Influence of Prolonged Electrolyte Deprivation and Final Restoration on Fluid Intake, Balance and Distribution

Dogs partially depleted of extracellular electrolytes by intraperitoneal glucose injections and then maintained on a salt-free diet showed absence of fluid intake and a negative water balance while the intracellular volumes were above normal. When these volumes had been reduced to stable minimal levels, water was taken by mouth and the negative water balance corrected. Although the intakes now rose to polydipsic levels, a positive balance was not established despite the fact that the extracellular volumes were still reduced. Intracellular volumes were not restored to the preëxperi-mental level. When NaCl was given, extracellular electrolytes and volumes were restored toward normal. The initial response was an increased intake which, however, was not sustained. The intracellular compartment, originally decreased, showed a delayed rehydration to normal levels. Hence the voluntary water intake showed more positive correlation with changes in intracellular volume than with extracellular volume change. Fluid balance was affected both by intracellular hydration and electrolyte levels in the extracellular fluid.