Age and the endocrine system.

The pattern of age-induced changes in each endocrine system is unique. Both hormone levels and target organ responsivity are altered in the aging endocrine-cardiovascular system. Serum levels of vasopressor hormones both increase (norepinephrine) and decrease (renin, aldosterone). Target organ responses to beta-adrenergic stimulation in the heart and probably also in vascular smooth muscle decrease due to postreceptor changes. These effects contribute to the clinical problems of hypertension and orthostatic hypotension which characterize the elderly. Aging produces mild carbohydrate intolerance and a minimal increase in fasting serum glucose in healthy, nonobese individuals, primarily due to decreasing postreceptor responsiveness to insulin. Aging decreases the metabolism of thyroxine, including its conversion to triiodothyronine, but clinically significant alterations of thyroid hormone levels do not occur. Changes in the end-organ response to thyroid hormones, however, significantly alter the clinical presentation of thyroid diseases. Aging shifts the serum vasopressin-serum osmolality relationship toward higher serum vasopressin levels probably due to altered baroreceptor input, probably contributing to the tendency toward hyponatremia in the elderly. Aging slows the metabolism of cortisol, but glucocorticoid levels in the human are essentially unaltered by age. However, recent data indicate that delta-5 adrenal steroids decrease markedly in both men and women. Nodules in the anterior pituitary, the thyroid, and the adrenal increase in frequency with aging. Finally, the reproductive system is primarily altered by endocrine cell death, by unknown mechanisms, resulting in decreased estrogen and testosterone levels in women and men. This most obvious age-related endocrine change turns out to be incompletely understood and is not representative of most age-related endocrine changes. Despite characterization of these many age-related alterations in endocrine systems, therapeutic issues often remain unexplored, and more data are needed in many areas.