Dietary ammonium chloride for the acidification of mouse urine.

A novel therapeutic compound was found to induce bladder tumors in male rats. Given the location of the tumors and the increased amounts of calcium- and magnesium-containing solids found in the urine of treated animals, we hypothesized that tumorigenesis was secondary to urine crystal formation rather than a direct effect of the drug on urothelium. To investigate the basis for the response, a method of acidifying rodent urine was needed. This study tested the efficacy of 1% dietary NH4Cl in reducing the urinary pH of male mice. After 1 wk, urinary pH (mean ± SD) at 1 h after light onset was 7.51 ± 0.32 among controls compared with 6.21 ± 0.31 for the NH4Cl-fed group. After 2 wk of supplementation, urinary pH was 7.78 ± 0.41 for controls and 6.20 ± 0.30 for the NH4Cl-fed group. To investigate whether the time of collection altered urinary pH, samples also were collected 8 h after the start of the light cycle on the day of the 2-wk collection. Urinary pH was 7.12 ± 0.28 for the control group and 5.80 ± 0.23 for the NH4Cl-fed mice. The pH differences between control and NH4Cl-fed groups and the differences in pH within groups at 1 and 8 h were statistically significant. Dietary NH4Cl is an effective urinary acidifier for mice. When evaluating the pH of mouse urine, care should be taken to compare samples collected at the same time after the start of the light cycle.