Renal dopaminergic system activity in the rat remnant kidney.

BACKGROUND Renal dopamine exerts natriuretic and diuretic effects by activating D1-like receptors. Uninephrectomy results in increased renal dopaminergic activity and dopamine-sensitive enhanced natriuresis. METHODS The present study evaluated renal adaptations in sodium handling and the role of dopamine in rats submitted to (3/4) nephrectomy: right nephrectomy and excision of both poles of the left kidney ((3/4)nx rats). RESULTS Two weeks after surgery the absolute urinary levels of dopamine were markedly reduced in (3/4)nx rats whereas the urinary dopamine excretion per % of residual nephrons was significantly increased in the remnant kidney of (3/4)nx rats. The V(max) values for renal aromatic L-amino acid decarboxylase, the enzyme responsible for the synthesis of renal dopamine, were decreased in (3/4)nx rats. Renal catechol-O-methyltransferase activity, the enzyme responsible for the methylation of dopamine, was increased in (3/4)nx rats whereas the renal activities of monoamine oxidases A and B did not differ between (3/4)nx and Sham animals. Volume expansion (5% body weight) resulted in similar natriuretic responses in (3/4)nx and Sham rats. During D1 antagonist administration (Sch-23390, 30 microg x h(-1) x kg(-1)) the natriuretic response to volume expansion was reduced in (3/4)nx rats more pronouncedly than in Sham animals. CONCLUSION The decrease in absolute renal dopamine output in (3/4)nx rats is related with reduced renal synthesis and enhanced O-methylation of the amine. However, this is accompanied in (3/4)nx rats by increased renal dopamine excretion per residual nephrons and dopamine-sensitive enhanced natriuresis.