Lack of evidence for gastrointestinal control of sodium excretion in unanesthetized dogs

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Abstract
Experiments were performed to determine whether the unanesthetized dog exhibits a greater natriuresis following an oral administration of a hypertonic NaCl solution (1.5 meq Na/kg) than following the i.v. administration of the same solution. Conditioned female dogs were placed on a low Na diet for 3 days, and on the 4th day a hypertonic NaCl solution (616 mM) was given either by stomach tube (GI) or i.v. while an equal volume of a hypotonic NaCl solution (31 mM) was given by the alternative route. The studies were repeated on each dog so that paired observations were obtained. Following the administration of the NaCl solutions no difference in urinary Na excretion was observed between the GI and i.v. administration of the hypertonic NaCl solution. Dogs that were fed immediately following either route of NaCl administration had a significant reduction in Na excretion, but no differences in Na excretion were found between the GI and i.v. routes of Na administration. In 6 dogs on a high Na diet (100 meq/day), the i.v. administration of a hypertonic solution produced a significantly greater natriuresis than that produced by the GI administration. No GI or portal Na+ receptor system that regulates urinary Na excretion was seen in the unanesthetized dog.