What stimulates atrial natriuretic factor release during exercise?

Prior studies have shown that circulating atrial natriuretic factor (ANF) increases during short-term exercise, but the mechanism controlling ANF release, as well as the effect of exercise training on ANF release, remains unclear. Fifteen healthy mongrel dogs underwent short-term exercise testing before and after a 12-week period of exercise training (n = 8) or cage confinement (n = 7). ANF, norepinephrine, epinephrine, right atrial pressure, and heart rate were measured simultaneously at rest and during exercise at the time of each acute exercise study. Data were analyzed for all animals with normal baseline ANF values. Exercise training had no modulating effect on circulating ANF levels at rest or during exercise. Therefore, data before and after exercise training or cage confinement were grouped (n = 24) to determine the effects of short-term exercise. ANF levels increased from 49 +/- 2 pg/ml at rest to 60 +/- 4 pg/ml during exercise (p less than 0.05). Heart rate, norepinephrine, and epinephrine values also increased, but right atrial pressure actually decreased from 2.3 +/- 0.9 mm Hg at rest to -3.8 +/- 0.9 mm Hg during exercise (p less than 0.05). There was no correlation between ANF concentrations and levels of these other variables either at rest of during exercise. By demonstrating an increase in ANF with a simultaneous decrease in right atrial pressure, this study clearly shows that increased right atrial pressure is not the secretory stimulus for ANF release during exercise in the normal dog. The lack of correlation between ANF and right atrial pressure, heart rate, norepinephrine, and epinephrine levels suggests that factors other than these variables stimulate ANF release during short-term exercise.