Inclusion Criteria:

• ≥ 18 years of age
• A diagnosis of resistant hypertension, defined as failure of concomitant use of 3 or more different anti-hypertensive agents including a diuretic to lower systolic blood pressure (SBP) to <140/90 mmHg or <130 mmHg for diabetics. Sitting blood pressure (BP) average at Screening must be ≥ 140 mmHg for non-diabetics or ≥ 130 mmHg for diabetics.
• A stable anti-hypertensive regimen at full or therapeutic doses for at least 30 days prior to Baseline. If any compound in the subject's anti-hypertensive therapy is considered to be at a therapeutic dose, it must be supported with documentation of the rationale for not increasing the compound's maximum prescribed dose.
• Females of childbearing potential must be using two forms of medically acceptable contraception (at least one barrier method) and have a negative pregnancy test at Screening and monthly thereafter. Women who are surgically sterile or those who are post-menopausal for at least 2 years are not considered to be of childbearing potential.
• Signed, written informed consent.

Exclusion Criteria:

• Sustained blood pressure of ≥ 180/120 mmHg
• Anticipated need for anti-hypertensive regimen adjustment during the length of the trial
• Planned weight loss, dietary program adjustment or initiation of an exercise program during the course of the study
• Required use of thigh cuffs for accurate blood pressure readings
• A diagnosis of acute or chronic liver disease including hepatitis B (with evidence of recent infection and/or active virus replication) and hepatitis C
• Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) > the upper limit of normal
• Chronic renal insufficiency, defined by an estimated glomerular filtration rate (GFR) < 30 ml per minute, or the requirement for dialysis
• Uncontrolled diabetes, defined by a Screening HgA1c > 9%
• Known syncopal disorder or orthostatic hypotension as defined by a ≥ 20 mmHg decrease in standing SBP as compared to sitting SBP at Screening or ≥ 10 mmHg decrease in standing DBP as compared to sitting DPB at Screening
• Occurrence of a cardiovascular event (myocardial infarction, stroke, transient ischemic attack, coronary or peripheral artery revascularization including coronary artery bypass grafting or angioplasty) within 6 months of Baseline
• A current diagnosis of heart failure
• Known to be positive for human immunodeficiency virus (HIV)
• Previous failure with an endothelin receptor antagonist due to safety or efficacy
• Chronic treatment with non-steroidal anti-inflammatory drugs (e.g., indomethacin, ibuprofen, piroxicam) or oral decongestants. As needed use of these medications, defined as treatment for no more than 3 consecutive days, is permitted.
• Treatment with any of the following medications: appetite suppressants containing vasoactive compounds (e.g., phenylpropanolamine HCl, ephedrine, pseudoephedrine, oxymetazoline HCl), warfarin, vitamin K antagonists, cholestyramine, rifampin, cyclosporine, erythropoietin, anabolic steroids, corticosteroids, tricyclic antidepressants (low doses up to 50 mg are permitted for sleep aide), recreational drugs or illicit substances
• Regular alcohol intake of greater than 14 units/week (a unit is defined as 12 ounces of beer, 4 ounces of wine, or 1 ounce of ≥ 50-proof hard liquor)
• Donation or significant loss of blood (greater than or equal to 480 mL) within 30 days or plasma within 14 days of Baseline
• Currently pregnant or breastfeeding
• Use of investigational agents within 30 days of Baseline
• Night shift worker