Tubuloglomerular feedback responses during perfusion with nonelectrolyte solutions in the rat

Academic Article

Abstract

  • Previous studies in the dog have demonstrated that feedback-mediated decreases in stop-flow pressure (SFP) can occur during distal nephron perfusion with solutions containing either electrolytes or nonelectrolytes. In contrast, studies in the rat indicate that perfusion with nonelectrolyte solutions do not elicit decreases in SFP or single nephron GFR (SNGFR). The present study was conducted in the rat to evaluate SFP and SNGFR feedback responses to perfusion with an isotonic mannitol solution containing no electrolytes, and urea and mannitol solutions containing small quantities of electrolytes. The latter two solutions each contained 23 mEq of chloride per liter and are referred to as low-electrolyte solutions (LES). Results obtained with these solutions were compared with those obtained during perfusion with an artificial tubular fluid (ATF). In additional experiments, distal tubular fluid collections were taken during perfusion and measured for chloride concentration and osmolality. The maximal decrease in SNGFR from the control value was 58 ± 5% with ATF, 61 ± 8% with isotonic mannitol, 44 ± 5% with mannitol-LES, and 55 ± 6% with urea-LES. The maximum decrease in SFP from the control measurement was 11 ± 1 mm Hg with ATF, 10 ± 2 mm Hg with isotonic mannitol, 11.8 ± 1.0 mm Hg with mannitol-LES, and 12 ± 1 mm Hg with urea-LES. In the ATF series, increases in perfusion rate from 10 to 35 nl/min led to increases in chloride from 77 ± 6 to 120 ± 7 mEq/liter and in osmolality from 203 ± 8 to 259 ± 7 mOsm/kg. In the tubules perfused with mannitol-LES, chloride decreased from 81 ± 4 to 66 ± 4 mEq/liter; however, osmolality increased from 294 ± 9 to 322 ± 11 mOsm/kg. With urea-LES, chloride did not change significantly (66 ± 4 to 73 ± 6 mEq/liter) but, the osmolality rose from 200 ± 9 to 268 ± 11 mOsm/kg. These results demonstrate that tubuloglomerular feedback responses can be elicited during perfusion with solutions having low concentrations of electrolytes and with nonelectrolyte solutions. Furthermore, although distal perfusion with ATF led to concomitant increases in the chloride concentration and the osmolality, the distal chloride concentration did not increase significantly during perfusion with the solutions having low concentrations of electrolytes.
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    Author List

  • Bell PD; Navar LG; Ploth DW; McLean CB
  • Start Page

  • 460
  • End Page

  • 471
  • Volume

  • 18
  • Issue

  • 4