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.