The purpose of this study is to evaluate reproductive status in aged female rhesus macaques in order to further characterize the primate model for human menopause. While the occurrence of menopause has been documented in several nonhuman primate species, a longitudinal cohort study involving daily sampling, and hence, the detailed characterization of ovarian activity in menopausal and perimenopausal animals has not been conducted. The menstrual histories of 26 female rhesus macaques ages 20 years and older were examined for the 12 months prior to and including the 3-month study period. Each animal was categorized as either eumenorrheic, oligomenorrheic or amenorrheic based on average cycle lengths. Daily urine samples were collected from each animal for 12 weeks between November 8, 1994 - January 30, 1995, and the urine assayed via enzyme immunoassay for estrone conjugate (E1C) and pregnanediol-3-glucoronide (H-PdG). Hormone profiles for each animal were judged to be either ovulatory, questionably ovulatory, or senescent based on hormone concentrations within defined limits, patterned dynamics (e.g. H-PdG peaks immediately prior to observed menses), and follicular and luteal phase lengths within expected range. Each animal was then categorized as pre-, peri- or post-menopausal based on her menstrual history and hormone profile premenopausal animals were either eu- or oligomenorrheic, with ovulatory hormone profiles, peri-menopausal animals were either eu-, oligo-, or amenorrheic with questionable ovulatory hormone profiles, and post-menopausal animals were amenorrheic animals with senescent hormone profiles. Eleven animals (average age = 22.5 years) were pre-menopausal, 13 animals were peri-menopausal (average age =23.9 years), and two animals were post-menopausal (average age=29. years ). This study not only confirmed the occurrence of true menopause in a non-human primate species, but also characterized a perimenopausal state similar to the state in women. *KEY*Primate, Reproduction, Geriatric, Ovarian senescence, Hormone
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