Bacterial Killing by Neutrophils in Hypertonic Environments

The effects ofhypertonic sodium chloride and urea solutions on the phagocytosis and killing of Escherichia coli by neutrophils were examined. Neutrophil function was progressively inhibited by increasing osmolarity, with sodium chloride more inhibitory than urea. However, neutrophils killed at 25 % of normal rates in 500 mosmol/L NaCI, and in 300 mosmol/L NaCI with 800 mosmol/L urea. These concentrations would rarely be exceeded in the human urinary tract. Inhibition of neutrophil superoxide production and degranulation was similar to that observed with phagocytosis and killing. Neutrophils also phagocytosed and killed E. coli in isotonic and hypertonic urine, but no improvement in function attributable to the uptake of urinary osmopro-tectants was evident. It is concluded that physiologic levels of sodium chloride and urea will slow, but not prevent, neutrophil activity at a hypertonic site of infection. Large numbers of neutrophils are found in the infected urinary tract, but their role in the elimination of microbial pathogens is unclear. The renal medulla and nascent urine are normally hypertonic, and in vitro studies have demon-strated that neutrophils have impaired activity in hypertoni