Increased water intake by rats maintained on high NaCl diet: analysis of ingestive behavior.

To determine the temporal relation between the ingestion of dry food containing 8% NaCl and the increased daily consumption of water that occurs when rats eat this diet, rats were placed in specially designed cages linked to microprocessors that allowed the continuous monitoring of food and water ingestion. The increase in water intake was found to result from increases both in number and size of individual drinking bouts. Approximately 75% of the water intake was consumed in drinking bouts that occurred less than 5 min after feeding. Indeed, rats rarely consumed 8% NaCl diet without also drinking water in the same ingestive episode, and the volume of water they drank was proportional to the food intake in that episode. These and other observations suggest that ingestion of the high salt diet stimulated thirst rapidly. As such, they are consistent with previous reports that visceral osmoreceptors (or Na(+)-receptors) detect osmolytes passing through the gastrointestinal tract and provide an early stimulus of thirst in rats that precedes large increases in systemic plasma osmolality.