Urinary concentrating ability in early experimental pyelonephritis.

The effect of early bilateral pyelonephritis on urinary concentrating ability was studied in rats injected intravenously with enterococci or Staphylococcus aureus and in rats inoculated with Escherichia coli into the medullae of both kidneys. The mean maximum urinary osmolality of normal rats was 2352 mOsm/kg of water. Inoculation of E. coli caused reversible pyelonephritis with sterilization of the kidneys within 12 wk. By 1 day after injection the mean maximum urinary osmolality had decreased to about 1100 mOsm. remained at this level for 3 wk, and then rose to normal by 12 wk. After injection of enterococci and staphylococci, the mean maximum urine osmolality decreased over 3-4 days to about 1000 and 800 mOsm respectively. In the enterococcal infection (which is chronic) the maximum urine osmolality remained about 1200 mOsm for at least 12 wk whereas in the staphylococcal infection (which is reversible) the osmolality gradually rose. Antimicrobial therapy of E. coli renal infection with colistimethate sodium and S. aureus infection with ampicillin rapidly reduced bacterial titers in the kidneys with an associated rise in maximum urinary osmolality. Therapy of enterococcal renal infection with ampicillin produced less impressive decreases in bacterial titers in the kidneys and little or no improvement in urinary concentrating ability. With antimicrobial therapy or with the self-limited infections, the rate of increase in concentrating ability was directly correlated with the rate of decrease of bacterial titers. However, there was poor correlation between histological findings in the kidneys and urinary concentrating ability. These studies demonstrate that early experimental pyelonephritis is associated with a concentrating defect that can be rapidly reversed and therefore is not related to permanent renal damage.