Sex Hormones and Orthostatic Tolerance

Inclusion Criteria: * Healthy, English-speaking non-smoking women age 18- 34 with regular menses Exclusion Criteria: * Gynecologic: 1. current or past estrogen-dependent neoplasia, 2. unexplained vaginal bleeding, 3. history of uterine fibroids, 4. current pregnancy, 5. known or suspected breast or uterine cancer, 6. partial or complete hysterectomy * Cardiac: 1. myocardial infarction, ventricle tachycardia or fibrillation, 2. angina, 3. valvular disease, 4. congestive heart failure, orthopnea, paroxysmal nocturnal dyspnea, 5. current arrhythmias, 6. prosthetic valves * Pulmonary: 1. current cigarette smokers, or pipe or cigar smokers, 2. chronic obstructive pulmonary disease, 3. adult asthma, 4. dyspnea on exertion, 5. current bronchitis, pneumonia, or tuberculosis, 6. lung carcinoma, 7. pulmonary embolus, recent * Vascular: 1. claudication or history of peripheral vascular disease, 2. abdominal or thoracic aortic aneurysm, or repair of same, 3. cerebral aneurysm, vascular malformations, 4. hypertension, systolic or diastolic, or strong family history of hypertension * Gastrointestinal: 1. GI malignancy, 2. hepatitis, current, 3. splenomegaly from any cause, 4. Cholecystitis, 5. current diverticulosis or diverticulitis, inflammatory bowel disease, ulcerative colitis, Crohn's Disease, 6. previous gastrointestinal surgery * Infectious Disease: any intercurrent infection * Hematologic/Oncologic: 1. receiving chemotherapy or radiation therapy, 2. any metastatic malignancy, 3. anemia (hematocrit \< 35), 4. thrombocytopenia or thrombocytosis, 5. neutropenia, 6. hematologic malignancy, 7. bleeding dyscrasia * Neurologic: 1. history of cerebral vascular accident with any neurologic sequels, 2. uncontrolled seizures (e.g. more than 1 seizure/year), 3. transient ischemic attacks, 4. dementia, 5. neurologic conditions producing dyscoordination, peripheral neuropathy, or myopathy, 6. severe migraine headaches * Endocrine: 1. diabetes mellitus, 2. any untreated endocrinopathy * Renal: 1. chronic renal disease, 2. any history of renal disease or impairment, 3. current urinary tract infection * Musculoskeletal: 1. inflammatory arthritis history (e.g., rheumatoid, psoriatic, Reiters), 2. any history of pathologic fractures, including vertebral compression fractures * Pharmacologic: 1. any illegal drug use, 2. alcohol use greater than an average of 4 oz/day over 30 days, 3. coumadin or heparin use, 4. current systemic antifungal use