Neuroendocrine mechanisms and aging.

Evidence describing altered neuroendocrine function during aging from this and other laboratories is reviewed, with focus on changes in the brain-pituitary-ovarian-adrenal-hepatic and in the brain-pituitary-ovarian systems. Difficulties in interpreting the discordant data on age-related changes in pituitary function are discussed. Among mechanisms of reproductive aging are changes at both the ovarian and hypothalamic level (including reduced catecholamine levels, turnover, and synaptosomal uptake). However, it cannot yet be concluded that impairments of hypothalamic catecholamine metabolism are the primary cause for the loss of regular cycles. Evidence for dopaminergic impairments in the basal ganglions of humans and rodents during normal aging suggests that these changes may be a general phenomenon of aging. Although the origins of the changes are not yet known, neuronal cell loss in the substantia nigra would not seem to be the only cause.