Neuroendocrinology of aging in the male and female.

Many changes in the neuroendocrine axis occur with healthy normal aging in humans. Women cease ovarian follicle maturation and menstrual cycles entering the estrogen-deficient state termed menopause. Although not without risk, estrogen and progesterone replacement in postmenopausal women has been shown to ameliorate the complications of lowered estradiol concentrations, such as hot flushes and osteoporsis, while improving the risk of cardiovascular complications. Aging men have lowered serum free and total testosterone concentrations and may experience a less well defined symptom complex termed andropause. Both signs and symptoms of thyroid disease and interpretation of thyroid function tests are difficult in aging humans. Specifically, TSH secretion is diminished in aging so that suppressed serum TSH concentrations are indicative of but not specific for hyperthyroidism. Cortisol secretion is not altered in aging, although serum concentrations of DHEA-S are lower. Prolactin concentrations are increased in both men and women, with the increase being more pronounced in men. The clinical significance of this increase has not yet been determined. Finally, elderly humans are more likely to develop difficulties with fluid and electrolyte balance. Although some alterations in AVP secretion have been shown in the elderly, plasma concentrations are similar in young and elderly subjects. Other mechanisms, such as decreased glomerular filtration rate and a decreased sensitivity of the thirst mechanism in response to hypertonicity, may be important contributors to fluid and electrolyte imbalances.