Short-term exercise has been associated with increased plasma levels of atrial natriuretic factor, a potent dilating and natriuretic hormone. In this study, the effect of exercise training on atrial natriuretic factor release during short-term exercise was investigated in men without a history of cardiovascular or other major disease. A well trained group of 10 men who exercised an average of 6,618 kcal/week was compared with a minimally trained group of 9 men who exercised 1,479 kcal/week. Maximal oxygen uptake was 55.2 ml/kg per min in the well trained group and 42.5 ml/kg per min in the minimally trained group (p < 0.05).
Plasma for atrial natriuretic factor, norepinephrine and epinephrine was obtained at rest, at 4 min of exercise and at maximal exercise. Atrial natriuretic factor was lower at rest in the minimally trained than in the well trained men (23 vs. 35.9 pg/ml, p < 0.05). At maximal exercise, atrial natriuretic factor increased 2.6 times the value at rest in minimally trained men (59.8 pg/ml, p < 0.05 vs. rest), but did not change in well trained men (34 pg/ml).
In minimally trained men at rest, at 4 min of exercise and at maximal exercise, plasma levels of atrial natriuretic factor correlated with heart rate, cardiac output, mean arterial pressure and plasma levels of norepinephrine and epinephrine; these correlations were not found in the well trained group.
Thus, short-term exercise results in a significant increase in atrial natriuretic factor in minimally trained but not in well trained men. This increase correlates with physiologic variables that reflect increased sympathetic activity in the minimally trained but not the well trained group. Thus, in well trained men there appears to be an increased stimulus for atrial natriuretic factor release at rest, but an uncoupling of the stimuli for its release during exercise.
