EFFECT OF INSULIN ON SODIUM-REABSORPTION IN HYPERTENSIVE PATIENTS

The effect of insulin on sodium reabsorption was studied with the hype rinsulinemic euglycemic clamp technique, using lithium clearance as a marker of sodium reabsorption in the proximal tubule. The subjects wer e 12 nondiabetic hypertensive patients who were divided into two group s. In the first group, the effect of insulin on sodium and lithium rea bsorption was examined. The second group served as a control. Blood gl ucose was continuously monitored from 9 AM to 10 AM (baseline period). Hyperinsulinemic euglycemic clamp was performed with an artificial en docrine pancreas by infusing insulin at a rate of 2 mU/kg min from 10 AM to noon. In the control group the protocol was exactly the same exc ept that glucose clamp was not performed. Urine was collected hourly f rom 9 AM to noon. In the glucose clamp group, urinary sodium excretion (UNaV) decreased by 42% during the second hour of the glucose clamp ( P < .02). Clearance of lithium (C-Li) and fractional distal sodium rea bsorption [(C-Li - C-Na)/C-Li] increased, and C-Na/C-Li decreased sign ificantly during the glucose clamp, In the control group, UNaV and (C- Li - C-Na)/ C-Li remained unchanged, and C-Li decreased significantly. As shown by the increase of C-Li and (C-Li - C-Na/C-Li, and the decre ase of UNaV and C-Na/C-Li in the glucose clamp group, insulin decrease s urinary sodium excretion by increasing distal sodium reabsorption, w hereas it inhibits sodium reabsorption in the proximal tubule.