Relation of Ammonia Excretion to Urine pH

The Effect of Buffer Loading Upon Ammonium Excretion in the Dog*

“…It therefore follows that the addition of large amounts of buffer to the tubular fluid and the associated acceleration of Na+-H+ exchange should not influence ammonium excretion. However, the results of these experiments are also compatible with the hypothesis that NH4+ gains access to the urine by an independent Na+-NH4+ exchange mechanism (9,16), and therefore do not provide critical information concerning the intimate nature of ammonium transport into the urine.…”

“…Although it is known that titratable acid excretion depends upon the amount of buffer in the urine and urine pH (2), and that ammonium excretion in man and dog is determined primarily by urine pH (3)(4)(5)(6), it is not clear whether there is any fundamental interdependence of these two moieties of acid excretion. In previous studies where both were measured (7)(8)(9)(10), variations in urine acidity could have affected either ammonium or titratable acid excretion predominantly and could thus have obscured a significant underlying relationship between the two.…”

The Mechanism of Ammonia Excretion During Ammonium Chloride Acidosis 1

“…The regression line was calculated from the data obtained in studies on rats receiving varying NH4C1 loads; the urine pH did not vary significantly among these groups. Rats whose urine pH was elevated, either by the administration of NaHCO3 or the injection and ingestion of 9 mg. of Diamox® every six hours (16), excreted far less ammonia than could be predicted from the level of glutaminase activity. The disproportionately low ammonia excretion in these rats may possibly be linked with the increased urine pH, which may have repressed some passive diffusion of NH3 out of the tubular cell.…”

“…However, since it has been demonstrated (17) Although the excellent correlation between anmonia excretion and glutaminase activity during NH-a1 loading strongly suggests that the rate of ammonia excretion is, in part, regulated by the rate of production of ammonia within the tubular cell, the manner in which the ammonia thus produced is transported into the tubular urine is not precisely clear. Two theories have been formulated: 1) Free molecular ammonia (NH,) may enter the tubular urine by a process of passive diffusion (4-8); 2) ammonium ions (NH++) within the tubular cell may be transported into the urine by an active process of ion exchange for tubular Na+ (16,21). These theories are illustrated in the two model cells of Figure 4.…”

Tissue and Renal Response to Chronic Respiratory Acidosis*

“…Particular care was taken to ascertain that each rat took the entire amount of diet offered. The intake of equal amounts of diet by both control and experimental animals is essential, for, as has been previously pointed out, variations in dietary intake result in altered excretion of acid by the kidneys (12). With respect to sodium, potassium and chloride, two different diets were used.…”