Measurements of Tubular Fluid pH in vivo in Rats

Abstract

IN recently reported micropuncture experiments on the mechanism of urine acidification in the rat, pH of tubular fluid was measured after the fluid had been withdrawn from the nephron^1–4. A theoretical objection to this method is that carbonic acid may not be in equilibrium with carbon dioxide in the tubular lumen^5,6. Withdrawal of the fluid would allow the reaction CO₂ + H₂O ⇄ H₂CO₃ to reach equilibrium quickly with the result that both the concentration of carbonic acid and the pH would change. That this may be the case is suggested by recent estimates of tubular fluid pH in vivo by Rector, using a series of indicator dyes⁷. His results suggest a much greater degree of acidification in the proximal tubule than previously thought from in vitro measurements.