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.