Conditions: Postmenopause Aging
Keywords: menopause estrogen progesterone hormone replacement aging PET
Allocation: NON_RANDOMIZED | Intervention model: PARALLEL
Enrollment: 20
Healthy volunteers: yes

Brief summary:
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).

Detailed description:
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.

Arms:
arm 1: Graded estradiol infusion to young postmenopausal women. Graded progesterone infusion to young postmenopausal women. arm 2: Graded estradiol infusion to young postmenopausal women. Graded progesterone infusion to young postmenopausal women..

Interventions: intervention 1: Estradiol infusion intervention 2: Progesterone infusion
Intervention descriptions: intervention 1: Graded estradiol infusion of 0.1 mcg/kg/hr for 12 hr, 0.135 mcg/kg/hr for 12 hr, 0.165 mcg/kg/hr for 12 hr and 0.2 mcg/kg/hr for 60 hr. intervention 2: Progesterone infusion of 4.77 nmol/kg/hr (1.5 mcg/kg/hr) for 24 hr and 6.36 nmol/kg/hr (2 mcg/kg/hr) for the final 24 hr of the 5-day study.

Protocol document: