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Lithium clearance during variations in sodium intake in man: effects of sodium restriction and amiloride
Author(s) -
BOER W. H.,
KOOMANS H. A.,
MEES E. J. DORHOUT,
GAILLARD C. A.,
RABELINK A. J.
Publication year - 1988
Publication title -
european journal of clinical investigation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.164
H-Index - 107
eISSN - 1365-2362
pISSN - 0014-2972
DOI - 10.1111/j.1365-2362.1988.tb01259.x
Subject(s) - amiloride , sodium , lithium (medication) , chemistry , reabsorption , nephron , medicine , endocrinology , renal sodium reabsorption , tubular fluid , excretion , renal function , biochemistry , organic chemistry
. Assuming that lithium is exclusively reabsorbed in the proximal tubules in proportion to sodium and water, the lithium clearance (C Li ) has been advanced as an index of filtrate delivery from the proximal tubules. However, studies in the rat and dog showed that C Li drops sharply at fractional sodium excretion rates (FE Li ) below 0·4% due to lithium reabsorption in the amiloride‐sensitive segment of the distal nephron, which disqualified C Li as an index of distal filtrate delivery during sodium restriction in these animals. In order to investigate whether this phenomenon also occurs in man, we studied C Li in 103 normal subjects at varying sodium intakes, including marked sodium restriction. In contrast to findings in the rat and dog, no sharp drop but a gradual fall in C Li was observed at decreasing FE Na values down to 0·02%. Maximum urine flow, another index of filtrate delivery from the proximal tubules, decreased proportionally, suggesting that the fall in C Li was due to enhanced proximal and not distal lithium reabsorption. Amiloride (15 mg p.o.) did not affect C Li despite unequivocal effects in the distal nephron in eight normal subjects at a mean FE Na of 0·1%. In conclusion, a low FE Na due to severe sodium restriction in man is not accompanied by strongly enhanced distal lithium reabsorption sensitive to amiloride. Thus, in contrast to the rat and dog, a low FE Na forms no objection to use C Li as an index of sodium and filtrate delivery from the proximal tubules in humans.