Increases in adrenal catecholamine secretion and adrenal sympathetic nerve unitary activities with aging in rats

Changes in sympathoadrenal medullary functions with age were investigated using urethane-chloralose anesthetized Wistar rats between about 100-900 days after birth. Although secretion rates of adrenaline and noradrenaline from the adrenal gland under resting conditions varied widely 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. Sympathetic nerve efferent unitary activity at resting conditions was also increased during aging in a manner similar to the catecholamine secretion rates.