The possible contribution of circulating dopamine sulfate to urinary free dopamine and the synthesis of norepinephrine by the renal nerves were examined in the isolated perfused rat kidney. Perfusion of the kidney with dopamine sulfate did not yield significant amounts of free dopamine indicating that, unlike L-dopa, dopamine sulfate is not a good source of urinary free dopamine. The excretion of dopamine sulfate was slower than or comparable with that of free dopamine, suggesting that sulfoconjugation is not a mechanism to facilitate the excretion of free dopamine. Unlike free dopamine, dopamine sulfate was not metabolized by renal catechol-O-methyltransferase or monoamine oxidase. Perfusion of L-dopa and free dopamine led to the generation of norepinephrine in the kidney. This synthesis was abolished when the kidney was denervated, suggesting that the renal nerves were the main sites of the norepinephrine synthesis. Both norepinephrine and dopamine were rapidly metabolized by catechol-O-methyltransferase and monoamine oxidase, but renal phenolsulfotransferase appeared to have no action on the catecholamines.
