Terazosin and Parkinson's Disease Extension Study

123I-MIBG early reuptake will be measured by Heart to Mediastinal ratio (H/M) which will be calculated from the early images after drawing regions of interest (7×7 pixels) over the upper mediastinum and circular ROI around the entire heart. MIBG abnormality cutoff will be set for values of late H/M <2.2.

123I-MIBG late reuptake will be measured by Heart to Mediastinal ratio (H/M) which will be calculated from the late images after drawing regions of interest (7×7 pixels) over the upper mediastinum and circular ROI around the entire heart. MIBG abnormality cutoff will be set for values of late H/M <2.2.

123I-MIBG Washout ratio (WR) will be calculated using the following formula: [(early heart counts/pixel - early mediastinum counts/pixel) - (late heart counts/pixel decay-corrected - late mediastinum counts/pixel decay-corrected)]/(early heart counts/pixel - early mediastinum counts/pixel). Care will be taken to exclude lung or liver from the myocardial and large vessels and lung from the mediastinum region of interest. MIBG abnormality cutoff will be set for values of WR >30%.

Diagnosis of PD will be defined or ruled out according to the United Kingdom Parkinson's Disease Society Brain Bank (UKPDSBB) criteria

Measured by 123I-Ioflupane uptake, between baseline, year one, year two and year three.

Integrity of pigmented neurons of substantia nigra.

Beat-to-beat intervals will be registered to assess sympatho-vagal balance. This measurement will be used for HRV analysis.

The Movement disorder society-unified Parkinson's disease rating scale (MDS-UPDRS) Part III will be administered at baseline and 26 weeks after study medication titration. Each item of the MDS-UPDRS has a possible rating from 0 to 4, where 0 = normal, 1 = slight, 2 = mild, 3 = moderate, and 4 = severe.Clinical scales will be performed without (OFF) medication in those subjects that might be receiving dopaminergic drugs

The NMSS measures non-motor symptoms over the previous month. Each symptom is scored with respect to: Severity: 0 = None, 1 = Mild; 2 = Moderate; 3 = Severe and Frequency: 1 = Rarely (<1/wk); 2 = Often (1/wk); 3 = Frequent (several times per week); 4 = Very Frequent (daily or all the time).

The SCOPA-AUT was developed to evaluate autonomic symptoms in patients with Parkinson's disease. The scale is self-completed by patients and consists of 25 items assessing the following domains: gastrointestinal (7), urinary (6), cardiovascular (3), thermoregulatory (4), pupillomotor (1), and sexual (2 items for men and 2 items for women).

The RBDSQ is a 10-item, patient self-rating instrument assessing the subject's sleep behavior with short questions that have to be answered by either "yes" or "no" that address frequency and content of dreams, their relationship to nocturnal movements/behavior, injuries of the bed partner, nocturnal vocalization, etc. The maximum total score of the RBDSQ is 13 points.

University of Pennsylvania Smell Identification Test (UPSIT) changes.

Functional constipation will be assessed at screening and at 26 weeks after study medication titration using a questionnaire based on modified The Rome III Criteria for Functional Digestive Disorders (ROME III diagnostic criteria), which focuses on symptoms including straining, lumpy or hard stools, sensation of incomplete evacuation, sensation of anorectal obstruction or blockage, manual maneuvers to facilitate evacuation, and two or fewer bowel movements per week. This questionnaire is based on a six item self-report measures with a three point summated rating scale. The total score has a range of 0 to 12, with scores > 4 identifying functional constipation.

Color vision changes will be assessed using HRR pseudoisochromatic Plates.

Measures of insulin sensitivity in neuronal-origin enriched plasma extracellular vesicles EVs (central IR) will be used to test the association of changes in such sensitivity to changes in MIBG uptake and clinical scores. For that purpose, plasma samples will be collected and stored and -80oC (celsius degrees) to allow for isolation of neuronal origin EVs at the completion of the study.

This outcome will be measured by the content of neuromelanin, a product of catecholamine metabolism in locus coeruleus (LC) and substantia nigra (SN).

These measurements will be aggregated to calculate the correlation between changes in neuromelanin content as measured by NM-MRI and dopamine content as measured by DAT scan

Beat-to-beat intervals will be registered to assess sympatho-vagal balance. This measurement will be used for HRV analysis.

Peripheral IR will be defined by the homeostasis model assessment of IR (HOMA-IR) defined as fasting glucose (mmol/L) x fasting insulin (mU/mL)/22.5. A cutoff HOMA index of 2.0, equivalent to <50% sensitivity, will be used to define IR. Subjects will be considered to have IR if they either have a HOMA≥2.0 and/or HbA1c≥5.7