Inclusion Criteria:  Enrolled in the study "The Effect of alpha1- adrenergic receptor antagonist Therapy on Cardiac and Striatal Transporter Uptake in Pre-Motor and Symptomatic Parkinson's Disease" (STUDY #000540) Capacity to give informed consent  Exclusion Criteria:  Secondary Parkinsonism, including tardive Concurrent dementia defined by a score lower than 22 on The Montreal Cognitive Assessment (MoCA) Concurrent severe depression defined by a Beck Depression Inventory-Fast Screen (BDI fast screen) score greater than 13 Comorbidities related to sympathetic nervous system (SNS) hyperactivity Heart failure (LVEF <45%) Recent myocardial revascularization (<12 weeks) Hypertension (systolic blood pressure SBP>150mmHg (millimeters of mercury) or diastolic blood pressure DBP>100mmHg) Chronic Atrial fibrillation Concurrent Use of Beta-adrenergic antagonist Diabetes mellitus Chronic Obstructive Pulmonary Disease (COPD) Untreated Sever Sleep Apnea; Apnea-Hypopnea Index (AHI) > 30/h. Severely reduced kidney function (Glomerular Filtration Rate<30ml/min) Contraindications to the use of terazosin Recent myocardial infarction (<48 h) Ongoing angina pectoris Cardiogenic shock or prolonged hypotension Breast-feeding Current use of phosphodiesterase type 5 inhibitors: sildenafil (ViagraTM), tadalafil (CialisTM), or vardenafil (LevitraTM) History of priapism (persistent and painful erection) Neurogenic orthostatic hypotension defined as symptomatic decrease in BP > 20mmHg systolic or > 10mmHg diastolic and HR increase < 20bpm on supine to sitting or standing. Blood pressure less than 110 mm Hg systolic at screening or baseline visit Use of investigational drugs within 30 days before screening For female participant, pregnancy, or plans for child-bearing during study period Allergy/hypersensitivity to iodine or study medication