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Renal bicarbonate reabsorption and hydrogen ion excretion in normal infants

C M Edelmann1, J R Soriano, H Boichis

  • 1Department of Pediatrics, Albert Einstein College of Medicine-Bronx Municipal Hospital Center, Bronx, N. Y.

The Journal of Clinical Investigation
|August 1, 1967
PubMed

Insights

Infants can acidify urine similarly to older children, but have a lower bicarbonate threshold. This is likely due to differences in nephron function, not limited hydrogen excretion capacity.

Area of Science:

  • Pediatric Nephrology
  • Renal Physiology

Background:

  • Infants exhibit "physiologic acidosis," a state whose causes are not fully understood.
  • Previous research suggests potential renal limitations in hydrogen ion excretion or bicarbonate reabsorption.

Purpose of the Study:

  • To investigate the renal capacity for urine acidification and bicarbonate reabsorption in infants.
  • To determine the underlying mechanisms of "physiologic acidosis" in early life.

Main Methods:

  • Acute ammonium chloride administration to infants (1-16 months).
  • Urine acidification assessment, including titratable acid and ammonium excretion.
  • Bicarbonate titration studies to evaluate reabsorption thresholds and rates.
  • Analysis of glomerular filtration rate (GFR) to tubular reabsorptive capacity (TRC) ratios.

Main Results:

  • Infants demonstrated similar urine acidification capacity to older children, with comparable total hydrogen ion excretion.
  • Infants showed higher titratable acid and lower ammonium excretion rates.
  • Bicarbonate titration revealed a low renal plasma bicarbonate threshold (21.5-22.5 mmol/L) and significant titration splay.
  • Nephron heterogeneity, with a rightward skew in GFR/TRC ratios, indicated nephrons with reduced transport capacity.

Conclusions:

  • The "physiologic acidosis" of infancy is not due to limited renal hydrogen excretion or reduced bicarbonate reabsorption capacity.
  • A low renal plasma bicarbonate threshold, influenced by nephron functional and morphologic heterogeneity, is the primary cause.
  • This low threshold impacts bicarbonate reabsorption kinetics during infancy.

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