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.
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.
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.
L-tyrosine at a dosage of 1000 mg daily (500 mg 2x daily) is safe and well tolerated in subjects receiving dopamine therapy and other anti-Parkinson’s medication. L-tyrosine at 1000 mg was enough to increase plasma tyrosine in Parkinson’s disease (PD) within a normal healthy reference range. Supplementing 1000 mg of L-tyrosine did not show any improvement in blood pressure in people with PD that suffer from orthostatic hypotension.
Presentations & Publications
This project was submitted as an abstract to the International Parkinson and Movement Disorder Society in Stockholm, Sweden in June 2014.