Ammonium chloride alters renal tubular cell growth and protein turnover

Since renal hypertrophy occurs in conditions associated with increased renal ammonia genesis it has been suggested that ammonia may stimulate renal growth. Indeed, quiescent cultured tubular epithelial cells exposed to NH4Cl undergo hypertrophy. However, ammonia inhibits liver regeneration in vivo and proliferation of cultured fibroblasts. This study was designed to evaluate the effect of ammonia (NH3/NH4+) as a regulator of kidney cell hypertrophy and also kidney cell proliferation.

Cultured opossum kidney cells and primary rabbit proximal tubular epithelial cells were grown with or without (controls) NH4Cl present.

After 3 days exposure to 5-20 mM NH4Cl, there was a dose-dependent depression of cell replication that ranged between 8 and 63% compared with controls (p < 0.017). In contrast, cell volume and protein content were significantly greater in the NH4Cl-treated cells. At 20 mM NH4Cl the protein content of treated cells exceeded that of controls by as much of 75%. This difference in protein content could, in part, be related to the disparity in cell density. However, experiments performed with cells at similar density revealed that NH4Cl also has a direct effect on cell protein content that increased by 25%; this appeared to be a consequence of depressed protein breakdown and was not due to altered protein synthesis. Experiments with rabbit kidney cells revealed that inhibition of replication was associated with a decrease in DNA [3H]thymidine incorporation. Cell cycle analysis revealed a fall in the proportion of cells in the S + G2 + M phase compared with controls (22 versus 30%, respectively; p < 0.01). NH4Cl also inhibited the burst of replication that followed chemically induced hypoxic injury of quiescent opossum kidney cells.

We conclude that in addition to inducing hypertrophy, NH4Cl can inhibit tubular cell proliferation. Thus, while heightened ammoniagenesis in vivo may favor hypertrophy, this in vitro study raises the question whether an elevated intrarenal ammonia content might be harmful when cell replication is required. Acute tubular necrosis is a condition in which elevated ammonia levels and a requirement for cell replication coexist and could serve as an important model to study this question.