Renal handling of endogenous lithium in experimental diabetes mellitus in the rat.
1. The usefulness of determining the renal handling of endogenous lithium as a marker of proximal tubular sodium reabsorption was assessed in streptozotocin induced diabetes mellitus in the Sprague-Dawley rat. 2. The clearance and fractional excretion of lithium were determined before and following the development of diabetes mellitus, and compared with measurements of proximal tubular reabsorption made directly using micropuncture techniques. Endogenous lithium was measured in order to avoid the toxic tubular effects of exogenously administered lithium salts. 3. Although a trend existed for a reduction in the fractional excretion of lithium in diabetic animals (1.8 +/- 0.3 vs 2.4 +/- 0.5%; P greater than 0.20), this did not reach statistical significance and did not accurately reflect the change in directly measured tubular Na reabsorption. 4. The decrease in proximal tubular Na reabsorption demonstrated in diabetic animals treated with phlorizin was not significantly reflected in the fractional lithium excretion, although again a corresponding trend was evident (1.9 +/- 0.8 vs 0.6 +/- 0.2%; P greater than 0.10. 5. In summary, the significant alterations in tubular Na handling in diabetes mellitus, previously demonstrated directly using micropuncture techniques, are not reflected in the renal handling of endogenous lithium. This indirect method is inadequate to assess proximal tubular Na transport in experimental diabetes mellitus.
Pollock
C A
CA
Department of Medicine, University of Sydney, Concord Hospital, New South Wales, Australia.
Field
M J
MJ
D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008094:Lithium / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism
D008094:Lithium; D012964:Sodium