Relation of the Saluresis of Urea and Mannitol Loading to the Normal Excretion of Electrolyte

Abstract

In hydrated dogs subjected to mild solute diuresis with mannitol and urea, the patterns of change in the course of the experiments in the ratios of sodium and chloride excretion to total solute excretion were not significantly different from those observed in control experiments conducted in an identical manner but in which no solute load was imposed. In hydrated, mildly acidotic dogs a similar result was obtained if only the mean values of the data are considered; in individual experiments loading produced considerable fluctuations in the ratios as compared with control experiments. Hydropenic animals, on the other hand, showed an increase in the sodium:total solute ratio with loading but the chloride:total solute ratio was not significantly affected. The potassium: total solute ratio was, in general, also independent of solute diuresis. In the hydropenic and hydrated acidotic animals the ratio was unaffected by loading but in the hydrated nonacidotic animals, considerable variability in excretion made interpretation of the ratios difficult. Ratios calculated in a similar manner for titratable acid, ammonia, bicarbonate and phosphorus all fell with loading. Reductions in filtration rate occasioned by urea loading had no effect on the ratios for sodium, potassium and chloride. The data appear to provide a link between the saluresis of solute loading and the normal excretion of electrolyte and suggest that the saluresis is simply a magnified operation of the normal mechanism concerned with electrolyte. The ratio of electrolyte to total solute would appear to be of physiological significance, differing from other parameters of electrolyte excretion in that it is independent of at least moderate fluctuations in the rate of nonelectrolyte excretion.