Renal Salt Handling in Postural Tachycardia Syndrome Following Dietary Dopa Administration

• Plasma dopa, urinary dopamine, urinary sodium [ Time Frame: Plasma samples collected before breakfast and 1, 2, 4 and 6 hours after breakfast on both study days. Urine collected 0-4, 4-8, and 8-12 hours after breakfast on both study days.f inpatient study days ] [ Designated as safety issue: No ]
  Subjects consumed the standard fixed sodium diet for at least two days prior to study and on study day one during an inpatient stay in the Vanderbilt Clinical Research Center. On study day two, participants ate 100 g of puréed fava beans and pods with study diet at breakfast (0800hr) and lunch (1200hr). Blood was sampled for catechol assays before and at 1, 2, 4 and 6 hours after breakfast. Three consecutive 4- hr urine samples were collected for electrolyte and catechol content.
  
  

• Other plasma catechols (norepinephrine, dopamine) [ Time Frame: Before and 1, 2, 4 and 6 hours after breakfast on both study days. ] [ Designated as safety issue: No ]
  Subjects consumed the standard fixed sodium diet for at least two days prior to study and on study day one during an inpatient stay in the Vanderbilt Clinical Research Center. On study day two, participants ate 100 g of puréed fava beans and pods with study diet at breakfast (0800hr) and lunch (1200hr). Blood was sampled for catechol assays before and at 1, 2, 4 and 6 hours after breakfast.
  
  
• Other urinary catechols (dopa, norepinephrine) [ Time Frame: 0-4, 4-8, and 8-12 hours after breakfast on both study days. ] [ Designated as safety issue: No ]
  Subjects consumed the standard fixed sodium diet for at least two days prior to study and on study day one during an inpatient stay in the Vanderbilt Clinical Research Center. On study day two, participants ate 100 g of puréed fava beans and pods with study diet at breakfast (0800hr) and lunch (1200hr). Three consecutive 4- hr urine samples were collected for electrolyte and catechol content.
  
  
• Blood pressure and heart rate [ Time Frame: Supine-before breakfast and 1, 2, 4 and 6 hours after breakfast on both study days. Upright-2 and 6 hours after breakfast on both study days. ] [ Designated as safety issue: No ]

  In the morning (0700h), while still supine after the overnight sleep, HR and BP will be recorded. Supine HR and BP will be measured by Dinamap at 0900, 1000, 1200 (before the meal), and 1400hr.

  In addition, at 1000 and 1400hr, subjects will stand for 30 minutes for upright BP and HR measurements

  
  

Fava beans are a broad bean, with potential clinical relevance in Parkinson's patients since they contain high levels of the dopamine precursor, dihydroxyphenylalanine (dopa).In addition to the central nervous system functions of dopamine that are compromised in Parkinson's disease, renal dopamine has vasodilatory and natriuretic activity. Elevated urinary dopamine, however, does not consistently correlate with increased urinary sodium excretion, and there are conflicting opinions over the conditions under which renal dopamine might regulate sodium balance.The goal of our study was to clarify the natriuretic effect of fava beans, obtained from a source that serves patients with Parkinson's disease. Catechol and sodium data were compared in healthy volunteers using a longitudinal design in which all participants consumed a fixed sodium study diet on day 1 and the fixed sodium diet plus fava beans on day 2. Blood was sampled at 1, 2, 4 and 6 hours after breakfast, and three consecutive 4-hr urine samples were collected.

Postural tachycardia syndrome (POTS) is the most common form of orthostatic intolerance, affecting an estimated 500,000 Americans, principally young women. POTS refers to an excessive increase in heart rate (>30 beats per minute) on standing in the absence of orthostatic hypotension. Previous findings by the Robertson/Garland research group suggest that mechanisms involved in orthostatic and absolute volume regulation contribute to POTS pathophysiology. A follow-up study might compare the influences of diet in patients with POTS and healthy volunteers.