title: Difference between hypertonic NaCl and NaHCO3 as osmotic diuretics in dog kidneys.
abstract: To compare the osmotic inhibitory effects of NaCl and NaHCO3 on proximal tubular fluid reabsorption, plasma osmolality was raised by 40 mosmol kg-1 H2O by infusing hypertonic NaCl and NaHCO3 in volume-expanded dogs receiving ethacrynic acid. In five dogs studied at constant plasma pH 7.5, both NaCl and NaHCO3 reduced water reabsorption by 29 +/- 2%. However, NaCl infusion reduced bicarbonate reabsorption by 31 +/- 2%, whereas bicarbonate reabsorption remained unchanged during NaHCO3 infusion. In six dogs, bicarbonate reabsorption was kept constant during NaCl and NaHCO3 infusion by adjustments of plasma pH. At similar glomerular filtration rates (42.4 +/- 2.9 ml min-1), water reabsorption was 28.7 +/- 1.7 ml min-1 in the control period, 29.4 +/- 2.5 ml min-1 during hypertonic NaCl infusion and 20.6 +/- 1.2 ml min-1 during hypertonic NaHCO3 infusion. Therefore, NaCl did not reduce proximal tubular water reabsorption by a direct osmotic effect. By calculating the regression coefficient for the relationship between measured chloride reabsorption and maximal convective chloride flux, the effective reflection coefficient for NaCl averaged 0.11 +/- 0.01. The combination of a low reflection coefficient and high permeability may explain why hypertonic NaCl is not an osmotic diuretic.
authors.affiliation: Institute for Experimental Medical Research, University of Oslo, Ullevaal Hospital, Norway.
authors.forename: J
authors.initials: J
authors.lastname: Ostensen
authors.forename: E S
authors.initials: ES
authors.lastname: Stokke
authors.forename: J F
authors.initials: JF
authors.lastname: Bugge
authors.forename: H
authors.initials: H
authors.lastname: Langberg
authors.forename: F
authors.initials: F
authors.lastname: Kiil
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism / Q000494:pharmacology*; D001834:Body Water / Q000378:metabolism; D004234:Diuretics, Osmotic / Q000494:pharmacology*; D004285:Dogs; D005919:Glomerular Filtration Rate / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D012462:Saline Solution, Hypertonic / Q000493:pharmacokinetics / Q000494:pharmacology*; D014882:Water-Electrolyte Balance / Q000187:drug effects
chemical_list: D001639:Bicarbonates; D004234:Diuretics, Osmotic; D012462:Saline Solution, Hypertonic