Effect of Tyrosine on Orthostatic Hypotension in Parkinson’s Disease

Objective/Rationale: 
Orthostatic hypotension is a sudden drop in blood pressure (BP) when an individual changes position. Individuals with Parkinson’s disease (PD) commonly suffer from orthostatic hypotension and low BP due to reduced levels of the neurotransmitter norepinephrine. Medications used to treat PD (such as levodopa) reduce norepinephrine levels, thus further reducing BP. Tyrosine is a non-essential amino acid (a vitamin supplement) that is the building block for norepinephrine. Supplementing tyrosine may help to increase BP in individuals with PD.

Project Description: 
Forty subjects with PD, orthostatic hypotension and low blood pressure will keep a food diary detailing fluid and salt intake for seven days before testing. Subjects will be randomly assigned to a tyrosine supplementation group or to a placebo group. Both researchers and subjects will be blind to the treatment assignment. After an overnight fast, subjects will undergo an orthostatic hypotension test and an exercise test to induce stress at peak medication. Blood will be drawn before exercise testing and immediately post test. Heart rate and BP will be monitored every two minutes for the duration of the test. Subjects will then take seven days of tyrosine supplementation or placebo, and continue with the food diary. The same tests will be administered after seven days of tyrosine supplementation or placebo.

Relevance to Diagnosis/Treatment of Parkinson’s Disease:                     
Orthostatic hypotension and low BP are common in individuals with PD, who may experience lightheadedness, falls and reduced quality of life. Current medications used to increase BP have varied side effects and are often not tolerated well by patients. Positive findings, that supplemental tyrosine increases BP and heart rate response in people with PD during daily activities, can lead to new therapies to improve parkinsonian orthostatic hypotension.

Anticipated Outcome:          
Researchers anticipate that tyrosine can improve BP and heart rate response in individuals with PD. This could lead to an alternative approach to medication, potentially decreasing medication side effects and improving quality of life in individuals with PD.