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Renal dopaminergic system in nephrotic syndrome and after remission
Background:
Although intrarenal dopamine is known to behave as an endogenous natriuretic hormone the role of the renal dopaminergic system in the sodium handling of nephrotic oedema remains unknown.
Study Design:
We monitored the daily urinary excretion of free dopamine, L-DOPA-its precursor, and its metabolites, DOPAC and HVA, during sodium retention accompanying the nephrotic state and natriuresis leading to oedema mobilization in eight patients (mean age 8.0+/-2.4 years) with drug-induced remission of minimal-change nephrotic syndrome (MCNS).
Results:
During natriuresis the urinary levels of dopamine did not increase in parallel with sodium excretion in any of the eight patients studied. Moreover, after remission of the nephrotic syndrome the urinary levels of dopamine were significantly lower than during the nephrotic state (1565.3+/-361.7 vs 2416.1+/-558.4, P= 0.02). In contrast, the urinary excretion of L-DOPA increased markedly during natriuresis resulting from remission of proteinuria (from 87.0+/-40.5 up to 296.9+/-86.3 nmol/24 h; P< 0.01).
Conclusion:
We conclude that the natriuretic response resulting from drug-induced remission of proteinuria in MCNS is accompanied by a decrease in the renal uptake/decarboxylation of L-DOPA to dopamine.