The effect of streptozotocin-induced diabetes mellitus on urinary excretion of sodium and renal Na+-K+-ATPase activity.

Renal sodium handling and microsomal Na+-K+-ATPase activity in kidney cortex, medulla and papilla of rats with streptozotocin-induced diabetes mellitus (DM) was studied. During 7 days following the administration of streptozotocin GFR, urinary excretion, filtered load and tubular reabsorption of Na+ averaged (mean +/- SE) 1.18 +/- 0.016 ml/min, 1.74 +/- 0.14, 177.3 +/- 8.9 and 175.6 +/- 8.9 mEq/min respectively in experimental rats as compared to corresponding rates of 0.85 +/- 0.04 (P less than 0.001), 0.85 +/- 0.03 (P less than 0.001), 129.8 +/- 5.8 (P less than 0.001) and 129 +/- 5.8 (P less than 0.001) respectively in the control rats. The activity of microsomal Na-K-ATPase in the kidney cortex, medulla and papilla of the control group was (mean +/- SE) 44.7 +/- 1.7, 150 +/- 7.5 and 37.4 +/- 3.6 (mumoles Pi/mg prot/h) respectively. 24 h after DM induction Na-K-ATPase activity in the cortex rose to 59.3 +/- 2.4 (P less than 0.001) and remained high after 3 and 7 days. Medullary Na-K-ATPase activity was unchanged 24 h after streptozotocin administration but was markedly increased to 260 +/- 9 (P less than 0.001) after 3 days and remained high after 7 days. These findings show that streptozotocin-induced DM in rats causes a substantial increase in GFR which is associated with a net increase in filtered and reabsorbed load of Na+ and natriuresis. These alterations are accompanied by a marked increase in Na-K-ATPase activity in renal medulla and in the cortex.