Changes in plasma free and conjugated noradrenaline levels during dynamic leg exercise in patients with mild congestive heart failure

We measured plasma levels of free and conjugated noradrenaline at the antecubital vein at rest in 127 patients with cardiac diseases with New York Heart Association functional classification (NYHA) class I and class II, and in 22 normal healthy subjects as the controls (C group). In 44 patients (NYHA class I: n = 22, class II: n = 22), the effect of mild dynamic leg exercise on plasma free and conjugated noradrenaline levels were investigated. In 18 patients (NYHA class I: n = 5, class II: n = 13), we measured plasma levels of free and conjugated noradrenaline at the antecubital vein and at the pulmonary artery simultaneously before and during exercise. Plasma noradrenaline levels were determined by high performance liquid chromatography coupled with trihydroxyindole fluorimetric detection. Plasma conjugated noradrenaline levels were measured as the plasma free form after deconjugation by heating the acidified sample at 100°C. Plasma free noradrenaline level was higher in NYHA class II group than in class I group or C group. On the other hand, there was a relationship in plasma conjugated noradrenaline level of NYHA class II group > NYHA class I group > C group. During dynamic leg exercise, plasma free noradrenaline level significantly increased in all three groups. The increment of plasma free noradrenaline was greater in NYHA class II than in NYHA class I group. Plasma conjugated noradrenaline decreased during exercise in NYHA class I and NYHA class II groups and the decrement of plasma conjugated noradrenaline was greater in NYHA class II group than in NYHA class I group. Plasma levels of free and conjugated noradrenaline returned to the resting values 15 min after the cessation of exercise. When the effects of dynamic exercise were compared between the antecubital vein and the pulmonary artery, the increment of the plasma free noradrenaline was greater in the pulmonary artery than in the antecubital vein and the decrement of the plasma conjugated noradrenaline was greater in the pulmonary artery than in the antecubital vein. These results suggest that conjugated noradrenaline is an indicator of chronic sympathetic nerve activation and may be used as pools for free noradrenaline in patients with mild congestive heart failure.