To determine whether treatment with the ENaC inhibitor, amiloride, improves endothelial function and arterial stiffness in obese insulin resistant subjects in a randomized placebo-controlled trial examining pre and postmenopausal women and age-matched men.

Overweight/obese males, pre- and post-menopausal females with insulin resistance, 30-70 years of age will be recruited. Following screening, eligible men and women will be randomly assigned to either amiloride (max dose 5mg) or placebo in a double-blinded design manner.

After randomization, subjects will be scheduled for an outpatient visit to the undergo baseline assessment of arterial stiffness (carotid femoral pulse wave velocity - cfPWV) and endothelial function (brachial popliteal artery flow mediated dilation). Subject assessment will be repeated at 12 weeks and at 24 weeks.

Inclusion Criteria:

• 30 to 70 years of age at randomization
• Body mass index (BMI) 25.1-50 kg/m2 or waist circumference > 88 cm (> 35 in) in women and >102 cm (>40 in) in men. 3, 4
• One other characteristic of metabolic syndrome (elevated triglycerides ≥150 mg/dl; HDL cholesterol <40 mg/dl in men and <50 mg/dl in women; blood pressure ≥130/85 mm Hg or treatment for hypertension; impaired fasting glucose (≥100 mg/dl)) or fasting insulin level >10 mU/L (correlates with insulin resistance).

Exclusion Criteria:

1. History of type 1 or type 2 diabetes
2. Known cardiovascular events within the last 12 months (stroke, acute coronary event, revascularization, heart failure hospitalization).
3. History of uncontrolled thyroid disease, chronic liver disease (cirrhosis) or GFR <50 ml/min.
4. Use of potassium sparing medications (angiotensin II receptor blockers, angiotensin converting enzymes inhibitors or mineralocorticoid receptor blockers) or use of potassium supplements.
5. Active cancer (This criterion does not apply to those subjects with basal cell carcinoma or stage 1 squamous cell carcinoma of the skin)
6. Excessive alcohol consumption (>14 drinks/week for men, >7 drinks/week for women)
7. Current tobacco use
8. Non controlled hypertension
9. Participation in regular exercise > 3 days/wk per week at a moderate or vigorous intensity
10. Pregnancy or lactation in women (or women not using contraceptives)
11. Women who plan to become pregnant during the duration of the trial
12. Chronic use of NSAIDs
13. Potassium level > 5.0 mqE/L at time of screening
14. Blood pressure at screening <110/70

6 months