Effect of aging and endurance training on tissue catecholamine response to strenuous exercise in Fischer 344 rats

The purpose of the present investigation was to determine the catecholamine response in various tissues to a bout of strenuous exercise in young, adult, and old Fischer 344 rats. Further, to study the effect of endurance training on this response, animals from each age group underwent ten weeks of treadmill running at 75% of their functional capacity. On completion of the training program, all animals demonstrated significant increases (P less than 0.05) in VO2max and endurance capacity. At rest or immediately after an acute bout of strenuous exercise, animals were killed, and the heart, liver, kidney, and adrenals were removed for subsequent catecholamine analysis. Resting cardiac catecholamine levels declined significantly with age. In response to an acute exercise bout, epinephrine (E) levels in the heart were greatly reduced with age averaging 141.8, 62.3, and 21.7 ng/g for the 6-, 15-, and 27-month-old untrained group, respectively. The 15- and 27-month-old trained animals demonstrated significantly higher E levels (33% and 91%) than controls. A similar trend was found for norepinephrine (NE) content in the heart in response to acute exercise, with a marked reduction occurring with advancing age (904.6, 580.1, and 400.8 ng/g heart for 6-, 15-, and 27-month-old untrained groups, respectively). Again, training induced a greater NE response in the older trained animals compared to age-matched controls. In contrast, adrenal catecholamine levels showed a tendency to increase with age. It was concluded that when challenged with strenuous physical stress, cardiac catecholamine content is markedly diminished with age. Further, ten weeks of endurance training can attenuate this functional decline.