Fluoride renal clearance: a pH-dependent event

Area of Science:

• Nephrology
• Renal Physiology
• Fluoride Toxicology

Background:

• Renal clearance of fluoride (CF) is crucial for understanding fluoride homeostasis.
• Previous research suggested urine flow rate and chloride clearance as primary determinants of CF.

Purpose of the Study:

• To investigate the determinants of renal fluoride clearance in rats.
• To elucidate the relationship between urinary pH and fluoride reabsorption.

Main Methods:

• Studied renal clearance of fluoride (CF) in pentobarbital-anesthetized rats.
• Manipulated urinary pH using NaHCO3, NH4Cl, acetazolamide, and mannitol.
• Assessed correlations between CF, urine flow rate, ion clearance, and urinary pH.

Main Results:

• Renal fluoride clearance (CF) was dissociated from urine flow rate and chloride clearance.
• CF showed a strong positive correlation with urinary pH.
• At pH 5.0, CF/GFR was <5%; at pH 7.6, CF/GFR exceeded 65%.

Conclusions:

• Tubular reabsorption of fluoride is inversely related to tubular fluid pH.
• Fluoride reabsorption occurs primarily via nonionic diffusion of hydrogen fluoride.
• Approximately 35-45% of filtered fluoride is reabsorbed in the proximal tubule, with distal nephron reabsorption increasing in acidosis.