Sex Hormones and Atherosclerosis Prevention in Perimenopausal Women

Inclusion Criteria: * Healthy women of all races and ethnic backgrounds in one of the following groups: * Premenopausal: 18-49 years, regular menstrual cycles with no change in observed cycle length (21-35 days) * Perimenopausal: 40-55 years, categorized as either early (at least 2 cycles with cycle length changes of at least 7 days) or late (more than 3 months of amenorrhea) transition * Postmenopausal: 45-70 years, more than 12 months of amenorrhea as defined by the menopausal staging system (STRAW); additionally, postmenopausal women will be categorized into early and late stages as defined by the STRAW definition, specifically, women who are less than 5 years postmenopause will be considered early, and women more than 6 years will be categorized as late * All postmenopausal women will have undergone natural menopause * No oral contraceptive or Hormone Replacement Therapy (HRT) use for at least 6 months * Resting blood pressure less than 140/90 mmHg * Plasma glucose concentrations less than 110 mg/dl under fasting conditions * Sedentary or recreationally active (less than 3 days of vigorous aerobic exercise) * No use of medications that might influence cardiovascular function * Nonsmokers * No use of vitamin supplements or willing to stop use for duration of the study Exclusion Criteria: * History of or active estrogen-dependent neoplasms, acute liver or gallbladder disease, vaginal bleeding, venous thromboembolism, hypertriglyceridemia, and cardiovascular disease * Known allergy to transdermal patch or GnRHant * Other contraindications to HRT and GnRHant