for this specific sub-study. The order of diets (low sodium vs. high sodium) will be performed as a part of the parent study, and not as a part of this sub-study. This sub-study will only be performed in the LOW dietary salt phase. All subjects will be previously screened and evaluated as a part of the parent study. No further screening will be performed exclusively for this study. Women of childbearing potential will have had a serum pregnancy test as a part of the parent study. Pregnant women will not be allowed to participate.

Each participant will be asked to sit in a chair for 30 minutes prior to a blood draw. Then a small dose of cosyntropin is administered intravenous. Blood samples will be drawn again at 30 minutes and 60 minutes after the drug has been given.

Each participant will be asked to sit in a chair for 30 minutes prior to a blood draw. Then a small dose of cosyntropin is administered intravenous. Blood samples will be drawn again at 30 minutes and 60 minutes after the drug has been given.

After 30 minutes of rest in the seated position, participants will be given cosyntropin intravenously. Blood samples will be taken 30 minutes pre-drug administration, 30 minutes post and 60 minutes post drug administration.

To assess the adrenal responsiveness to adrenocorticotropin hormone (ACTH), as measured by plasma aldosterone level, is contributing to the pathophysiology of Orthostatic Tachycardia.

Inclusion Criteria: Subjects will be enrolled in the parent study "Dietary Salt in Postural Tachycardia Syndrome" during the "LOW SALT" phase Postural Tachycardia Syndrome Diagnosed with postural tachycardia syndrome by the Vanderbilt Autonomic Dysfunction Center Increase in heart rate ≥30 beats/min with position change from supine to standing (10 minutes) Chronic symptoms consistent with POTS that are worse when upright and get better with recumbence Control Subjects Healthy, non-obese, non-smokers without orthostatic tachycardia Selected to match profiles of POTS patients (gender, age) Not using vasoactive medication Age between 18-50 years Male and female subjects are eligible. Able and willing to provide informed consent Exclusion Criteria: Overt cause for postural tachycardia (such as acute dehydration) Inability to give, or withdrawal of, informed consent pregnant Other factors which in the investigator's opinion would prevent the subject from completing the protocol.