Effect of Fasting for Two Days on the Excretion of Ammonium in Dogs with Chronic Metabolic Acidosis

Background: The source of glutamine for renal ammonium production is ultimately dietary protein in the fed state and body proteins in fasting. Objective: Our objective was to determine if less NH+4 would be excreted by fasted dogs with chronic metabolic acidosis resulting in conservation of lean body mass. Methods: Acid-loaded fed and fasted dogs were given 10 mmol NH4Cl/kg for 5 days; the fasted group had food withheld on days 4 and 5. Results: The renal production of NH+4 was not significantly different in both acid-loaded groups, yet the rate of NH+4 excretion was significantly lower in the fasted dogs (8 vs. 21 mmol NH+4/mmol creatinine). The urine pH was significantly higher (6.0 versus 5.5) while titratable acid and the urine flow rate were significantly lower in these fasted dogs. Despite nearly equal urine flow rates and Na+ excretion rates after an infusion of saline, the fasted dogs failed to increase the rate of excretion of NH+4 to rates seen in the fed group. Conclusions: The lower rate of excretion of NH+4 in fasted, acidotic dogs appeared to be due to a lower distal H+ secretion. This may help preserve lean body mass during fasting.