Free and conjugated plasma catecholamines in patients with congestive heart failure

Conjugation is an important mechanism in the deactivation process of circulating catecholamines, because most of the circulating catecholamines are found in the conjugated rather than the free form. To determine whether a defect in conjugation might account for some of the elevated free plasma norepinephrine in patients with CHF, we measured free and conjugated circulating catecholamines in 12 patients with chronic CHF. These measurements were also obtained in eight age-matched control subjects without clinical heart disease. The data demonstrate that the free plasma norepinephrine in patients with heart failure (566 ± 227 (SD) pg/ml) is significantly greater than the free plasma norepinephrine in normal age-matched control subjects (337 ± 148 pg/ml, p < 0.05). The amount of free circulating epinephrine in the patients with heart failure (51 ± 25 pg/ml) is similar to that in the control population (46 ± 50 pg/ml), whereas the free circulating dopamine content is greater in the heart failure population (36 ± 21 pg/ml) compared with normal (17 ± 15 pg/ml, p < 0.05). Although the absolute conjugated catecholamines are also increased in patients with heart failure, the percent conjugation of norepinephrine in heart failure (73%) did not vary from control values (71%). The percent conjugation of epinephrine in the group with heart failure (81%) was similar to that in the control group (76%), as was the percent conjugation of dopamine in the two groups (99%). Therefore, it is unlikely that a defect in conjugation of catecholamines is contributing to the excessive free plasma norepinephrine found in patients with congestive heart failure.