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Renal citrate metabolism and urinary citrate excretion in the infant rat

J Z Melnick1, P A Preisig, R J Alpern

  • 1Department of Pediatrics, Northwestern University Medical School, Chicago, Illinois, USA. j-melnick@nwu.edu

Kidney International
|March 18, 2000
PubMed

Insights

Infant rats exhibit higher urinary citrate excretion than adults, despite similar tissue citrate levels. This difference is linked to developmental changes in the kidney

Area of Science:

  • Nephrology
  • Pediatric Nephrology
  • Biochemistry

Background:

  • Hypercalciuria is common in both children and adults.
  • Children rarely develop kidney stones despite similar hypercalciuria prevalence.
  • Infants may have higher urinary citrate excretion than adults, potentially explaining reduced stone formation.

Purpose of the Study:

  • To investigate renal citrate excretion in infant versus adult rats.
  • To examine renal cortical citrate metabolism differences between infant and adult rats.

Main Methods:

  • Adult and infant male rats were housed in metabolic cages and fed synthetic diets.
  • Urine was collected, and renal cortical citrate metabolism was assayed.
  • Key enzyme activities and transporter functions related to citrate metabolism were assessed.

Main Results:

  • Infant rats showed significantly higher urinary citrate excretion (fourfold higher citrate:creatinine ratio and twofold higher concentration).
  • Plasma bicarbonate was lower and plasma potassium was higher in infant rats.
  • Despite higher urinary citrate, renal cortical citrate concentrations were comparable, and mitochondrial aconitase activity was lower in infants.

Conclusions:

  • Infant rats excrete more citrate in urine than adults, but this doesn't correlate with tissue citrate levels.
  • The increased urinary citrate in infants is likely due to developmental differences in proximal tubule citrate transport, independent of Na/citrate cotransport.
  • Further research into maturational changes in renal citrate handling is warranted.
Abstract

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