Effect of Estradiol+Drospirenone Versus Estradiol+MPA on Endothelial Function

Inclusion Criteria: 1. Healthy female postmenopausal volunteers, as defined by absence of menses for at least 12 months and follicle stimulating hormone (FSH) 30 IU/L; 2. Age 45 to 75 years; 3. Systolic blood pressure \<140 and \>90 mmHg and diastolic blood pressure \<90 and \>60 mmHg at the screening visit; 4. No personal history of diabetes; 5. Body mass index \< 30 kg/m2; 6. No clinically significant abnormalities on screening tests (complete blood count, serum electrolytes, liver enzymes, thyroid stimulating hormone, urinalysis, and electrocardiogram). Exclusion Criteria: 1. Current smoking, defined as smoking within the 12 months before the screening visit; 2. Alcohol intake \>1 beverage per night or history of alcohol abuse; 3. Current or past recreational drug use; 4. Personal history of hypertension, cardiovascular disease (coronary artery disease, congestive heart failure, valvular heart disease, stroke, transient ischemic attack, or intermittent claudication), hyperlipidemia, diabetes (defined as a fasting glucose ≥126 mg/dL), kidney disease, liver disease, venous or arterial thromboembolic disease, adrenal insufficiency, depression, or illness requiring overnight hospitalization in the past 6 months; 5. Risk factors for arterial or venous thromboembolism; 6. Personal history of breast cancer or any other type of cancer; 7. Personal history of endometrial hyperplasia, endometrial cancer, or unexplained vaginal bleeding; 8. History of cervical cancer or abnormal pap smear 9. Prescription or herbal medication use, excluding thyroid hormone supplementation; 10. Ischemic changes on resting electrocardiogram; 11. Serum creatinine ≥ 1.3 mg/dL. 12. Serum potassium level \> 5.0 mmol/L; 13. Known hypersensitivity to any of the study drugs; 14. Other active medical problems detected by examination or laboratory testing, except for treated hypothyroidism. 15. Pregnancy