Kidney pressures after the release of 24 hours of bilateral ureteral ligation in the rat.

Kidney function was studied in rats after the release of 24 hours of bilateral ureteral ligation (BUL). After deligation, natriuresis was observed for 1 day while diuresis persisted up to 4 days. The possible defective collecting tubule to reabsorb sodium may improve within 1 day, since the urinary sodium concentration was well below the sham value. During the early phase of deligation, the glomerular filtration rate (GFR) averaged only 15 per cent of the sham value. Heterogeneity of the surface nephrons was apparent. About 17 per cent of the observed surface nephrons had no tubular fluid flow, suggesting possibly that these nephrons may not contribute to the kidney GFR. In the other 83 per cent of the nephrons, the stop-flow pressure, 29.0 mm. Hg, was lower than the sham value, 33.6 mm. Hg, whereas the proximal tubular pressure of 15.1 mm. Hg was significantly above the sham value of 13.2 mm. Hg. Both these factors may have induced a reduction in the effective filtration pressure, from 20.1 to 13.9 mm. Hg, and may have contributed to the reduction in GFR in those functioning nephrons. Four days later, a similar proportion of the surface nephrons still showed a marked reduction in function, whereas others had improved significantly. The proximal tubular pressure, the stop-flow and the effective filtration pressures approached the sham values. These improvements may be associated with an increase in GFR to 42 per cent of the sham value. It is suggested that the prolong suppression of the kidney GFR may not be due to the drastic change in the glomerular capillary pressure of the surface nephrons, at this latter period.