The neuroendocrine system and aging.

The course of aging in most endocrine glands is moderately well documented in man, but is somewhat less understood in the rat. With increasing age in man there is a significant decline in the secretion of hormones by the thyroid, adrenal cortex, testis and ovary; pituitary growth hormone falls but gonadotrophins rise. In man decline in the secretion of testicular and ovarian steroids appears to be due to primary age changes in the gonads, whereas in the rat age changes in the central regulatory mechanisms appear to be responsible for gonadal aging. Such findings have led to the formulation of a number of neuroendocrine theories of aging, which explain peripheral aging on the basis of an aging clock in the brain, primary age changes in neurotransmitter metabolism, age changes in the hypothalamus, pituitary and thyroid, or in the regulatory actions of these glands.