Postmenopausal Women Estrogen and Progesterone Infusion

The purpose of the study is to study the effects of aging, estrogen and progesterone on the brain. Specifically, we want to look at how the hypothalamus and pituitary (two small glands in the brain) respond to estrogen. The pituitary gland is controlled by the hypothalamus. The hypothalamus secretes GnRH (Gonadotropin-Releasing Hormone) that signals the pituitary to secrete the reproductive hormones, LH (Luteinizing Hormone) and FSH (Follicle Stimulating Hormone). These hormones act on the ovaries and signal the ovaries to produce estrogen and progesterone. Estrogen in the bloodstream then acts on the brain to modulate this system with changes in LH and FSH. Early changes associated with low levels of estrogen are inhibitory (estrogen negative feedback) while higher levels of estrogen (such as those present when a follicle in the ovary is ready to ovulate) stimulate LH to cause ovulation (positive feedback). This study will determine: 1) hypothalamic and pituitary levels of glucose uptake (as a measure of brain metabolic activity) at baseline and in association with estrogen negative feedback on LH (24 hr) and estrogen positive feedback on LH (72 hr); and 2) the effect of aging on estrogen feedback on LH, assessing negative feedback (nadir \~ 24 hr) and positive feedback (peak between 72 and 96 hr).

The transition to menopause is characterized by a decline in the numbers of functional ovarian follicles followed by a decrease in levels of inhibin A and B and complex changes in estradiol, which include an initial increase followed by an inevitable decrease. Therefore, there are dynamic changes in the hypothalamic-pituitary feedback from the aging ovary, prior to the ultimate loss of feedback that occurs with the complete cessation of ovarian function. While there is ample evidence that the loss of ovarian function is a major contributor to the menopause, there is evidence from animal models that primary age-related neuroendocrine changes may also contribute to reproductive aging. Specifically, there is evidence for changes in the hypothalamic and pituitary responses to estrogen negative and positive feedback. An understanding of the age-related changes in the physiology of the hypothalamic and pituitary responsiveness to gonadal steroid feedback is critical in determining whether hypothalamic and pituitary changes per se contribute to the menopause and the impact of the loss of reproductive function on the brain.

Eligibility Criteria:
Inclusion criteria:

postmenopausal women young (age 45-55) or old (age 70-80) History of natural menopause defined by the absence of menses for at least 12 months (or history of surgical menopause defined as bilateral oophorectomy) Normal TSH, PRL and CBC, and Factor V activity Normal BUN and Creatinine (\< 2 times the upper limit of normal) BMI between 18 to 30 kg/m2 An increased FSH measured at the screening visit will be consistent with menopause. If the initial determination is low, a repeat sample may be drawn.

Exclusion criteria:

Hormonal medication or herbal supplements and/or over the counter menopause therapy in the 2 months prior to study Any absolute contraindications to the use of physiologic replacement doses of estrogen and/or progesterone History of coronary artery disease Medications thought to act centrally on the GnRH pulse generator History of breast cancer or blood clots Smoking more than 10 cigarettes/day Prior history of allergic reaction to any dyes used with x-rays or scans and/ or any other contraindications to PET scans No metal implants, pacemakers, aneurysm clips, implanted hearing aids and/or any other contraindications to MRI scan