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Institute of Pharmacology and Therapeutics, Faculty of Medicine, 4200 Porto, Portugal
The present study evaluated renal and intestinal adaptations in
sodium handling in uninephrectomized (Unx) rats and the role of
dopamine. Two weeks after uninephrectomy, the remnant kidney in Unx
rats weighed 33 ± 2% more than the corresponding kidney in
sham-operated (Sham) animals. This was accompanied by increases in
urinary levels of dopamine and major metabolites
[3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid] and
increases in maximal velocity values (169 vs. 115 nmol · mg
protein
1 · 15 min1) for renal
aromatic L-amino acid decarboxylase, the enzyme responsible for the synthesis of renal dopamine. High salt (HS) intake increased (P < 0.05) the urinary excretion of dopamine and DOPAC
in Unx and Sham rats. However, the urinary levels of
L-3,4-dihydroxyphenylalanine, dopamine, and DOPAC in Sham
rats during HS intake were lower than in Unx rats. Blockade of dopamine
D1 receptors (Sch-23390, 2 × 30 µg/kg) reduced the
urinary excretion of sodium in Unx (31% decrease) more pronouncedly
than in Sham (19% decrease) rats. However, inhibition of renal
Na+-K+-ATPase activity by dopamine was of
similar magnitude in Unx and Sham rats. In parallel, it was observed
that uninephrectomy resulted in a significant reduction in jejunal
sodium absorption and Na+-K+-ATPase activity in
jejunal epithelial cells. In jejunal epithelial cells from Sham rats,
dopamine (1 µM) failed to inhibit
Na+-K+-ATPase activity, whereas in Unx rats it
produced a significant reduction. It is concluded that uninephrectomy
results in increased renal dopaminergic activity and dopamine-sensitive
enhanced natriuresis. Furthermore, it is suggested that decreased
jejunal absorption of sodium may take place in response to partial
renal ablation, as an example of renal-intestinal cross talk.
intestine; sodium-potassium-adenosine-5'-triphosphatase
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