Distal nephron sodium handling by normal, nephrotic, pyelonephritic and partially nephrectomized rats

The renal tubular handling of sodium was evaluated in 10 normal (N), 9 edematous nephrotoxic serum nephrotic (Ne), 9 pyelonephritic (Py) and 12 partially nephrectomized (Nx) Wistar rats during maximal free-water clearance induced by intravenous infusion of hypotonic sodium chloride solutions. Fractional deliveries of sodium to distal nephron [(CH2O + CNa)/GFR%] were similar (P greater than 0.05) in N (23.2 +/- 0.69%), Ne (24.3 +/- 1.30%) and Nx (26.9 +/- 2.6%) rats. However, the fractional distal sodium reabsorption [CH2O/(CH2O + CNa)%] was significantly higher (P less than 0.05) in Ne (76.8 +/- 1.80%) and lower (P less than 0.05) in Nx (33.3 +/- 3.1%) rats when compared to normal rats (50.3 +/- 1.80%). Py rats exhibited a higher fractional delivery of sodium to distal nephron (33.5 +/- 3.4%) and a lower fractional distal sodium reabsorption (35.9 +/- 5.9%) when compared to normal rats (P less than 0.05). These data suggest that the distal nephron, by altering sodium reabsorption, contributes to the maintenance of sodium balance in Nx rats, whereas in Ne rats the distal nephron generates a positive sodium balance and edema. At very low glomerular filtration rates (GFR), as is the case for Py rats, sodium balance is maintained both by the proximal and distal portions of the nephron.