Cardiac noradrenaline turnover and urinary catecholamine excretion in trained and untrained rats during rest and exercise.

Abstract

AbstractRats were trained by daily swimming (1—2 h) during 15 weeks. The training caused a significant increase in heart weight. Cardiac noradrenaline (NA) and adrenal catecholamine (CA) contents were significantly increased in trained animals. When exposed to acute prolonged exercise the endogenous levels of cardiac NA decreased in untrained, but not in trained, rats. Resting cardiac NA turnover, as measured by rate of disappearance of exogenous 3H‐NA, was slower in trained than in untrained rats (T1/2= 52 h and 20 h, respectively). The NA turnover increased during exercise, but still remained slower in trained rats. Figures were obtained indicating a significantly lower initial uptake of exogenous NA in the hearts of trained rats. Resting excretion of CA in the urine was not different in trained and untrained rats, while the increase seen after a period of exercise was much greater in the untrained animals. The results indicate that chronic physical training induces a functional adaptation of the sympathicoadrenal system leading to a better transmitter economy during exercise. The nature of this adaptation remains, however, unsettled.