UP-REGULATION OF ATRIAL-NATRIURETIC-PEPTIDE GENE-EXPRESSION IN REMNANT KIDNEY OF RATS WITH REDUCED RENAL MASS

Atrial natriuretic peptide (ANP) is synthesized in the kidney but its physiologic significance there is unclear. To determine whether renal expression of the ANP gene is regulated, renal ANP mRNA expression was assessed in remnant kidneys after 5/6 nephrectomy in Munich-Wistar ra ts. In normal sodium intake groups, ANP mRNA expression in the remnant kidney was significantly increased by 5.0 +/- 0.8-fold (n = 7, mean /- SEM) at 4 d when compared with sham-operated controls (n = 6, all s ham-operated groups) (P < 0.001 by Scheffe's test) and by 28.3 +/- 5. 1-fold at 14 d. This latter response was markedly diminished to 7.6 +/ - 2.1-fold (n = 7, versus sham) in rats maintained on a low sodium die t. At 4 d, on the other hand, no significant downregulation was observ ed with dietary sodium restriction. Because natriuretic peptides have previously been shown by us to play a major role in the adaptive respo nses of remnant nephrons to renal mass ablation, these data suggest th at ANP of renal origin may contribute to the overall mechanism for enh ancing sodium excretion in the face of declining nephron number.