Collecting duct is a site of sodium retention in PAN nephrosis: A rationale for amiloride therapy

Micropuncture studies of the distal nephron and measurements of Na,K-ATPase activity in microdissected collecting tubules have suggested that renal re tention of sodium in puromycin aminonucleoside (PAN) nephrotic rats origina tes in the collecting duct. The present study demonstrated this hypothesis by in vitro microperfusion and showed that amiloride was able to restore so dium balance. Indeed, isolated perfused cortical collecting ducts from PAN- treated rats exhibited an abnormally high transepithelial sodium reabsorpti on that was abolished by amiloride, and in vivo administration of amiloride fully prevented decreased urinary sodium excretion and positive sodium bal ance in nephrotic rats. As expected from the aldosterone independence of Na f retention in PAN nephrotic rats, blockade of aldosterone receptor by pota ssium canrenoate did not alter urinary Na+ excretion, Na+ balance, or ascit es formation in PAN nephrotic rats.