Regulation of endothelin-converting enzyme 1 in nephrotic syndrome in rats

Nephrotic syndrome is characterized by severe proteinuria and sodium and water retention. Although endothelin (ET) 1 can cause natriuresis or antinatriuresis, the role played by ET-1 in proteinuria and in sodium retention due to nephrotic syndrome remains unclear.

We investigated the role played by the ET-1 system in sodium and water retention and in proteinuria in puromycin aminonucleoside induced nephrotic syndrome in rats using microdissected nephron segments, competitive polymerase chain reaction, and Western blot.

The expression of prepro ET-1, ET-converting enzyme 1 (ECE-1), and ET A receptor mRNAs, but not ET B receptor mRNA, in the glomeruli was increased in rats with nephrotic syndrome. The cGMP generation in the glomeruli induced by atrial natriuretic peptide and ET-1 was decreased, whereas the ET-3-induced cGMP generation was increased in rats with nephrotic syndrome. ECE-1 mRNA expression was increased not only in the glomeruli, but also in the thick ascending limbs and collecting ducts. The protein expression of ECE-1 was increased in the membrane fraction of the cortex and in the outer and the inner medulla of nephrotic rats. Blockade of ET A and B receptors by bosentan did not inhibit the occurrence of nephrotic syndrome. However, the administration of bosentan increased the urinary sodium excretion.

These data suggest that an activated ET-1-ET A receptor pathway in glomeruli and/or an increased ECE-1 mRNA expression in distal segments may participate in sodium and water retention, but not in the occurrence of nephrotic syndrome.