Renal handling of sodium, potassium, calcium and phosphate by medulla

The role of renal papilla on solute excretion was studied in rats having one papillectomized kidney (PTX) and one partially nephrectomized kidney with intact papilla (PTN). Glomerular filtration rate (GFR) was similar between the PTX kidney (0.14 +/- 0.01 ml/min/100 g) and PTN kidney (0.16 +/- 0.03 ml/min/100 g). Urinary Na excretion (UNaV = 1.03 +/- 0.36 mu Eq/min) and fractional Na excretion (FENa = 1.72 +/- 0.56%) of PTX kidney were nearly 10-fold greater than those of PTN kidney, respectively (UNaV = 0.11 +/- 0.04, p less than 0.03; FENa = 0.19 +/- 0.05, p less than 0.02) during hydropenia. After 5% saline expansion GFR of PTX kidney (0.23 +/- 0.03 ml/min/100 g) and PTN kidney (0.25 +/- 0.05 ml/min/100 g) were increased significantly. Na excretion was greatly increased in both kidneys; however, PTX kidney still excreted nearly 4-fold more Na than the PTN kidney. Ca and P excretions were not different between the PTX kidney and PTN kidney. Neither was K excretion different between the two kidneys during hydropenia or after KCl infusion. The results indicate that renal papilla does not regulate Ca, P and K excretions in the presence of moderate reduction of GFR; however, it plays an important role in the final excretion of urinary Na.