[Sympathetic regulation of adrenal medullary function during aging]

Our recent studies on changes in sympathoadrenal medullary function with age in anesthetized Wistar rats were reviewed. Although secretion rates of adrenaline and noradrenaline from the adrenal gland under resting conditions varied among animals, they gradually increased after 300 days and reached a level 2-4 times higher at 800-900 days compared with that of 100 days. Spontaneous activity of a single sympathetic nerve fiber under resting conditions also increased during aging in a manner similar to the catecholamine secretion rates. Reflex responses of mass activity of adrenal sympathetic nerve fibers to stimulation of baroreceptor and cutaneous mechanoreceptors were compared in young adult (4 months old) and aged (26 months old) Wistar rats under strictly controlled conditions for anesthesia, respiration and body temperature. Under these conditions the reflex depression in response to baroreceptor stimulation and cutaneous brushing as well as reflex excitation in response to cutaneous pinching were quite well maintained in the aged rats.