Enhanced fractional sodium reabsorption in the ischaemic kidney revisited with lithium as a probe.

Extraction of lithium and 51Cr-EDTA across each of the two kidneys was determined during renal vein catheterization in 14 hypertensive patients with unilateral or bilateral renovascular disease before and after i.v. injection of furosemide. Before the administration of furosemide an increased fractional lithium reabsorption was demonstrated across the affected, or more affected kidney. This difference was abolished by furosemide. Using lithium as a probe for sodium, our data suggest an increased fractional tubular sodium reabsorption in the ischaemic human kidney probably located to the proximal tubules as well as to the loop of Henle. Determination of single-kidney fractional lithium reabsorption holds promise as a new research tool for future evaluation of functional abnormalities during divided renal function studies.