Effect of cyclosporine A on renal electrolyte transport: whole kidney and Henle loop study

We investigated whole kidney function and electrolyte transport in the loop of Henle of surface nephrons using micropuncture in rats pretreated for 5-7 days with cyclosporine A (CSA, 15 mg/kg). We also studied whether the kidney was able to increase K+ excretion acutely after a period of acute i.v. KCl loading (37 mumol/min.kg body weight). For Henle loop studies we microperfused the late proximal tubule downstream from an immobile wax block at two perfusion rates (15 and 40 nl/min). The fluid at the beginning distal tubule was collected and analyzed for inulin, Na+, K+, Cl-, Ca++, and Mg++. Plasma levels of CSA in our model ranged from 254 and 971 ng/ml and showed no relation to the obtained measurements. The pretreatment with CSA did not significantly change whole kidney or Henle loop electrolyte transport compared to drug free controls. Also, the CSA-pretreated rats were able to excrete an acute KCl load although this was at the expense of a marginally higher plasma K+ concentration and also a smaller urine flow increase during KCl loading. Thus CSA-pretreated rats showed only a mildly impaired response to KCl challenge in the absence of GFR impairment.