This pilot study plans to learn more about the aging of blood vessels and arteries in women. As women age and go through menopause, their risk for cardiovascular disease increases. Also with aging and menopause, levels of the reproductive hormone estradiol decline. Hormone replacement therapy to restore estradiol levels does not protect women from cardiovascular disease, so lifestyle changes, such as regular exercise, are recommended to reduce disease risk. However, there are differences between men and women in their response to exercise. In older men, exercise improves the health of their arteries, but in postmenopausal women, exercise does not provide this benefit. The purpose of this pilot study is to determine whether low estradiol levels in postmenopausal women are responsible for the poor vascular response to exercise. In this study the investigators will also test whether treatment with resveratrol, a plant compound found in red wine, improves postmenopausal women's response to exercise. The investigators hypothesize that acute treatment with estrogen or resveratrol will improve vascular responses to an acute bout of exercise.