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Role of hypothalamic catecholamines in aging processes.

Defects that develop in the hypothalamic area of the brain are believed to initiate many declines in body functions in aging rats and mice. The decreases found in hypothalamic norepinephrine and dopamine are particularly important since they lead to reduced gonadotropic hormone secretin and cessation of estrous cycles in female rats and a decrease in testosterone secretion in male rats, lower GH and somatomedin (IGF-I) secretion and reduced protein synthesis, diminished thyroid hormone secretion and lower body metabolism, higher PRL secretion and development of numerous mammary and pituitary tumours, and reduced immune competence. The reduction in hypothalamic norepinephrine and dopamine activity is believed to be due to damage and loss of neurons owing to toxic products formed during metabolism of norepinephrine and dopamine; to the damaging effects to neurons produced by the chronic action of estrogen, PRL, and indirectly by adrenal glucocorticoids; and to changes in enzymes responsible for synthesis and metabolism of norepinephrine and dopamine. When old rats are given drugs that elevate norepinephrine and dopamine, most of the above and other decrements of aging are delayed or reversed, and length of lifespan may be prolonged. Decreases in hypothalamic norepinephrine and dopamine have also been reported in elderly human subjects, but it is unknown whether these are related to declines in body functions.