URINARY ACIDIFICATION IN BILATERAL OBSTRUCTIVE UROPATHY

Studies on Urinary Acidification II

Abstract

In obstructive uropathy, the urinary acidifying function, which is one of the renal medulla functions, is generally reduced in the early phase. Therefore, clinically, acidosis appears frequently in cases with slight decrease of GFR.
To investigate the degree of reduction of urinary acidifying function in obstructive uropathy, the weak acids are examined by titration curve analysis.
The results are as follows
1) The circadian rhythm with wide range of daily urinary acid excretion was observed in normal control group, but patients with acidosis due to renal insufficiency by obstructive uropathy did not show this rhythm.
2) After oral administration of ammonium chloride, normal control group showed approximately a double increase of total acid excretion, from 62mEq/day to 119mEq/day. In this increase of total acid excretion, TA is about 25% and NH₄⁺ is about 75%.
3) Some patients with obstructive uropathy had decreased concentration ability even when the GFR was normal. The function of acid excretion in tubules, however, was intact in such cases. This result indicates that the function of acid excretion depends on the GFR, rather than the concentration ability in kidney.
4) In these cases, however, plasma total CO₂ ([CO₂] p) becomes much lower than in the normal control, and this acidosis stimulates the renal excretion of urinary weak acids. Therefore, to estimate the urinary acidifying function, the clearance index of H⁺(net H⁺/1/[CO₂] p) is more effective than the net acid excretion.