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<0.001), 0.85±0.03 (P<0.001), 129.8±5.8 (P<0.001) and 129±5.8 (P<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 (moles Pi/mg prot/h) respectively. 24 h after DM induction Na–K-ATPase activity in the cortex rose to 59.3±2.4 (P<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<0.001) after 3 days and remained high after 7 days.These findings show that stretozotocin-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.This study was supported by the Morton S. Kaufman Hemodialysis Foundation and by the Joint Research Fund of the Hebrew University and Hadassah