Secretion of salt and water into the medullary collecting duct of Ringer-infused rats

Authors:
  • HSH Sonnenberg
    H Sonnenberg
  • RMRobert Moss
    Robert Moss
  • ALAnita T. Layton
    Anita T. Layton
  • MRMadhumitha Rajagopal
    Madhumitha Rajagopal
  • STSheela V. Thomas
    Sheela V. Thomas
  • PKParu P. Kathpalia
    Paru P. Kathpalia
  • YCYu Chen
    Yu Chen
  • APAlan C. Pao
    Alan C. Pao
  • JWJonathan H. Widdicombe
    Jonathan H. Widdicombe
  • ARAbolfazl K. Rad
    Abolfazl K. Rad
  • RBRichard J. Balment
    Richard J. Balment
  • NANick Ashton
    Nick Ashton
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Abstract
Using a microcatheterization technique, the contribution of the collecting duct to the renal response to extracellular fluid volume expansion was studied in anesthetized rats. During intravenous infusion of Ringer solution (0.25 ml/min per 100 g body wt), urinary excretion of fluid, sodium, and potassium was 365 mul/min per g kidney wt (V), 52.6 mueq/min per g kidney wt (UNaV), and 3.86 mueq/min per g kidney wt (UKV), representing 23, 24, and 65% of filtered load, respectively. Analysis of collecting duct fluid from cortex and outer medulla indicated continued net reabsorption of ions and water in these nephron segments; in contrast, in inner medulla net secretion of Na, K, and fluid into the collecting duct was demonstrated. Addition of sodium and water was equivalent to approximately 10% of filtered load. It is concluded that under the stress of extreme intravenous fluid loading tubular secretion of salt and water into the inner medullary collecting duct contributes importantly to diuresis and natriuresis. The mechanism of such secretion remains undetermined.