Impact of Estradiol on Endothelial Function in Peri-Menopausal Women

Inclusion Criteria: * Peri-menopausal women between 40-58 years of age with variable cycles as defined by increase in cycle length of greater than 7 days within ten consecutive cycles, or amenorrhea for more than 2 months, but less than 12 months. Exclusion Criteria: * Women who are pregnant, planning on becoming pregnant, or are breast feeding; * Women who have a history of cardiovascular disease, blood clots (e.g, pulmonary embolism or deep vein thrombosis), stroke, cancer, or liver disease; * Women who have a body mass index less than 18 or greater than 35kg/m2; * Women who use tobacco products; * Women who's blood pressure is greater than 140/90 mmHg, have been diagnosed by a physician with hypertension or are taking medication for high blood pressure; * Women who have a neurological disease, or diabetes; * Women who have had a hysterectomy or have used hormones (birth control or hormone replacement) within the past 3 months; * Women who have a latex allergy.