Pathophysiologic significance of free and conjugated dopamines in congestive heart failure.

sulfoconjugated dopamine constitutes the major portion of circulating or excreted dopamine, but its physiologic significance is still unknown. To test whether conjugated dopamine serves as a source of free dopamine in response to acute stress, plasma concentrations of free and conjugated dopamine were measured during an acute exacerbation of heart failure. The plasma concentration of conjugated dopamine decreased significantly during the acute phase of heart failure, whereas that of free dopamine increased. The plasma concentration of free dopamine decreased, whereas the concentration of conjugated dopamine increased as heart failure improved. An infusion of dopamine increased the plasma concentration of conjugated dopamine, suggesting that at least part of the excess active dopamine was detoxified through conjugation. The results of these tests with both conjugated and free dopamine are interconvertible and indicate that conjugated dopamine can serve as a reservoir of active dopamine.