Effects of high salt intake on dopamine production in rat kidney

To examine the origin of increased urinary dopamine excretion (U(DA)V) during high salt intake, we measured U(DA)V from the innervated (INN) or the chronically denervated (DEN) kidney in rats fed either a high-salt (HS) or low-salt (LS) diet. U(DA)V of DEN [3.50 ± 0.46 ng· min^-1·inulin clearance (C(IN))^-1] and INN (4.00 ± 0.59 ng· min^-1·C(IN)^-1) kidneys in the HS group showed a significant increase compared with that of the respective kidney in the LS group (DEN 1.42 ± 0.12, INN 1.44 ± 0.09 ng·min^-1·C(IN)^-1), whereas the effect of denervation on U(DA)V was not significantly different between two groups. We determined aromatic L-amino acid decarboxylase (L-AADC) activity and dopamine degradation rate of microdissected proximal convoluted tubules to study the changes in dopamine metabolism. L-AADC activity in the HS group showed a significant increase compared with that in the LS group, although there was no significant change in dopamine degradation rate. We conclude that the increase in U(DA)V during high salt intake was mainly caused by the enhancement of extraneural dopamine production by the kidney in rats. Dopamine-producing enzyme, but not its degradation in the tubular cells, plays a role in the regulation of extraneural dopamine production.